Transparent Interconnection of Lots of Links (TRILL): Adjacency
draft-ietf-trill-rfc6327bis-04
The information below is for an old version of the document that is already published as an RFC.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 7177.
|
|
|---|---|---|---|
| Authors | Donald E. Eastlake 3rd , Radia Perlman , Anoop Ghanwani , Howard Yang , Vishwas Manral | ||
| Last updated | 2015-10-14 (Latest revision 2014-01-10) | ||
| Replaces | draft-eastlake-trill-rfc6327bis | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | Proposed Standard | ||
| Formats | |||
| Reviews |
GENART Last Call review
(of
-02)
by Elwyn Davies
Almost ready
|
||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | Submitted to IESG for Publication | |
| Document shepherd | Jon Hudson | ||
| Shepherd write-up | Show Last changed 2013-10-25 | ||
| IESG | IESG state | Became RFC 7177 (Proposed Standard) | |
| Action Holders |
(None)
|
||
| Consensus boilerplate | Yes | ||
| Telechat date | (None) | ||
| Responsible AD | Ted Lemon | ||
| Send notices to | (None) | ||
| IANA | IANA review state | Version Changed - Review Needed | |
| IANA action state | No IANA Actions |
draft-ietf-trill-rfc6327bis-04
TRILL Working Group Donald Eastlake
INTERNET-DRAFT Huawei
Obsoletes: 6327 Radia Perlman
Updates: 6325 Intel Labs
Intended status: Proposed Standard Anoop Ghanwani
Dell
Howard Yang
Cisco
Vishwas Manral
HP
Expires: July 9, 2014 January 10, 2014
TRILL: Adjacency
<draft-ietf-trill-rfc6327bis-04.txt>
Abstract
The IETF TRILL (TRansparent Interconnection of Lots of Links)
protocol supports arbitrary link technologies between TRILL switches
including point-to-point links and multi-access LAN (Local Area
Network) links that can have multiple TRILL switches and end stations
attached. TRILL uses IS-IS (Intermediate System to Intermediate
System) routing. This document specifies the establishment,
reporting, and termination of IS-IS adjacencies between TRILL
switches, also known as RBridges. It also concerns four other link-
local aspects of TRILL: Designated RBridge (DRB) selection, MTU
(Maximum Transmission Unit) testing, pseudonode creation, and BFD
(Bi-Directional Forwarding Detection) session bootstrapping in
connection with adjacency. State diagrams are included where
appropriate. This document obsoletes RFC 6327 and updates RFC 6325.
Status of This Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Distribution of this document is unlimited. Comments should be sent
to the TRILL working group mailing list.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
D. Eastlake, et al [Page 1]
INTERNET-DRAFT TRILL: Adjacency
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/1id-abstracts.html. The list of Internet-Draft
Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
D. Eastlake, et al [Page 2]
INTERNET-DRAFT TRILL: Adjacency
Table of Contents
1. Introduction............................................4
1.1 Content and Precedence.................................5
1.2 Terminology and Acronyms...............................5
2. The TRILL Hello Environment and Purposes................6
2.1 RBridge Interconnection by Ethernet....................6
2.2 Handling Native Frames.................................7
2.3 Zero or Minimal Configuration..........................8
2.4 MTU Robustness.........................................8
2.5 Purposes of the TRILL Hello Protocol...................8
3. Adjacency State Machinery..............................10
3.1 TRILL Hellos, Ports, and VLANs........................10
3.2 Adjacency Table Entries and States....................11
3.3 Adjacency and Hello Events............................12
3.4 Adjacency State Diagram and Table.....................15
3.5 Multiple Parallel Links...............................16
3.6 Insufficient Space in Adjacency Table.................17
4. LAN Ports and DRB State................................18
4.1 Port Table Entries and DRB Election State.............18
4.2 DRB Election Events...................................19
4.2.1 DRB Election Details................................20
4.2.2 Change in DRB.......................................20
4.2.3 Change in Designated VLAN...........................21
4.3 State Table and Diagram...............................21
5. MTU Matching...........................................23
6. BFD Enabled and BFD Session Bootstrap..................25
7. Pseudonodes............................................27
8. More TRILL Hello Details...............................28
8.1 Contents of TRILL Hellos..............................28
8.2 Transmitting TRILL Hellos.............................29
8.2.1 TRILL Neighbor TLVs.................................29
8.3 Receiving TRILL Hellos................................30
9. Multiple Ports on the Same Broadcast Link..............32
10. Security Considerations...............................33
11. IANA Considerations...................................33
Appendix A: Changes from [RFC6327]........................34
Appendix B: Changes to [RFC6325]..........................35
Appendix Z: Change History................................36
Normative References......................................37
Informative References....................................37
Acknowledgements..........................................39
Authors' Addresses........................................40
D. Eastlake, et al [Page 3]
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1. Introduction
The IETF TRILL (TRansparent Interconnection of Lots of Links)
protocol [RFC6325] provides optimal pair-wise data frame forwarding
without configuration, safe forwarding even during transient loops,
and support for transmission of both unicast and multicast traffic
taking advantage of multiple paths in multi-hop networks with
arbitrary topology. End stations are connected to TRILL switches
with Ethernet but TRILL switches can be interconnected with arbitrary
link technology. TRILL accomplishes this by using [IS-IS]
(Intermediate System to Intermediate System) link state routing
[RFC1195] [RFC6326bis] and a header in TRILL data packets that
includes a hop count. The design supports data labeling by VLANs
(Virtual Local Area Networks) and fine grained labels [RFCfgl] as
well as optimization of the distribution of multi-destination frames
based on data label and multicast groups. Devices that implement
TRILL are called TRILL switches or RBridges (Routing Bridges).
This document provides detailed specification for five of the link-
local aspects of the TRILL protocol used on broadcast links (also
called LAN or multi-access links), and for the three of these aspects
used on point-to-point links. It includes state diagrams and
implementation details where appropriate. Alternative
implementations that interoperate on the wire are permitted.
The scope of this document is limited to the following aspects of the
TRILL protocol with applicability and the most relevant section of
this document as shown:
LAN P2P Section Link-Local Aspect
--- --- ------- -----------------
X X 3 Adjacency formation and dissolution
X 4 DRB (Designated RBridge) election
X X 5 MTU (Maximum Transmission Unit) matching
X X 6 1-hop BFD (Bi-directional Forwarding Detection)
for adjacency
X 7 Creation and use of pseudonodes [IS-IS]
Table 1. LAN/P2P Applicability
There is no DRB (also known as DIS (Designated Intermediate System))
election and no pseudonode creation on links configured as point-to-
point.
For other aspects of the TRILL protocol, see other documents such as
[RFC6325], [RFC6439], [RFCclear], and [ESADI].
This document obsoletes [RFC6327]. See Appendix A for a summary of
changes from [RFC6327]. This document updates [RFC6325] as described
D. Eastlake, et al [Page 4]
INTERNET-DRAFT TRILL: Adjacency
in Appendix B.
1.1 Content and Precedence
In case of conflict between this document and [RFC6325], this
document prevails.
Section 2 below explains the rationale for the differences between
the TRILL Hello protocol and the Layer 3 IS-IS Hello protocol in
light of the environment for which the TRILL protocol is designed.
It also describes the purposes of the TRILL Hello protocol.
Section 3 describes the adjacency state machine, its states, and its
relevant events.
Section 4 describes the Designated RBridge (DRB) election state
machine for RBridge LAN ports, its states, and its relevant events.
Section 5 describes MTU testing and matching on a TRILL link.
Section 6 discusses one-hop BFD session bootstrapping in connection
with adjacency.
Section 7 discusses pseudonode creation and use on LAN links.
Section 8 provides more details on the reception and transmission of
TRILL Hellos.
Section 9 discusses the case of multiple ports from one RBridge on
the same link.
1.2 Terminology and Acronyms
This document uses the acronyms defined in [RFC6325] supplemented by
the following additional acronyms:
BFD - Bi-directional Forwarding Detection [RFCbfd].
SNPA - Subnetwork Point of Attachment [IS-IS].
TRILL switch - an alternative name for an RBridge.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
D. Eastlake, et al [Page 5]
INTERNET-DRAFT TRILL: Adjacency
2. The TRILL Hello Environment and Purposes
[IS-IS] has subnetwork-independent functions and subnetwork-dependent
functions. Currently, Layer 3 use of IS-IS supports two types of
subnetworks: (1) point-to-point link subnetworks between routers and
(2) general broadcast (LAN) subnetworks. Because of the differences
between the environment of Layer 3 routers and the environment of
TRILL RBridges, instead of the subnetwork-dependent functions used at
Layer 3, which are specified in [IS-IS] Sections 8.2 and 8.4, the
TRILL protocol uses modified subnetwork-dependent functions for
point-to-point subnetworks and broadcast (LAN) subnetworks. The
differences between the TRILL and Layer 3 environments are described
in Sections 2.1 through 2.4 followed by a summation, in Section 2.5,
of the purposes of the TRILL Hello protocol.
2.1 RBridge Interconnection by Ethernet
TRILL supports the interconnection of RBridges by multi-access LAN
links such as Ethernet. Because this includes general bridged LANs
[802.1Q], the links between RBridges may contain devices or services
that can restrict VLAN connectivity, such as [802.1Q] bridges or
carrier Ethernet services. In addition, RBridge Ethernet ports, like
[802.1Q] ports, can be configured to restrict input/output on a VLAN
basis.
For this reason TRILL Data and TRILL IS-IS packets are sent on
Ethernet links in a Designated VLAN that is assumed to provide
connectivity between all RBridges on the link. The Designated VLAN
is dictated for a LAN link by the elected Designated RBridge on that
link (DRB, equivalent to the Designated Intermediate System at Layer
3). On an RBridge Ethernet port configured as point-to-point, TRILL
Data and IS-IS packets are sent in that port's Desired Designated
VLAN regardless of the state of any other ports on the link.
Connectivity on an Ethernet link configured as point-to-point
generally depends on both ends being configured with the same Desired
Designated VLAN. Because TRILL Data packets flow between RBridges on
an Ethernet link only in the link's Designated VLAN, adjacency for
routing calculations is based only on connectivity characteristics in
that VLAN.
(Non-Ethernet links, such as PPP [RFC6361] generally do not have any
Outer.VLAN labeling so the Designated VLAN for such links has no
effect.)
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2.2 Handling Native Frames
This section discusses the handling of "native" frames as defined in
Section 1.4 of [RFC6325]. As such, this section is not applicable to
point-to-point links between TRILL switches or any link where all the
TRILL switch ports on the link have been configured as "trunk ports"
by setting the end-station service disable bit for the port (see
Section 4.9.1 of [RFC6325]).
Layer 3 data packets, such as IP packets, are already "tamed" when
they are originated by an end station: they include a hop count and
Layer 3 source and destination address fields. Furthermore, for
ordinary data packets, there is no requirement to preserve any outer
Layer 2 addressing and, if the packets are unicast, they are
explicitly addressed to their first hop router.
In contrast, TRILL switches must accept, transport, and deliver
"untamed" native frames: Native frames that lack a hop count field
usable by TRILL and have Layer 2 MAC addresses that indicate their
source and destination. These Layer 2 addresses must be preserved
for delivery to the native frame's Layer 2 destination. One
resulting difference is that RBridge ports providing native frame
service must receive in promiscuous MAC (Media Access Control)
address mode, while Layer 3 router ports typically receive in a
selective MAC address mode.
TRILL handles these requirements by having, on the link where an end
station originates a native frame, one RBridge "ingress" such a
locally originated native frame by adding a TRILL Header that
includes a hop count, thus converting it to a TRILL Data packet.
This augmented packet is then routed to one RBridge on the link
having the destination end station for the frame (or one RBridge on
each such link if it is a multi-destination frame). Such final
RBridges perform an "egress" function, removing the TRILL Header and
delivering the original frame to its destination(s). (For the
purposes of TRILL, a Layer 3 router is an end station.)
Care must be taken to avoid a loop that would involve egressing a
native frame and then re-ingressing it because, while it is in native
form, it would not be protected by a hop count and could loop
forever. Such a loop could even, for multi-destination frames,
involve multiplication of the number of frames each time around and
would likely saturate all links involved within milliseconds. For
TRILL, safety against such loops for a link is more important than
transient loss of data connectivity on that link.
The primary TRILL defense mechanism against such loops, which is
mandatory, is to assure that, as far as practically possible, there
is only a single RBridge that is in charge of ingressing and
egressing native frames from and to a link where TRILL is offering
D. Eastlake, et al [Page 7]
INTERNET-DRAFT TRILL: Adjacency
end station service. This is the Designated RBridge and appointed
forwarder mechanism initially specified in the TRILL base protocol
[RFC6325], discussed in Section 2.5 below, and further specified both
in Section 4 below and [RFC6439].
2.3 Zero or Minimal Configuration
TRILL provides connectivity and least cost paths with zero
configuration. For additional services, it strives to require only
minimal configuration; however, services that require configuration
when offered by [802.1Q] bridges, such as non-default VLAN or
priority, will require configuration. This differs from Layer 3
routing where routers typically need to be configured as to the
subnetworks connected to each port, etc., to provide service.
2.4 MTU Robustness
TRILL IS-IS needs to be robust against links with reasonably
restricted MTUs, including links that accommodate only the classic
Ethernet frame size, despite the addition of reasonable headers such
as VLAN tags. Such robustness is particularly required for TRILL
Hellos to assure correct adjacency and the election of a unique DRB
on LAN links.
TRILL will also be used inside data centers where it is common for
all or most of the links and switches to support frames substantially
larger than the classic Ethernet maximum size. For example, they may
have an MTU adequate to comfortably handle Fiber Channel over
Ethernet frames, for which T11 recommends a 2,500-byte MTU [FCoE], or
even 9K byte jumbo frames. It would be beneficial for a TRILL campus
with such a large MTU to be able to safely make use of it.
These needs are met by a mandatory maximum on the size of TRILL
Hellos and by the optional use of MTU testing as described below.
2.5 Purposes of the TRILL Hello Protocol
There are three purposes for the TRILL Hello protocol. They are
listed below along with a reference to the section of this document
in which each is discussed:
a) To determine which RBridge neighbors have acceptable connectivity
to be reported as part of the topology (Section 3)
D. Eastlake, et al [Page 8]
INTERNET-DRAFT TRILL: Adjacency
b) To elect a unique Designated RBridge on broadcast (LAN) links
(Section 4)
c) To determine the MTU with which it is possible to safely
communicate with each RBridge neighbor (Section 5)
In Layer 3 IS-IS, all three of these functions are combined. Hellos
may be padded to the maximum length (see [RFC3719], Section 6) so
that a router neighbor is not even discovered if it is impossible to
communicate with it using maximum-sized Layer 3 IS-IS packets. Also,
even if Hellos from a neighbor R2 are received by R1, if connectivity
to R2 is not 2-way (i.e., R2 does not list R1 in R2's Hello), then R1
does not consider R2 as a Designated Intermediate System (Designated
Router) candidate. Because of this logic, it is possible at Layer 3
for multiple Designated Routers to be elected on a LAN, with each
representing the LAN as a pseudonode. It appears to the topology as
if the LAN is now two or more separate LANs. Although this is
surprising, this does not cause problems for Layer 3.
In contrast, this behavior is not acceptable for TRILL, since in
TRILL it is important that all RBridges on a link know about each
other, and on broadcast (LAN) links that they choose a single RBridge
to be the DRB to control the native frame ingress and egress.
Otherwise, multiple RBridges might ingress/egress the same native
frame, forming loops that are not protected by the hop count in the
TRILL header as discussed above.
The TRILL Hello protocol is best understood by focusing separately on
each of these three functions listed above which we do in Sections 3,
4, and 5.
One other issue with TRILL LAN Hellos is to ensure that subsets of
the information can appear in any single message, and be processable,
in the spirit of IS-IS Link State PDUs (LSPs) and Complete Sequence
Number PDUs (CSNPs). LAN TRILL Hello packets, even though they are
not padded, can become very large. An example where this might be
the case is when some sort of backbone technology interconnects
hundreds of TRILL sites over what would appear to TRILL to be a giant
Ethernet, where the RBridges connected to that cloud will perceive
that backbone to be a single link with hundreds of neighbors. Thus,
the TRILL LAN Hello uses a different Neighbor TLV [RFC6326bis] that
lists neighbors seen for a range of MAC (SNPA) addresses.
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3. Adjacency State Machinery
Each RBridge port has associated with it a port state, as discussed
in Section 4, and a table of zero or more adjacencies (if the port is
configured as point-to-point, zero or one) as discussed in this
section. The states such adjacencies can have, the events that cause
adjacency state changes, the actions associated with those state
changes, a state table, and a state diagram are given below.
3.1 TRILL Hellos, Ports, and VLANs
The determination of adjacencies on links is made using TRILL Hellos
(see Section 8), an optional MTU test (see Section 5), and optionally
BFD (see Section 6) and/or other connectivity tests. If the MAC
(SNPA) address of more than one RBridge port on a broadcast link are
the same, all but one of such ports are put in the Suspended state
(see Section 4) and do not participate in the link except to monitor
whether they should stay suspended. If the two ports on a point-to-
point link have MAC (SNPA) addresses it does not affect TRILL
operation if they are the same. (PPP ports, for example, do not have
MAC addresses [RFC6361].)
The following items MUST be the same for all TRILL Hellos issued by
an RBridge on a particular Ethernet port regardless of the VLAN in
which the Hello is sent:
- Source MAC address,
- Priority to be DRB,
- Desired Designated VLAN,
- Port ID, and,
- if included, BFD Enabled TLV [RFC6213] and PORT-TRILL-VER sub-
TLV [RFC6326bis].
Of course, the priority, Desired Designated VLAN, and possibly the
inclusion or value of the PORT-TRILL-VER sub-TLV, and/or BFD Enabled
TLV can change on occasion, but then the new value(s) must similarly
be used in all TRILL Hellos on the LAN port, regardless of VLAN.
On broadcast links:
Because bridges acting as glue on an Ethernet broadcast link might
be configured in such a way that some VLANs are partitioned, it is
necessary for RBridges to transmit Hellos on Ethernet links with
multiple VLAN tags. The conceptually simplest solution may have
been to have RBridges transmit up to 4,094 times as many Hellos,
one with each legal VLAN ID enabled at each port, but this would
obviously have deleterious performance implications. So, the
TRILL protocol specifies that if RB1 knows it is not the DRB, it
D. Eastlake, et al [Page 10]
INTERNET-DRAFT TRILL: Adjacency
transmits its Hellos on only a limited set of VLANs. Only an
RBridge that believes itself to be the DRB on a broadcast Ethernet
link "sprays" its TRILL Hellos on all of its enabled VLANs at the
port. And in both cases, an RBridge can be configured to send
Hellos on only a subset of those VLANs. The details are given in
[RFC6325], Section 4.4.3.
On point-to-point links:
If the link technology is VLAN sensitive, such as Ethernet, an
RBridge sends TRILL Hellos only in the Desired Designated VLAN for
which it is configured.
3.2 Adjacency Table Entries and States
Each adjacency on broadcast links and the one possible adjacency on
each point-to-point link is in one of four states. An RBridge
participates in LSP synchronization at a port as long as it has one
or more adjacencies out that port that are in the 2-way or Report
state.
Down:
This is a virtual state for convenience in creating state
diagrams and tables. It indicates that the adjacency is non-
existent, and there is no entry in the adjacency table for it.
Detect:
A neighbor RBridge has been detected through receipt of a TRILL
Hello but either 2-way connectivity has not been confirmed or
the detection was on an Ethernet link in a VLAN other than the
Designated VLAN.
2-Way:
2-way connectivity to the neighbor has been found and, if the
link is Ethernet, it was found on the Designated VLAN, but some
enabled test, such as MTU meeting the minimum campus
requirement or BFD confirming connectivity, has not yet
succeeded.
Report:
There is 2-way connectivity to the neighbor (on the Designated
VLAN if an Ethernet link) and all enabled tests have succeeded
including, if enabled, MTU and/or BFD testing. This state will
cause adjacency to be reported in an LSP (with appropriate
provision for a pseudonode, if any, as described in Section 7).
For an adjacency in any of the three non-Down states (Detect, 2-Way,
or Report), there will be an adjacency table entry. That entry will
D. Eastlake, et al [Page 11]
INTERNET-DRAFT TRILL: Adjacency
give the state of the adjacency and will also include the information
listed below.
o The address, if any, of the neighbor, the Port ID, and the
System ID in the received Hellos. Together, these three
quantities uniquely identify the adjacency on a broadcast link.
o For a point-to-point adjacency, there is a single Hello holding
timer. For a broadcast LAN adjacency, there are exactly two
Hello holding timers: a Designated VLAN holding timer and a
non-Designated VLAN holding timer. Each timer consists of a
16-bit unsigned integer number of seconds.
o If the adjacency is on a broadcast link, the 7-bit unsigned
priority of the neighbor to be the DRB.
o The 5 bytes of data from the PORT-TRILL-VER received in the
most recent TRILL Hello from the neighbor RBridge.
o The VLAN that the neighbor RBridge wants to be the Designated
VLAN on the link, called the Desired Designated VLAN.
o For an adjacency table at an RBridge that supports BFD, a flag
indicating whether the last received TRILL Hello from the
neighbor RBridge contained a BFD Enabled TLV (see Section 6).
3.3 Adjacency and Hello Events
The following events can change the state of an adjacency:
A0. Receive a TRILL Hello for a broadcast LAN adjacency whose
source MAC address (SNPA) is equal to that of the port on
which it is received. This is a special event that cannot
occur on a port configured as point-to-point and is handled as
described immediately after this list of events. It does not
appear in the state transition table or diagram.
A1. Receive a TRILL Hello (other than an A0 event) such that:
- If received on an Ethernet port, it was received in the
Designated VLAN.
- If received for a broadcast LAN adjacency, it contains a
TRILL Neighbor TLV that explicitly lists the receiving
port's (SNPA) address.
- If received for a point-to-point adjacency, it contains a
Three-Way Handshake TLV with the receiver's System ID and
Extended Circuit ID.
A2. Event A2 is not possible for a port configured as point-to-
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point. Receive a TRILL Hello (other than an A0 event) such
that either
- The port is Ethernet and the Hello was not on the
Designated VLAN (any TRILL Neighbor TLV in such a Hello is
ignored), or
- The Hello does not contain a TRILL Neighbor TLV covering an
address range that includes the receiver's (SNPA) address.
A3. Receive a TRILL Hello (other than an A0 event) such that:
- If received on an Ethernet port, it was received in the
Designated VLAN.
- If received for a broadcast LAN adjacency, it contains one
or more TRILL Neighbor TLVs covering an address range that
includes the receiver's (SNPA) address and none of which
lists the receiver.
- If received for a point-to-point adjacency, it contains a
Three-Way Handshake TLV with either the System ID or
Extended Circuit ID or both not equal to that of the
receiver.
A4. Either (1) the Hello holding timer expires on a point-to-point
adjacency or (2), on a broadcast LAN adjacency, (2a) both
Hello timers expire simultaneously or (2b) one Hello timer
expires when the other Hello timer is already in the expired
state.
A5. For a broadcast LAN adjacency, the Designated VLAN Hello
holding timer expires, but the non-Designated VLAN Hello
holding timer still has time left until it expires. This event
cannot occur for a point-to-point adjacency.
A6. MTU if enabled, BFD if enabled, and all other enabled
connectivity tests successful.
A7. MTU if enabled, BFD if enabled, and all other enabled
connectivity tests were successful but one or more now fail.
A8. The RBridge port goes operationally down.
For the special A0 event, the Hello is examined to determine if it
has a higher priority than the port on which it is received such that
the sending port should be the DRB as described in Section 4.2.1. If
the Hello is of lower priority than the receiving port, it is
discarded with no further action. If it is of higher priority than
the receiving port, then any adjacencies for the receiving port are
discarded (transitioned to the Down state), and the port is suspended
as described in Section 4.2.
The receipt of a TRILL Hello that is not an event A0, causes the
following actions (except where the Hello would have created a new
D. Eastlake, et al [Page 13]
INTERNET-DRAFT TRILL: Adjacency
adjacency table entry but both the adjacency table is full and the
Hello is too low priority to displace an existing entry as described
in Section 3.6). The Designated VLAN referred to is the Designated
VLAN dictated by the DRB determined without taking the received TRILL
LAN Hello into account (see Section 4) for a broadcast LAN and the
local Desired Designated VLAN for a port configured as point-to-
point.
o If the receipt of a Hello creates a new adjacency table entry,
the neighbor RBridge MAC (SNPA) address (if any), Port ID, and
System ID are set from the Hello.
o For a point-to-point adjacency, the Hello holding timer is set
from the Holding Time field of the Hello. For a broadcast link
adjacency, the appropriate Hello holding timer for that
adjacency, depending on whether or not the Hello was received
in the Designated VLAN, is set to the Holding Time field of the
Hello and if the receipt of the LAN Hello is creating a new
adjacency table entry, the other timer is set to expired.
o For a broadcast link adjacency, the priority of the neighbor
RBridge to be the DRB is set to the priority field of the LAN
Hello.
o For a broadcast link adjacency, the VLAN that the neighbor
RBridge wants to be the Designated VLAN on the link is set from
the Hello.
o The five bytes of PORT-TRILL-VER data are set from that sub-TLV
in the Hello or set to zero if that sub-TLV does not occur in
the Hello.
o For a broadcast link, if the creation of a new adjacency table
entry or the priority update above changes the results of the
DRB election on the link, the appropriate RBridge port event
(D2 or D3) occurs, after the above actions, as described in
Section 4.2.
o For a broadcast link adjacency, if there is no change in the
DRB, but the neighbor Hello is from the DRB and has a changed
Designated VLAN from the previous Hello received from the DRB,
the result is a change in Designated VLAN for the link as
specified in Section 4.2.3.
An event A4 resulting in the adjacency transitioning to the Down
state may also result in an event D3 as described in Section 4.2.
Concerning events A6 and A7, if none of MTU, BFD, or other testing is
enabled, A6 is considered to occur immediately upon the adjacency
entering the 2-Way state, and A7 cannot occur.
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See further TRILL Hello receipt details in Section 7.
3.4 Adjacency State Diagram and Table
The table below shows the transitions between the states defined
above based on the events defined above:
| Event | Down | Detect | 2-Way | Report |
+-------+--------+--------+--------+--------+
| A1 | 2-Way | 2-Way | 2-Way | Report |
| A2 | Detect | Detect | 2-Way | Report |
| A3 | Detect | Detect | Detect | Detect |
| A4 | N/A | Down | Down | Down |
| A5 | N/A | Detect | Detect | Detect |
| A6 | N/A | N/A | Report | Report |
| A7 | N/A | N/A | 2-Way | 2-Way |
| A8 | Down | Down | Down | Down |
Table 2. Adjacency State Table
N/A indicates that the event to the left is Not Applicable in the
state at the top of the column. These events affect only a single
adjacency. The special A0 event transitions all adjacencies to Down,
as explained immediately after the list of adjacency events above.
The diagram below presents the same information as that in the state
table:
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+---------------+
| Down |<--------+
+---------------+ |
| | ^ | |
A2,A3| |A8| |A1 |
| +--+ | |
| +-----------|---+
V | |
+----------------+ A4,A8 | |
+----->| Detect |------->| |
| +----------------+ | |
| | | ^ | |
| A1| |A2,A3,A5 | | |
| | +---------+ | |
| | | |
| | +------------|---+
| | | |
| V V |
|A3,A5 +----------------+ A4,A8 |
|<-----| 2-Way |------->|
| +----------------+ |
| | ^ | ^ |
| A6| | |A1,A2,A7| |
| | | +--------+ |
| | | |
| | |A7 |
| V | |
|A3,A5 +-------------+ A4,A8 |
|<-----| Report |---------->|
+-------------+
| ^
|A1,A2,A6 |
+---------+
Figure 1. Adjacency State Diagram
3.5 Multiple Parallel Links
There can be multiple parallel adjacencies between neighbor RBridges
that are visible to TRILL. (Multiple low-level links that have been
bonded together by technologies such as link aggregation [802.1AX]
appear to TRILL as a single link over which only a single TRILL
adjacency can be established.)
Any such links that have pseudonodes (see Section 7) are
distinguished in the topology; such adjacencies, if they are in the
Report state, appear in LSPs as per Section 7. However, there can be
multiple parallel adjacencies without pseudonodes because they are
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INTERNET-DRAFT TRILL: Adjacency
point-to-point adjacencies or LAN adjacencies for which a pseudonode
is not being created. Such parallel, non-pseudonode adjacencies in
the Report state appear in LSPs as a single adjacency. The cost of
such an adjacency MAY be adjusted downwards to account for the
parallel paths. Multipathing across such parallel connections can be
freely done for unicast TRILL Data traffic on a per-flow basis but is
restricted for multi-destination traffic, as described in Section
4.5.2 (point 3) and Appendix C of [RFC6325].
3.6 Insufficient Space in Adjacency Table
If the receipt of a TRILL Hello would create a new adjacency table
entry (that is, would transition an adjacency out of the Down state),
there may be no space for the new entry. It is RECOMMENDED, for
ports configured as point-to-point and which can thus only have zero
or one adjacency not in the Down state, to reserved space for one
adjacency so that this condition cannot occur.
When there is adjacency table space exhaustion, the DRB election
priority (see Section 4.2.1) of the new entry that would be created
is compared with that priority for the existing entries. If the new
entry is higher priority than the lowest priority existing entry, it
replaces the lowest priority existing entry, which is transitioned to
the Down state.
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4. LAN Ports and DRB State
This section specifies the DRB election process in TRILL at a
broadcast (LAN) link port. Since there is no such election when a
port is configured as point-to-point, this section does not apply in
that case.
The information at an RBridge associated with each of its broadcast
LAN ports includes the following:
o Enablement bit, which defaults to enabled.
o The five bytes of PORT-TRILL-VER sub-TLV data used in TRILL
Hellos sent on the port.
o SNPA address (commonly a 48-bit MAC address) of the port.
o Port ID, used in TRILL Hellos sent on the port.
o The Holding Time, used in TRILL Hellos sent on the port.
o The Priority to be the DRB, used in TRILL LAN Hellos sent on
the port.
o If the port supports BFD, a BFD enabled flag that controls
whether or not a BFD Enabled TLV is included in TRILL Hellos
sent on the port.
o The DRB state of the port, determined as specified below.
o A 16-bit unsigned Suspension timer, measured in seconds.
o The desired Designated VLAN. The VLAN this RBridge wants to be
the Designated VLAN for the link out this port, used in TRILL
Hellos sent on the port if the link is Ethernet.
o A table of zero or more adjacencies (see Section 3).
4.1 Port Table Entries and DRB Election State
The TRILL equivalent of the DIS (Designated Intermediate System) on a
broadcast link is the DRB or Designated RBridge. The DRB election
state machinery is described below.
Each RBridge port that is not configured as point-to-point is in one
of the following four DRB states:
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Down:
The port is operationally down. It might be administratively
disabled or down at the link layer. In this state, there will
be no adjacencies for the port, and no TRILL Hellos or other
TRILL IS-IS PDUs or TRILL Data packets are accepted or
transmitted.
Suspended:
Operation of the port is suspended because there is a higher
priority port on the link with the same MAC (SNPA) address.
This is the same as the down state with the exception that
TRILL Hellos are accepted for the sole purpose of determining
whether to change the value of the Suspension timer for the
port as described below.
DRB:
The port is the DRB and can receive and transmit TRILL Data
packets.
Not DRB:
The port is deferring to another port on the link, which it
believes is the DRB, but can still receive and transmit TRILL
Data packets.
4.2 DRB Election Events
The following events can change the DRB state of a port. Note that
this is only applicable to broadcast links. There is no DRB state or
election at a port configured to be point-to-point.
D1. Expiration of the suspension timer while the port is in the
Suspended state or the enablement of the port.
D2. The adjacency table for the port changes and there are now
entries for one or more other RBridge ports on the link that
appear to be higher priority to be the DRB than the local
port.
D3. The port is not Down or Suspended, and the adjacency table for
the port changes, so there are now no entries for other
RBridge ports on the link that appear to be higher priority to
be the DRB than the local port.
D4. Receipt of a TRILL LAN Hello with the same MAC address (SNPA)
as the receiving port and higher priority to be the DRB as
described for event A0.
D5. The port becomes operationally down.
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Event D1 is considered to occur on RBridge boot if the port is
administratively and link-layer enabled.
Event D4 causes the port to enter the Suspended state and all
adjacencies for the port to be discarded (transitioned to the Down
state). If the port was in some state other than Suspended, the
suspension timer is set to the Holding Time in the Hello that causes
event D4. If it was in the Suspended state, the suspension timer is
set to the maximum of its current value and the Holding Time in the
Hello that causes event D4.
4.2.1 DRB Election Details
Events D2 and D3 constitute losing and winning the DRB election at
the port, respectively.
The candidates for election are the local RBridge and all RBridges
with which there is an adjacency on the port in an adjacency state
other than Down state. The winner is the RBridge with highest
priority to be the DRB, as determined from the 7-bit priority field
in that RBridge's Hellos received and the local port's priority to be
the DRB field, with MAC (SNPA) address as a tiebreaker, Port ID as a
secondary tiebreaker, and System ID as a tertiary tiebreaker. These
fields are compared as unsigned integers with the larger magnitude
being considered higher priority.
Resort to the secondary and tertiary tiebreakers should only be
necessary in rare circumstances when multiple ports have the same
priority and MAC (SNPA) address and some of them are not yet
suspended. For example, RB1, that has low priority to be the DRB on
the link, could receive Hellos from two other ports on the link that
have the same MAC address as each other and are higher priority to be
the DRB. One of these two ports with the same MAC address will be
suspended, cease sending Hellos, and the Hello from it received by
RB1 will eventually time out. But, in the meantime, RB1 can use the
tiebreakers to determine which port is the DRB and thus which port's
Hello to believe for such purposes as setting the Designated VLAN on
the link.
4.2.2 Change in DRB
Events D2 and D3 result from a change in the apparent DRB on the
link. Unnecessary DRB changes should be avoided, especially on links
offering native frame service, as a DRB change will generally cause a
transient interruption to native frame service.
D. Eastlake, et al [Page 20]
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If a change in the DRB on the link changes the Designated VLAN on an
Ethernet link, the actions specified in Section 4.2.3 are taken.
If an RBridge changes in either direction between being the DRB and
not being the DRB at a port, this will generally change the VLANs on
which that RBridge sends Hellos through that port, as specified in
Section 4.4.3 of [RFC6325].
4.2.3 Change in Designated VLAN
Unnecessary changes in the Designated VLAN on an Ethernet link should
be avoided because a change in the Designated VLAN can cause a
transient interruption to adjacency and thus to TRILL Data forwarding
on the link. When practical, all RBridge ports on a link should be
configured with the same Desired Designated VLAN so that, in case the
winner of the DRB election changes, for any reason, the Designated
VLAN will remain the same.
If an RBridge detects a change in Designated VLAN on an Ethernet
link, then, for all adjacency table entries for a port to that link,
the RBridge takes the following steps in the order given.
o The non-Designated VLAN Hello Holding timer is set to the
maximum of its time to expiration and the current time to
expiration of the Designated VLAN Hello Holding timer.
o The Designated VLAN Hello Holding timer is then set to expired
(if necessary), and an event A5 occurs for the adjacency (see
Section 3.3).
If the Designated VLAN for a link changes, this will generally change
the VLANs on which Hellos are sent by an RBridge port on that link as
specified in Section 4.4.3 of [RFC6325].
4.3 State Table and Diagram
The table below shows the transitions between the DRB states defined
above based on the events defined above:
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| Event | Down | Suspend | DRB | Not DRB |
+-------+--------+---------+---------+---------+
| D1 | DRB | DRB | N/A | N/A |
| D2 | N/A | N/A | Not DRB | Not DRB |
| D3 | N/A | N/A | DRB | DRB |
| D4 | N/A | Suspend | Suspend | Suspend |
| D5 | Down | Down | Down | Down |
Table 3. Port State Table
N/A indicates that the event to the left is Not Applicable in the
state at the top of the column.
The diagram below presents the same information as in the state
table:
+-------------+
| Down |<--------------+
+-+---+-------+ ^ |
| | ^ | |
D1| |D5 | | |
| +---+ |D5 |
| | |
| +--------+----+ |
| | Suspended |<---|---+
| +-+-----+-----+ | |
| D1| ^ | ^ | |
| | | |D4 | | |
| | | +---+ | |
| | | | |
| | |D4 | |
V V | | |
+---------------+-+ D5 | |
| DRB |---------->| |
+--------+--+-----+ | |
^ | | ^ | |
| D2| |D3| | |
| | +--+ | |
| | D4 | |
|D3 | +-----------------|---+
| V | |
+----+-------+-+ D5 |
| Not DRB |-------------->|
+----+---------+
| ^
|D2 |
+----+
Figure 2. Port State Diagram
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INTERNET-DRAFT TRILL: Adjacency
5. MTU Matching
The purpose of MTU testing is to ensure that the links used in the
campus topology can pass TRILL IS-IS packets, particularly LSP PDUs,
at the TRILL campus MTU. The LSP PDUs generated at a TRILL switch
could, as part of the flooding process, be sent over any adjacency in
the campus. To assure correct operation of IS-IS, an LSP PDU must be
able to reach every RBridge in the IS-IS reachable campus, which
might be impossible if the PDU exceeded the MTU of an adjacency that
was part of the campus topology.
An RBridge, RB1, determines the desired campus link MTU by
calculating the minimum of its originatingL1LSPBufferSize and the
originatingL1LSPBufferSize of other RBridges in the campus, as
advertised in the link state database, but not less than 1,470 bytes.
Although originatingL1LSPBufferSize in Layer 3 [IS-IS] is limited to
the range 512 to 1,492 bytes inclusive, in TRILL it is limited to the
range 1,470 to 65,535 bytes inclusive. (See Section 5 of [RFCclear].)
Although MTU testing is optional, it is mandatory for an RBridge to
respond to an MTU-probe PDU with an MTU-ack PDU [RFC6325]
[RFC6326bis]. Use of multicast or unicast for MTU-probe and MTU-ack
is an implementation choice. However, the burden on the link is
generally minimized by the following: (1) multicasting MTU-probes
when a response from all other RBridges on the link is desired, such
as when initializing or re-confirming MTU, (2) unicasting MTU-probes
when a response from a single RBridge is desired, such as one that
has just been detected on the link, and (3) unicasting all MTU-ack
packets.
RB1 can test the MTU size to RB2 as described in Section 4.3.2 of
[RFC6325]. For this purpose, MTU testing is only done in the
Designated VLAN. An adjacency that fails the MTU test at the campus
MTU will not enter the Report state or, if the adjacency is in that
state, it leaves that state. Thus, an adjacency failing the MTU test
at the campus minimum MTU will not be reported by the RBridge
performing the test. Since inclusion in least-cost route computation
requires the adjacency to be reported by both ends, as long as the
RBridge at either end of the adjacency notices the MTU failure, it
will not be so used.
If it tests MTU size, RB1 reports the largest size for which the MTU
test succeeds or a flag indicating that it fails at the campus MTU.
This report always appears with the neighbor in RB1's TRILL Neighbor
TLV. RB1 MAY also report this with the adjacency in an Extended
Reachability TLV in RB1's LSP. RB1 MAY choose to test MTU sizes
greater than the desired campus MTU as well as the desired campus
MTU.
Most types of TRILL IS-IS packets, such as LSPs, can make use of the
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INTERNET-DRAFT TRILL: Adjacency
campus MTU. The exceptions are TRILL Hellos, which must be kept
small for loop safety, and the MTU PDUs, whose size must be adjusted
appropriately for the tests being performed.
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6. BFD Enabled and BFD Session Bootstrap
When the adjacency between RBridges reaches the 2-Way state, TRILL
Hellos will already have been exchanged. If an RBridge supports BFD
[RFCbfd] it will have learned whether the other RBridge has BFD
enabled by whether or not a BFD Enabled TLV [RFC6213] was included in
its Hellos. In addition, TRILL Hellos include a nickname of the
sending RBridge [RFC6326bis] so that information will be available to
the receiving RBridge.
The BFD Enabled TLVs in TRILL Hellos will look like the following:
+-+-+-+-+-+-+-+-+
| Type=148 | (1 bytes)
+-+-+-+-+-+-+-+-+
| Length=3*n | (1 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RESV | MTID=0 | (2 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NLPID=0xC0 | (1 bytes)
+-+-+-+-+-+-+-+-+-+-+-...
| possible additional (3*(n-1) bytes)
| topology/NLPID pairs
+-+-+-+-+-+-+-...
Figure 3. BFD Enabled TLV Example/Format
Type = 148 for BFD Enabled [RFC6213].
Length will be 3 times the number of topology and protocol
pairs in the TLV.
MTID is a topology ID [RFC5120] that will be zero unless multi-
topology is being supported [MT].
NLPID is a Network Layer Protocol ID [RFC6328] and will be 0xC0
for TRILL. but additional topology and protocol pairs could
conceivably be listed.
An RBridge port initiates a one-hop BFD session with another RBridge
if the following conditions are met: (1) it has BFD enabled, (2) it
has an adjacency to another RBridge in the 2-way or Report state, and
(3) the Hellos it receives indicate that the other RBridge also has
BFD enabled. Either (a) BFD was enabled on both RBridge ports when
the adjacency changed to the 2-way or Report state or (b) the
adjacency was already in 2-way or Report state and BFD was enabled on
one RBridge port when BFD had been enabled on the other or (c) BFD
was simultaneously enabled on both RBridge ports.
In such a BFD session, BFD is encapsulated as specified in [RFCbfd].
D. Eastlake, et al [Page 25]
INTERNET-DRAFT TRILL: Adjacency
The egress nickname to be used will have been learned from received
Hellos. On a point-to-point link, the Any-RBridge nickname [RFCclear]
can also be used as egress since support of that nickname is required
by support of RBridge Channel [RFCchannel] and support of RBridge
Channel is required for support of BFD over TRILL.
The rare case of transient nickname conflict (due to the network
operator configuring a conflict, connectivity appearing to a
previously isolated RBridge, or the like) can cause transient failure
of an ongoing BFD session. This can be avoided in the one-hop point-
to-point case by using the Any-RBridge egress nickname. In cases
where Any-RBridge cannot be used as the egress nickname and a
transient nickname conflict is detected for the intended destination
of a BFD session, initiation of the session SHOULD be delayed until
the conflict is resolved.
If a one-hop BFD session is initiated when the adjacency is in the
2-way state, the adjacency MUST NOT advance to the Report state until
BFD and any other enabled connectivity test (including MTU if
enabled) have succeeded, as specified in Section 3.
If a one-hop BFD session is established when the adjacency is in the
Report state, due to enablement at the RBridges, then, to minimize
unnecessary topology changes, the adjacency MUST remain in the Report
state unless and until the BFD session (or some other enabled
connectivity test) fails.
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7. Pseudonodes
This section only applies to broadcast links as there is no DRB and
there cannot be a pseudonode [IS-IS] for a link configured as point-
to-point. The Designated RBridge (DRB), determined as described
above, controls whether a pseudonode will be used on a link.
If the DRB sets the bypass pseudonode bit in its TRILL LAN Hellos,
the RBridges on the link (including the DRB) just directly report all
their adjacencies on the LAN that are in the Report state. If the
DRB does not set the bypass pseudonode bit in its TRILL Hellos, then
(1) the DRB reports in its LSP its adjacency to the pseudonode, (2)
the DRB sends LSPs on behalf of the pseudonode in which it reports
adjacency to all other RBridges on the link where it sees that
adjacency in the Report state, and (3) all other RBridges on the link
report their adjacency to the pseudonode if they see their adjacency
to the DRB as being in the Report state and do not report any other
adjacencies on the link. Setting the bypass pseudonode bit has no
effect on how LSPs are flooded on a link. It only affects what LSPs
are generated.
It is anticipated that many links between RBridges will actually be
point-to-point even in cases where the link technology supports
operation as a multi-access broadcast link, in which case using a
pseudonode merely adds to the complexity. For example, if RB1 and
RB2 are the only RBridges on the link, and RB1 is DRB, then if RB1
creates a pseudonode that is used, there are 3 LSPs: for, say, RB1.25
(the pseudonode), RB1, and RB2, where RB1.25 reports connectivity to
RB1 and RB2, and RB1 and RB2 each just say they are connected to
RB1.25. Whereas if DRB RB1 sets the bypass pseudonode bit in its
Hellos, then there will be only 2 LSPs: RB1 and RB2 each reporting
connectivity to each other.
A DRB SHOULD set the bypass pseudonode bit in its Hellos if it has
not seen at least two simultaneous adjacencies in the Report state
since it last rebooted or was reset by network management.
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8. More TRILL Hello Details
This section provides further details on the receipt, transmission,
and content of TRILL Hellos. Unless otherwise stated, it applies to
both LAN and point-to-point Hellos.
TRILL Hellos, like all TRILL IS-IS packets, are primarily
distinguished from Layer 3 IS-IS packets on Ethernet by being sent to
the All-IS-IS-RBridges multicast address (01-80-C2-00-00-41). TRILL
IS-IS packets on Ethernet also have the L2-IS-IS Ethertype (0x22F4)
and are Ethertype encoded.
Although future extensions to TRILL may include use of Level 2 IS-IS,
[RFC6325] specifies TRILL using a single Level 1 Area using the fixed
Area Address zero (see Section 4.2 of [RFC6326bis]).
IS-IS Layer 3 routers are frequently connected to other Layer 3
routers that are part of a different routing domain. In that case,
the externalDomain flag (see [IS-IS]) is normally set for the port
through which such a connection is made. The setting of this flag to
"true" causes no IS-IS PDUs to be sent out the port and any IS-IS
PDUs received to be discarded, including Hellos. RBridges operate in
a different environment where all neighbor RBridges merge into a
single campus. For loop safety, RBridges do not implement the
externalDomain flag or implement it with the fixed value "false".
They send and can receive TRILL Hellos on every port that is not
disabled.
8.1 Contents of TRILL Hellos
The table below lists mandatory (M) and optional (O) content TLVs for
TRILL Hellos that are particularly relevant to this document,
distinguishing between TRILL LAN Hellos and TRILL P2P Hellos. A "-"
indicates that an occurrence would be ignored. There are additional
TLVs and sub-TLVs that can occur in TRILL Hellos [RFC6326bis].
D. Eastlake, et al [Page 28]
INTERNET-DRAFT TRILL: Adjacency
LAN P2P Numb Content Item
--- --- ---- ------------
M M 1 Area Addresses TLV with area zero only
M M 1 MT Port Capabilities TLV containing a VLAN-FLAGs
sub-TLV
O O 0-n Other MT Port Capability TLVs
M - 0-n TRILL Neighbor TLV (see Section 8.2.1)
- M 1 Three-Way Handshake TLV
O O 0-n Protocols Supported TLV that MUST list the TRILL
NLPID (0xC0) [RFC6328]
O O 0-1 BFD Enabled TLV
O O 0-1 Authentication TLV
- - 0-n Padding TLV, SHOULD NOT be included
Table 4. TRILL Hello Contents
A TRILL Hello MAY also contain any TLV permitted in a Layer 3 IS-IS
Hello. As with all IS-IS PDUs, TLVs that are unsupported/unknown in
TRILL Hellos are ignored.
8.2 Transmitting TRILL Hellos
TRILL Hellos are sent with the same timing as Layer 3 IS-IS Hellos
[IS-IS]; however, no Hellos are sent if a port is in the Suspended or
Down states or if the port is disabled.
TRILL Hello PDUs SHOULD NOT be padded and MUST NOT be sent exceeding
1,470 bytes; however, a received TRILL Hello longer than 1,470 bytes
is processed normally.
TRILL Hello PDU headers MUST conform to the following:
o Maximum Area Addresses equal to 1.
o Circuit Type equal to 1.
See Section 8.1 for mandatory and some optional Hello TLV contents.
8.2.1 TRILL Neighbor TLVs
A TRILL Neighbor TLV SHOULD NOT be included in TRILL point-to-point
Hellos as it MUST be ignored in that context and wastes space.
TRILL Neighbor TLVs sent in a LAN Hello on an Ethernet link MUST show
the neighbor information, as sensed by the transmitting RBridge, for
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INTERNET-DRAFT TRILL: Adjacency
the VLAN on which the Hello is sent. Since implementations
conformant to this document maintain such information on a per-VLAN
basis only for the Designated VLAN, such implementations only send
the TRILL Neighbor TLV in TRILL LAN Hellos in the Designated VLAN.
It is RECOMMENDED that, if there is sufficient room, a TRILL Neighbor
TLV or TLVs, as described in Section 4.4.2.1 of [RFC6325], covering
the entire range of MAC addresses and listing all adjacencies with a
non-zero Designated VLAN Hello Holding time, or an empty list of
neighbors if there are no such adjacencies, be in TRILL Hellos sent
on the Designated VLAN. If this is not possible, then TRILL Neighbor
TLV's covering sub-ranges of MAC addresses should be sent so that the
entire range is covered reasonably promptly. Delays in sending TRILL
Neighbor TLVs will delay the advancement of adjacencies to the Report
state and the discovery of some link failures. Rapid (for example,
sub-second) detection of link or node failures is best addressed with
a protocol designed for that purpose, such as BFD (see Section 6).
To ensure that any RBridge RB2 can definitively determine whether RB1
can hear RB2, RB1's neighbor list MUST eventually cover every
possible range of IDs, that is, within a period that depends on RB1's
policy and not necessarily within any specific period such as its
Holding Time. In other words, if X1 is the smallest ID reported in
one of RB1's neighbor lists, and the "smallest" flag is not set, then
X1 MUST appear in a different neighbor list as well, as the largest
ID reported in that fragment. Or lists may overlap, as long as there
is no gap, such that some range, say between Xi and Xj, would never
appear in any list.
8.3 Receiving TRILL Hellos
Assuming a packet has the L2-IS-IS Ethertype and, if received on
Ethernet, the All-IS-IS-RBridges multicast address, it will be
examined to see if it appears to be an IS-IS PDU. If so, and it
appears to be a TRILL Hello PDU, the following tests are performed.
o The type of Hello PDU (LAN or P2P) is compared with the port
configuration. If a LAN Hello is received on a port configured
to be point-to-point or a P2P Hello is received on a port not
configured to be point-to-point, it is discarded.
o If the Circuit Type field is not 1, the PDU is discarded.
o If the PDU does not contain an Area Address TLV or it contains
an Area Address TLV that is not the single Area Address zero,
it is discarded.
o If the Hello includes a Protocols Supported TLV that does not
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list the TRILL NLPID (0xC0), it is discarded. It is acceptable
if there is no Protocols Supported TLV present.
o If the Hello does not contain an MT Port Capabilities TLV
containing a VLAN-FLAGS sub-TLV [RFC6326bis], it is discarded.
o If the maximumAreaAddresses field of the PDU is not 1, it is
discarded.
o If IS-IS authentication is in use on the link and the PDU
either has no Authentication TLV or validation of that
Authentication TLV fails, it is discarded.
If none of the rules in the list above causes the packet to be
discarded and it is parseable, it is assumed to be a well-formed
TRILL Hello received on the link. It is treated as an event A0, A1,
A2, or A3 based on the criteria listed in Section 3.3.
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9. Multiple Ports on the Same Broadcast Link
It is possible for an RBridge RB1 to have multiple ports on the same
broadcast (LAN) link that are not in the Suspended state. It is
important for RB1 to recognize which of its ports are on the same
link. RB1 can detect this condition based on receiving TRILL Hello
messages with the same LAN ID on multiple ports.
The DRB election is port-based (see Section 4) and only the Hellos
from the elected port can perform certain functions such as dictating
the Designated VLAN or whether a pseudonode will be used; however,
the election also designates the RBridge with that port as DRB for
the link. An RBridge may choose to load split some tasks among its
ports on the link if it has more than one. Section 4.4.4 of [RFC6325]
describes when it is safe to do so.
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10. Security Considerations
This memo provides improved documentation of some aspects of the
TRILL base protocol standard, particularly five aspects of the TRILL
adjacency establishment and Hello protocol as listed in Section 1.
It does not change the security considerations of the TRILL base
protocol that are in Section 6 of [RFC6325].
See [RFCbfd] for security considerations for BFD whose use in
connection with TRILL adjacency is discussed in this document,
particularly Section 6.
11. IANA Considerations
This document requires no IANA Actions. RFC Editor: Please remove
this section before publication.
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Appendix A: Changes from [RFC6327]
This document has the following changes from [RFC6327]. It obsoletes
[RFC6327].
1. Extends the TRILL Hello size limit, MTU testing, and state machine
to point-to-point links.
2. Incorporates the updates to [RFC6327] from [RFCclear].
3. The bulk of [RFC6327] was written from the point of view that
links between TRILL switches would only be Ethernet. In fact, they
could be any technology, such as PPP [RFC6361] or IP [TrillIP].
This replacement document generalizes [RFC6327] to cover such link
types.
4. Includes a specification of one-hop BFD session establishment in
connection with adjacency.
5. Numerous editorial changes.
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Appendix B: Changes to [RFC6325]
Section 2 of this document replaces Section 4.4.1 of [RFC6325] and
Section 8 of this document replaces Section 4.4.2 of [RFC6325] except
for Section 4.4.2.1. The changes in [RFC6325] made by this document
include
- Prohibiting the sending of TRILL Hellos out a port while it is
in the Suspended state and the specification of the Suspended
state. ([RFC6325] specifies Hellos to be sent with the same
timing as [IS-IS].)
- Permitting the inclusion of the Three-Way-Handshake TLV, BFD
Enabled TLV, and other TLVs in TRILL Hellos when these were
omitted in TRILL Hello contents lists in Section 4.4.2 of
[RFC6325].
- Extending the TRILL Hello protocol to support point-to-point
and non-Ethernet links.
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Appendix Z: Change History
RFC Editor Note: Please delete this section before publication.
From -00 to -01
Improvements to Section 6 related to the rare case of transient
nickname conflict.
Numerous editorial improvements and typos fixes.
Changes to Acknowledgements and author list.
From -01 to -02
Editorial improvements.
One editorial correction: deleting "or received in TRILL Hellos" from
Section 6. (If a new RBridge joins a campus on a link with an MTU
lower than the campus MTU (Sz), there might be a problem where LSPs
wouldn't get through the link and, since LSPs carry the
originatingLSPBufferSize, this might never get fixed. However, this
has been fixed in draft-ietf-isis-rfc6326bis by requiring
originatingLSPBufferSize be in LSP fragment zero and restricting the
size of LSP fragment zero to 1470 bytes so it will get through. This
snippet of text is left over from when it was thought to fix this in
a different way by including originatingLSPBufferSize in Hellos.)
Add one Acknowledgement.
From -02 to -03
Editorial improvements resulting from GENART review. Add GENART
reviewer to acknowledgements.
From -03 to -04
Clarify what this document changes in RFC 6325 and add Appendix B.
Minor editorial fixes.
D. Eastlake, et al [Page 36]
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Normative References
[IS-IS] - ISO/IEC 10589:2002, Second Edition, "Intermediate System to
Intermediate System Intra-Domain Routing Exchange Protocol for
use in Conjunction with the Protocol for Providing the
Connectionless-mode Network Service (ISO 8473)", 2002.
[RFC1195] - Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
dual environments", RFC 1195, December 1990.
[RFC2119] - Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5120] - Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
Topology (MT) Routing in Intermediate System to Intermediate
Systems (IS-ISs)", RFC 5120, February 2008.
[RFC6213] - Hopps, C. and L. Ginsberg, "IS-IS BFD-Enabled TLV", RFC
6213, April 2011.
[RFC6325] - Perlman, R., D. Eastlake, D. Dutt, S. Gai, and A.
Ghanwani, "RBridges: Base Protocol Specification", RFC 6325,
July 2011.
[RFC6328] - Eastlake 3rd, D., "IANA Considerations for Network Layer
Protocol Identifiers", BCP 164, RFC 6328, July 2011.
[RFCbfd] - Manral, V., D. Eastlake, D. Ward, A. Banerjee, "TRILL
(Transparent Interconnetion of Lots of Links): Bidirectional
Forwarding Detection (BFD) Support", draft-ietf-trill-rbridge-
bfd, in RFC Editor's queue.
[RFCchannel] - D. Eastlake, V. Manral, Y. Li, S. Aldrin, D. Ward,
"TRILL: RBridge Channel Support", draft-ietf-trill-rbridge-
channel-08.txt, in RFC Editor's queue.
[RFCclear] - Eastlake, D., M. Zhang, A. Ghanwani, V. Manral, A.
Banerjee, "TRILL: Clarifications, Corrections, and Updates "
draft-ietf-trill-clear-correct, in RFC Editor's queue.
[RFC6326bis] - Eastlake, D., Banerjee, A., Dutt, D., Perlman, R., and
A. Ghanwani, "TRILL Use of IS-IS", draft-ietf-isis-rfc6326bis,
work in progress.
Informative References
[802.1AX] - "IEEE Standard for Local and metropolitan area networks /
Link Aggregation", 802.1AX-2008, 1 January 2008.
D. Eastlake, et al [Page 37]
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[802.1Q] - "IEEE Standard for Local and metropolitan area networks /
Media Access Control (MAC) Bridges and Virtual Bridge Local
Area Networks", 802.1Q-2011, 31 August 2011.
[FCoE] - From www.t11.org discussion of "FCoE Max Size" generated
from T11/09-251v1, 04/27/2009, "FCoE frame or FCoE PDU".
[MT] - D. Eastlake, M. Zhang, A. Banerjee, V. Manral, "TRILL: Multi-
Topology", draft-eastlake-trill-multi-topology, work in
progress.
[RFC3719] - Parker, J., Ed., "Recommendations for Interoperable
Networks using Intermediate System to Intermediate System (IS-
IS)", February 2004.
[RFC6327] - Eastlake 3rd, D., Perlman, R., Ghanwani, A., Dutt, D.,
and V. Manral, "Routing Bridges (RBridges): Adjacency", RFC
6327, July 2011.
[RFC6361] - Carlson, J. and D. Eastlake 3rd, "PPP Transparent
Interconnection of Lots of Links (TRILL) Protocol Control
Protocol", RFC 6361, August 2011.
[RFC6439] - Perlman, R., Eastlake, D., Li, Y., Banerjee, A., and F.
Hu, "Routing Bridges (RBridges): Appointed Forwarders", RFC
6439, November 2011.
[RFCfgl] - D. Eastlake, M. Zhang, P. Agarwal, R. Perlman, D. Dutt,
"TRILL (Transparent Interconnection of Lots of Links): Fine-
Grained Labeling", draft-ietf-trill-fine-labeling, in RFC
Editor's queue.
[ESADI] - Zhai, H., F. Hu, R. Perlman, D. Eastlake, O. Stokes, "
TRILL (Transparent Interconnection of Lots of Links): ESADI
(End Station Address Distribution Information) Protocol",
draft-ietf-trill-esadi, work in progress.
[TrillIP] - M. Wasserman, D. Eastlake, D. Zhang, "Transparent
Interconnection of Lots of Links (TRILL) over IP", draft-mrw-
trill-over-ip, work in progress.
D. Eastlake, et al [Page 38]
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Acknowledgements
The suggestions and comments of the following are gratefully
acknowledged:
Stewart Bryant, Elwyn Davies, Adrian Farrel, Brian Haberman, Jon
Hudson, Arnel Lim, and Gayle Noble
The authors of [RFC6327] included Dinesh Dutt and the
acknowledgements section of [RFC6327] includes the following listed
in alphabetic order: Jari Arkko, Ayan Banerjee, Les Ginsberg, Sujay
Gupta, David Harrington, Pete McCann, Erik Nordmark, and Mike Shand.
The document was prepared in raw nroff. All macros used were defined
within the source file.
D. Eastlake, et al [Page 39]
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Authors' Addresses
Donald E. Eastlake, 3rd
Huawei Technologies
155 Beaver Street
Milford, MA 01757 USA
Phone: +1-508-333-2270
EMail: [email protected]
Radia Perlman
Intel Labs
2200 Mission College Blvd.
Santa Clara, CA 95054-1549 USA
Phone: +1-408-765-8080
EMail: [email protected]
Anoop Ghanwani
Dell
350 Holger Way
San Jose, CA 95134 USA
Phone: +1-408-571-3500
EMail: [email protected]
Howard Yang
Cisco Systems
170 West Tasman Drive
San Jose, CA 95134 USA
Email: [email protected]
Vishwas Manral
Hewlett Packard Co.
19111 Pruneridge Ave,
Cupertino, CA 95014 USA
Phone: +1-408-447-1497
EMail: [email protected]
D. Eastlake, et al [Page 40]
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D. Eastlake, et al [Page 41]