Internet Engineering Task Force (IETF) D. Eastlake 3rd

Internet Engineering Task Force (IETF) D. Eastlake 3rd
Request for Comments: 7178 Huawei
Category: Standards Track V. Manral
ISSN: 2070-1721 Ionos Corp.
Y. Li
S. Aldrin
Huawei
D. Ward
Cisco
May 2014

Transparent Interconnection of Lots of Links (TRILL):
RBridge Channel Support

Abstract

This document specifies a general channel mechanism for sending
messages, such as Bidirectional Forwarding Detection (BFD) messages,
between Routing Bridges (RBridges) and between RBridges and end
stations in an RBridge campus through extensions to the Transparent
Interconnection of Lots of Links (TRILL) protocol.

Status of This Memo

This is an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.

Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7178.

Eastlake, et al. Standards Track [Page 1]

RFC 7178 TRILL: RBridge Channel Support May 2014

Copyright Notice

Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.

This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.

Table of Contents

1. Introduction ....................................................3
1.1. RBridge Channel Requirements ...............................3
1.2. Relation to the MPLS Generic Associated Channel ............4
1.3. Terminology ................................................4
2. Inter-RBridge Channel Messages ..................................4
2.1. RBridge Channel Message Inner Frame ........................6
2.1.1. RBridge Channel Header ..............................6
2.1.2. Inner Ethernet Header ...............................8
2.1.3. Inner.VLAN Tag ......................................8
2.2. TRILL Header for RBridge Channel Messages ..................9
2.3. Ethernet Link Header and Trailer ..........................10
2.4. Special Transmission and Rate Considerations ..............10
3. Processing RBridge Channel TRILL Data Messages .................11
3.1. Processing the RBridge Channel Header .....................12
3.2. RBridge Channel Errors ....................................13
4. Native RBridge Channel Frames ..................................14
5. Indicating Support for RBridge Channel Protocols ...............16
6. Congestion Considerations ......................................16
7. Allocation Considerations ......................................17
7.1. IANA Considerations .......................................17
7.2. IEEE Registration Authority Considerations ................18
8. Security Considerations ........................................18
9. References .....................................................19
9.1. Normative References ......................................19
9.2. Informative References ....................................20
10. Acknowledgments ...............................................20

Eastlake, et al. Standards Track [Page 2]

RFC 7178 TRILL: RBridge Channel Support May 2014

1. Introduction

RBridge campuses provide transparent least-cost forwarding using the
Transparent Interconnection of Lots of Links (TRILL) protocol that
builds on Intermediate System to Intermediate System (IS-IS) routing
[IS-IS] [RFC1195] [RFC7176]. Devices that implement TRILL are called
Routing Bridges (RBridges) or TRILL Switches. However, the TRILL
base protocol standard [RFC6325] provides only for TRILL Data
messages and TRILL IS-IS messages.

This document specifies a general channel mechanism for the
transmission of other messages within an RBridge campus, such as BFD
[RFC5880] messages, (1) between RBridges and end stations that are
directly connected on the same link and (2) between RBridges. This
mechanism supports a requirement to be able to operate with minimal
configuration.

1.1. RBridge Channel Requirements

It is anticipated that various protocols operating at the TRILL layer
will be desired in RBridge campuses. For example, there is a need
for rapid-response continuity checking with a protocol such as BFD
[RFC5880] [RFC5882] and for a variety of optional reporting.

To avoid the requirement to design and specify a way to carry each
such protocol, this document specifies a general channel for sending
messages between RBridges in a campus at the TRILL level by extending
the TRILL protocol. To accommodate a wide variety of protocols, this
RBridge Channel facility accommodates all the regular modes of TRILL
Data transmission including single- and multiple-hop unicast as well
as VLAN-scoped multi-destination distribution.

To minimize any unnecessary burden on transit RBridges and to provide
a more realistic test of network continuity and the like, RBridge
Channel messages are designed to look like TRILL Data frames and, in
the case of multi-hop messages, can normally be handled by transit
RBridges as if they were TRILL Data frames; however, to enable
processing at transit RBridges when required by particular messages,
they may optionally use the RBridge Channel Alert TRILL extended
header flags [RFC7179] that causes a transit RBridge implementing the
flag to more closely examine a flagged frame.

This document also specifies a format for sending RBridge Channel
messages between RBridges and end stations that are directly
connected over a link, in either direction, when provided for by the
protocol involved. For the most part, this format is the same as the
format that is encapsulated by TRILL Data for inter-RBridge Channel
messages.

Eastlake, et al. Standards Track [Page 3]

RFC 7178 TRILL: RBridge Channel Support May 2014

Each particular protocol using the RBridge Channel facility will
likely use only a subset of the facilities specified herein.

1.2. Relation to the MPLS Generic Associated Channel

The RBridge Channel is similar to the MPLS Generic Associated Channel
specified in [RFC5586]. Instead of using a special MPLS label to
indicate a special channel message, an RBridge Channel message is
indicated by a special multicast Inner.MacDA and inner Ethertype (see
Section 2.1).

1.3. Terminology

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].

The terminology and acronyms of [RFC6325] are used in this document
with the additions listed below.

BFD - Bidirectional Forwarding Detection

CHV - Channel Header Version

MH - Multi-Hop

NA - Native

SL - Silent

2. Inter-RBridge Channel Messages

Channel messages between RBridges are transmitted as TRILL Data
frames. (For information on channel messages that can be transmitted
between RBridges and end stations that are directly connected by a
link, see Section 4.) Inter-RBridge Channel messages are identified
as such by their Inner.MacDA, which is the All-Egress-RBridges
multicast address, together with their inner Ethertype, which is the
RBridge-Channel Ethertype. This Ethertype is part of and starts the
RBridge Channel Header.

Eastlake, et al. Standards Track [Page 4]

RFC 7178 TRILL: RBridge Channel Support May 2014

The diagram below shows the overall structure of an RBridge Channel
Message frame on a link between two RBridges:

Frame Structure Section of This Document
------------------------
+--------------------------------+
| Link Header | Section 2.3 if Ethernet link
+--------------------------------+
| TRILL Header | Section 2.2
+--------------------------------+
| Inner Ethernet Header | Section 2.1.2
+--------------------------------+
| RBridge Channel Header | Section 2.1.1
+--------------------------------+
| Protocol-Specific Payload | See specific channel protocol
+--------------------------------+
| Link Trailer (FCS if Ethernet) |
+--------------------------------+

Figure 1: RBridge Channel Frame Structure

Optionally, some channel messages may require examination of the
frame by transit RBridges that support the RBridge Channel feature,
to determine if they need to take any action. To indicate this, such
messages use an RBridge Channel Alert extended TRILL Header flag as
further described in Section 3 below.

Sections 2.1 and 2.2 describe the inner frame and the TRILL Header
for frames sent in an RBridge Channel. As always, the outer Link
Header and Link Trailer are whatever is needed to get a TRILL Data
frame to the next-hop RBridge, depending on the technology of the
link, and can change with each hop for multi-hop messages. Section
2.3 describes the outer Link Header for Ethernet links, and Section
2.4 discusses some special considerations for the first hop
transmission of RBridge Channel messages.

Section 3 describes some details of RBridge Channel message
processing. Section 4 provides the specifications for native RBridge
Channel frames between RBridges and end stations that are directly
connected over a link. Section 5 describes how support for RBridge
Channel protocols is indicated. And Sections 6, 7, and 8 give
congestion, allocation (IANA and IEEE), and security considerations
respectively.

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RFC 7178 TRILL: RBridge Channel Support May 2014

2.1. RBridge Channel Message Inner Frame

The encapsulated inner frame within an RBridge Channel message frame
is as shown below.

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
Inner Ethernet Header:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Special Inner.MacDA = All-Egress-RBridges |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Special Inner.MacDA cont. | Inner.MacSA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Inner.MacSA cont. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| VLAN Tag Ethertype | Priority, DEI, VLAN ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
RBridge Channel Header:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RBridge-Channel Ethertype | CHV | Channel Protocol |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | ERR |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Information specific to the RBridge Channel Protocol:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Channel-Protocol-Specific Data
| ...

Figure 2: RBridge Channel Inner Frame Header Fields

The Channel-Protocol-Specific Data contains the information related
to the specific channel protocol used in the channel message.
Details of that data are outside the scope of this document, except
in the case of the RBridge Channel Error protocol specified in
Section 3.2.

2.1.1. RBridge Channel Header

As shown in Figure 2, the RBridge Channel Header starts with the
RBridge-Channel Ethertype (see Section 7.2). Following that is a
four-byte quantity with four sub-fields as follows:

CHV: A 4-bit field that gives the RBridge Channel Header Version.
This document specifies version zero.

Eastlake, et al. Standards Track [Page 6]

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Channel Protocol: A 12-bit unsigned integer that specifies the
particular RBridge Channel protocol to which the message
applies.

Flags: Provides 12 bits of flags as described below.

ERR: A 4-bit unsigned integer used in connection with error
reporting at the RBridge Channel level as described in Section
3.

The flag bits are numbered from 0 to 11 as shown below.

| 0 1 2 3 4 5 6 7 8 9 10 11|
+--+--+--+--+--+--+--+--+--+--+--+--+
|SL|MH|NA| Reserved |
+--+--+--+--+--+--+--+--+--+--+--+--+

Figure 3: Channel Header Flag Bits

Bit 0: The SL or Silent bit, the high-order bit in network order.
If it is a one, it suppresses RBridge Channel Error messages
(see Section 3).

Bit 1: The MH or Multi-Hop bit. It is used to inform the
destination RBridge protocol that the message may be multi-hop
(MH=1) or was intended to be one-hop only (MH=0).

Bit 2: The NA or Native bit. It is used as described in Section
4.

Reserved: Bits reserved for future specification that MUST be sent
as zero and ignored on receipt.

The RBridge Channel Protocol field specifies the protocol that the
channel message relates to. The initial defined value is listed
below.

Protocol Name - Section of This Document
-------- -------------------------------
0x001 RBridge Channel Error - Section 3

IANA Considerations for RBridge Channel protocol numbers are provided
in Section 7. These include provisions for Private Use protocol
numbers. Because different uses of Private Use RBridge Channel
protocol numbers may conflict, such use MUST be within a private
network. It is the responsibility of the private network manager to
avoid conflicting use of these code points and unacceptable burdens
within the private network from their use.

Eastlake, et al. Standards Track [Page 7]

RFC 7178 TRILL: RBridge Channel Support May 2014

2.1.2. Inner Ethernet Header

The special Inner.MacDA is the All-Egress-RBridges multicast Media
Access Control (MAC) address to signal that the frame is intended for
the egress (decapsulating) RBridge itself (or the egress RBridges
themselves if the frame is multi-destination). (This address is
called the All-ESADI-RBridges address in [RFC6325].) The RBridge-
Channel Ethertype indicates that the frame is an RBridge Channel
message. The only other Ethertype currently specified for use with
the All-Egress-RBridges Inner.MacDA is L2-IS-IS to indicate an ESADI
frame [RFC6325]. In the future, additional Ethertypes may be
specified for use with the All-Egress-RBridges multicast address.

The RBridge originating the channel message selects the Inner.MacSA.
The Inner.MacSA MUST be set by the originating RBridge to a MAC
address unique within the campus owned by the originating RBridge.
This MAC address can be considered, in effect, the MAC address of a
virtual internal end station that handles the RBridge Channel frames
originated by or destined for that RBridge. It MAY be the same as
the Inner.MacSA used by the RBridge when it originates ESADI frames
[RFC6325].

2.1.3. Inner.VLAN Tag

As with all frames formatted to be processed as a TRILL Data frame,
an Inner.VLAN tag is present. Use of a VLAN tag Ethertype other than
0x8100 or stacked tags is beyond the scope of this document but is an
obvious extension.

Multi-destination RBridge Channel messages are, like all multi-
destination TRILL Data messages, VLAN scoped so the Inner.VLAN ID
MUST be set to the VLAN of interest. To the extent that distribution
tree pruning is in effect in the campus, such channel messages may
only reach RBridges advertising that they have connectivity to that
VLAN.

For channel messages sent as known unicast TRILL Data frames, the
default value for the Inner.VLAN ID is VLAN 1, but particular RBridge
Channel protocols MAY specify other values.

The Inner.VLAN also specifies a three-bit frame priority for which
the following recommendations apply:

1. For one-hop channel messages critical to network connectivity,
such as one-hop BFD for rapid link-failure detection in support
of TRILL IS-IS, the RECOMMENDED priority is 7.

Eastlake, et al. Standards Track [Page 8]

RFC 7178 TRILL: RBridge Channel Support May 2014

2. For single and multi-hop unicast channel messages important to
network operation but not critical for connectivity, the
RECOMMENDED priority is 6.

3. For other unicast channel messages and all multi-destination
channel messages, it is RECOMMENDED that the default priority
zero be used. In any case, priorities higher than 5 SHOULD NOT
be used for such frames.

There is one additional bit in a VLAN tag value between the 12-bit
VLAN ID and 3-bit priority, the Drop Eligibility Indicator (DEI)
[RFC7180]. It is RECOMMENDED that this bit be zero for the first two
categories of channel messages listed immediately above. The setting
of this bit for channel messages in the third category may be
dependent on the channel protocol and no general recommendation is
made for that case.

2.2. TRILL Header for RBridge Channel Messages

After the outer Link Header (that, for an Ethernet link, ends with
the TRILL Ethertype) and before the encapsulated frame, the channel
message's TRILL Header initially appears as follows:

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|V=0| R |M| Op-Len | Hop Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Egress Nickname | Ingress Nickname |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 4: RBridge Channel TRILL Header Fields

The TRILL Header version (V) MUST be zero; the R bits are reserved;
the M bit is set appropriately as the channel message is to be
forwarded as known destination unicast (M=0) or multi-destination
(M=1), regardless of the fact that the Inner.MacDA is always the All-
Egress-RBridges multicast address; and Op-Len is set appropriately
for the length of the TRILL Header extensions area, if any, all as
specified in [RFC6325].

When an RBridge Channel message is originated, the Hop Count field
defaults to the maximum value, 0x3F, but particular RBridge Channel
protocols MAY specify other values. For messages sent a known number
of hops, such as one-hop messages or a two-hop self-addressed message
intended to loop back through an immediate neighbor RBridge, setting
the Hop Count field in the TRILL Header to the maximum value and
checking its value on receipt provides an additional validity check

Eastlake, et al. Standards Track [Page 9]

RFC 7178 TRILL: RBridge Channel Support May 2014

as discussed in [RFC5082], where this type of field is referred to as
"TTL" or "Hop Limit".

The RBridge originating a channel message places a nickname that it
holds in the Ingress Nickname field.

There are several cases for the Egress Nickname field. If the
channel message is multi-destination, then the Egress Nickname
designates the distribution tree to use. If the channel message is a
multi-hop unicast message, then the Egress Nickname is a nickname of
the target RBridge; this includes the special case of a message
intended to loop back from an immediate neighbor where the originator
places one of its own nicknames in both the Ingress Nickname and
Egress Nickname fields. If the channel message is a one-hop unicast
message, there are two possibilities for the Egress Nickname.

o The Egress Nickname can be set to a nickname of the target
neighbor RBridge.

o The special nickname Any-RBridge may be used. RBridges supporting
the RBridge Channel facility MUST recognize the Any-RBridge
special nickname and accept TRILL Data frames having that value in
the Egress Nickname field as being sent to them as the egress.
Thus, for such RBridges, using this egress nickname guarantees
processing by an immediate neighbor regardless of the state of
nicknames.

2.3. Ethernet Link Header and Trailer

An RBridge Channel frame has the usual Link Header and Link Trailer
for a TRILL Data frame depending on the type of link on which it is
sent.

For an Ethernet link [RFC6325], the Outer.MacSA is the MAC address of
the port from which the frame is sent. The Outer.MacDA is the MAC
address of the next-hop RBridge port for unicast RBridge Channel
messages or the All-RBridges multicast address for multi-destination
RBridge Channel messages. The Outer.VLAN tag specifies the
designated VLAN for that hop, and the priority should be the same as
in the Inner.VLAN tag; however, the output port may have been
configured to strip VLAN tags, in which case no Outer.VLAN tag
appears on the wire. And the Link Trailer is the Ethernet FCS.

2.4. Special Transmission and Rate Considerations

If a multi-hop RBridge Channel message is received by an RBridge, the
criteria and method of forwarding it are the same as for any TRILL
Data frame. If it is so forwarded, it will be on a link that was

Eastlake, et al. Standards Track [Page 10]

RFC 7178 TRILL: RBridge Channel Support May 2014

included in the routing topology because it was in the Report state
as specified in [RFC7177].

However, special considerations apply to single-hop messages because,
for some RBridge Channel protocols, it may be desirable to send
RBridge Channel messages over a link that is not yet fully up. In
particular, it is permissible, if specified by the particular channel
protocol, for the source RBridge that has created an RBridge Channel
message to attempt to transmit it to a next-hop RBridge when the link
is in the Detect or 2-Way state, as specified in [RFC7177], as well
as when it is in the Report state. Such messages can also be sent on
point-to-point links that are not in the Up state.

RBridge Channel messages represent a burden on the RBridges, and
links in a campus and should be rate limited, especially if they are
sent as high priority, multi-destination, or multi-hop frames or have
an RBridge Channel Alert extended header flag set. See Section 6,
"Congestion Considerations".

3. Processing RBridge Channel TRILL Data Messages

RBridge Channel TRILL Data messages are designed to look like and, to
the extent practical, be forwarded as regular TRILL Data frames. On
receiving a channel message, an RBridge performs the usual initial
tests on the frame and makes the same forwarding and/or decapsulation
decisions as for a regular TRILL Data frame [RFC6325] with the
following exceptions for RBridges implementing the RBridge Channel
facility:

1. An RBridge implementing the RBridge Channel facility MUST
recognize the Any-RBridge egress nickname in TRILL Data frames,
decapsulating such frames if they meet other checks. (Such a
frame cannot be a valid multi-destination frame because the Any-
RBridge nickname is not a valid distribution tree root.)

2. If an RBridge Channel Alert extended header flag is set, then the
RBridge MUST process the RBridge Channel message as described
below even if it is not egressing the frame. If it is egressing
the frame, then no additional processing beyond egress processing
is needed even if an RBridge Channel Alert flag is set.

3. On decapsulation, the special Inner.MacDA value of All-Egress-
RBridges MUST be recognized to trigger checking the
Inner.Ethertype and processing as an RBridge Channel message if
that Ethertype is RBridge-Channel.

Eastlake, et al. Standards Track [Page 11]

RFC 7178 TRILL: RBridge Channel Support May 2014

RBridge Channel messages SHOULD only be sent to RBridges that
advertise support for the channel protocol involved as described in
Section 5.

All RBridges supporting the RBridge Channel facility MUST recognize
the RBridge-Channel inner Ethertype.

3.1. Processing the RBridge Channel Header

Knowing that it has an RBridge Channel message, the egress RBridge,
and any transit RBridge if an RBridge Channel Alert bit is set in the
TRILL Header, looks at the CHV (RBridge Channel Header Version) and
Channel Protocol fields.

If any of the following conditions occur at an egress RBridge, the
frame is not processed, an error may be generated as specified in
Section 3.2, and the frame is discarded. The behavior is the same if
the frame is being processed at a transit RBridge because the RBridge
Critical Channel Alert flag is set [RFC7179]. However, if these
conditions are detected at a transit RBridge examining the message
because the RBridge Non-critical Channel Alert flag is set [RFC7179]
but the RBridge Critical Channel Alert flag is not set, no error is
generated, and the frame is still forwarded normally.

Error Conditions:

1. The Ethertype is not RBridge-Channel and not any other Ethertype
known to the RBridge as usable with the All-Egress-RBridges
Inner.MacDA, or the frame is so short that the Ethertype is
truncated.

2. The CHV field is non-zero, or the frame is so short that the
version zero Channel Header is truncated.

3. The Channel Protocol field is a reserved value or a value unknown
to the processing RBridge.

4. The ERR field is non-zero, and Channel Protocol is a value other
than 0x001.

5. The RBridge Channel Header NA flag is set to one, indicating that
the frame should have been received as a native frame rather than
a TRILL Data frame.

If the CHV field and NA flag are zero and the processing RBridge
recognizes the Channel Protocol value, it processes the message in
accordance with that channel protocol. The processing model is as if
the received frame starting with and including the TRILL Header is

Eastlake, et al. Standards Track [Page 12]

RFC 7178 TRILL: RBridge Channel Support May 2014

delivered to the Channel protocol along with a flag indicating
whether this is (a) transit RBridge processing due to an RBridge
Channel Alert flag being set or (b) egress processing.

Errors within a recognized Channel Protocol are handled by that
channel protocol itself and do not produce RBridge Channel Error
frames.

3.2. RBridge Channel Errors

A variety of problems at the RBridge Channel level cause the return
of an RBridge Channel Error frame unless one of the following apply:
(a) the "SL" (Silent) flag is a one in the channel message for which
the problem was detected, (b) the processing is due to the RBridge
Non-critical Channel Alert flag being set, (c) the frame in error
appears, itself, to be an RBridge Channel Error frame (has a non-zero
ERR field or a Channel Protocol of 0x001), or (d) the error is
suppressed due to rate limiting.

An RBridge Channel Error frame is a multi-hop unicast RBridge Channel
message with the Ingress Nickname set to a nickname of the RBridge
detecting the error and the Egress Nickname set to the value of the
Ingress Nickname in the channel message for which the error was
detected. No per-hop transit processing is specified for such error
frames, so the RBridge Channel Alert extended header flags SHOULD, if
an extension is present, be set to zero. The SL and MH flags SHOULD
be set to one; the NA flag MUST be zero; and the ERR field MUST be
non-zero as described below. For the protocol-specific data area, an
RBridge Channel Message Error frame has at least the first 256 bytes
(or less if less are available) of the erroneous decapsulated channel
message starting with the TRILL Header. (Note: The TRILL Header does
not include the TRILL Ethertype that is part of the Link Header on
Ethernet links.)

The following values for ERR are specified:

ERR RBridge Channel Error Code Meaning
--- ----------------------------------
0 No error
1 Frame too short (truncated Ethertype or Channel Header)
2 Unrecognized Ethertype
3 Unimplemented value of CHV
4 Wrong value of NA flag
5 Channel Protocol is reserved or unimplemented
6-14 Unassigned (see Section 7)
15 Reserved (see Note)

Eastlake, et al. Standards Track [Page 13]

RFC 7178 TRILL: RBridge Channel Support May 2014

Note: Intended to be allocated by Standards Action for an error
code expansion feature when it appears likely that all
other available error codes are being allocated.

All RBridges implementing the RBridge Channel feature MUST recognize
the RBridge Channel Error protocol value (0x001). They MUST NOT
generate an RBridge Channel Error message in response to an RBridge
Channel Error message, that is, a channel message with a protocol
value of 0x001 or with a non-zero ERR field.

4. Native RBridge Channel Frames

Other sections of this document specify non-native RBridge Channel
messages and their processing, that is, RBridge Channel messages
formatted as TRILL Data frames and sent between RBridges. This
section specifies the differences for native RBridge Channel
messages.

If provided for by the channel protocol involved, native RBridge
Channel messages may be sent between end stations and RBridges that
are directly connected over a link, in either direction. On an
Ethernet link, such native frames have the RBridge-Channel Ethertype
and are like the encapsulated frame inside an RBridge Channel message
except as follows:

1. TRILL does not require the presence of a VLAN tag on such native
RBridge Channel frames. However, port configuration, link
characteristics, or the channel protocol involved may require
such tagging.

2. If the frame is unicast, the destination MAC address is the
unicast MAC address of the RBridge or end-station port that is
its intended destination. If the frame is multicast by an end
station to all the RBridges on a link that support an RBridge
Channel protocol using this transport, the destination MAC
address is the All-Edge-RBridges multicast address (see Section
7). A native RBridge Channel frame received at an ingress
RBridge is discarded if its destination MAC address is neither
the unicast address of the port nor the multicast address All-
Edge-RBridges. If the frame is multicast by an RBridge to all
the devices that TRILL considers to be end stations on a link and
that support an RBridge Channel protocol using this transport,
the destination MAC address is the TRILL-End-Stations multicast
address (see Section 7). A native RBridge Channel frame received
at an end station is discarded if its destination MAC address is
neither the unicast address of the port nor the multicast address
TRILL-End-Stations.

Eastlake, et al. Standards Track [Page 14]

RFC 7178 TRILL: RBridge Channel Support May 2014

3. The RBridge-Channel outer Ethertype must be present. In the
future, there may be other protocols using the All-Edge-RBridges
and/or TRILL-End-Stations multicast addresses on native frames
distinguished by different Ethertypes.

4. The NA or Native bit in the RBridge Channel Header flags MUST be
a one.

5. There might be additional tags present between the Outer.MacDA,
Outer.MacSA pair, and the RBridge-Channel Ethertype.

The RBridge Channel protocol number space for native RBridge Channel
messages and TRILL Data formatted RBridge Channel messages is the
same. If provided for by the channel protocol involved, the receipt
of a native RBridge Channel frame MAY lead to the generation and
transmission of one or more Inter-RBridge Channel frames. The
decapsulation and processing of a TRILL Data RBridge Channel frame
MAY, if provided for by the channel protocol involved, result in the
sending of one or more native RBridge Channel frames to one or more
end stations. Thus, there could be an RBridge Channel protocol that
involved an RBridge Channel message sent (1) from an origin RBridge
where the message is created, (2) through one or more transit
RBridges, and (3) from a final RBridge as a native RBridge Channel
message to an end station (or the reverse of such a three-part path);
however, to do this, the RBridge Channel protocol involved must be
implemented at the RBridge where the channel message is changed
between a native frame and a TRILL Data format frame, and that
RBridge must change the channel message itself, at a minimum
complementing the NA flag in the Channel Header and making
appropriate MAC address changes.

An erroneous native channel message results in a native RBridge
Channel Error message under the same conditions for which a TRILL
Data RBridge Channel message would result in a TRILL Data RBridge
Channel Error message. However, in a native RBridge Channel Error
message, the NA flag MUST be one. Also, since there is no TRILL
Header in native RBridge Channel protocol frames, the beginning part
of the frame in which the error was detected that is included in
native RBridge Channel Error frames starts with the RBridge Channel
Header (including the RBridge-Channel Ethertype). The destination
MAC address of such error messages is set to the source MAC address
of the native RBridge Channel message that was in error.

There is no mechanism to stop end stations from directly exchanging
native RBridge Channel messages, but such usage is beyond the scope
of this document.

Eastlake, et al. Standards Track [Page 15]

RFC 7178 TRILL: RBridge Channel Support May 2014

5. Indicating Support for RBridge Channel Protocols

Support for RBridge Channel protocols is indicated by the presence of
one or more TLVs and/or sub-TLVs in an RBridge's Link State PDU (LSP)
as documented in [RFC7176].

RBridge Channel protocols 0 and 0xFFF are reserved, and protocol 1,
the RBridge Channel Error protocol, MUST be implemented as part of
the RBridge Channel feature. Thus, if an RBridge supports the
RBridge Channel feature, it should be advertising support for
protocol 1 and not advertising support for protocols 0 or 0xFFF in
its LSP. However, indication of support or non-support for RBridge
Channel protocol 1 is ignored on receipt, and support for it is
always assumed if support for any RBridge Channel is indicated in the
RBridge's LSP.

6. Congestion Considerations

The bandwidth resources used by RBridge Channel protocols are
recommended to be small compared to the total bandwidth of the links
they traverse. When doing network planning, the bandwidth
requirements for TRILL Data, TRILL IS-IS, TRILL ESADI, RBridge
Channel protocol traffic, and any other link-local traffic need to be
taken into account.

Specifications for particular RBridge Channel protocols MUST consider
congestion and bandwidth usage implications and provide guidance on
bandwidth or packet-frequency management. RBridge Channel protocols
can have built-in bandwidth management in their protocols. Outgoing
channel messages SHOULD be rate-limited, by configuring the
underlying protocols or otherwise, to prevent aggressive connectivity
verification or other applications consuming excessive bandwidth,
causing congestion, or becoming denial-of-service attacks.

If these conditions cannot be followed, an adaptive loss-based scheme
SHOULD be applied to congestion-control outgoing RBridge Channel
traffic, so that it competes fairly, taking into account packet
priorities and drop eligibility as indicated in the Inner.VLAN, with
TCP or similar traffic within an order of magnitude. One method of
determining an acceptable bandwidth for RBridge Channel traffic is
described in [RFC5348]; other methods exist. For example, bandwidth
or packet-frequency management can include any of the following: a
negotiation of transmission interval/rate such as that provided in
BFD [RFC5880], a throttled transmission rate on "congestion detected"
situations, a gradual ramp-up after shutdown due to congestion and
until basic connectivity is verified, and other mechanisms.

Eastlake, et al. Standards Track [Page 16]

RFC 7178 TRILL: RBridge Channel Support May 2014

Connectivity-checking applications such as BFD [RFC5880] SHOULD be
rate-limited to below 5% of the bitrate of the associated link or
links. For this purpose, the mean or sustained bitrate of the link
or links is used.

Incoming RBridge Channel messages MAY be rate-limited as a protection
against denial-of-service attacks. This throttling of incoming
messages SHOULD honor packet priorities and drop eligibility
indications as indicated in the Inner.VLAN, preferentially discarding
drop-eligible and lower-priority packets.

7. Allocation Considerations

The following subsections give IANA and IEEE allocation
considerations. In this document, the allocation procedure
specifications are as defined in [RFC5226].

7.1. IANA Considerations

IANA has allocated a previously unassigned TRILL Nickname as follows:

Any-RBridge 0xFFC0

IANA has added "All-Egress-RBridges" to the TRILL Parameter Registry
as an alternative name for the "All-ESADI-RBridges" multicast
address.

IANA has allocated two previously unassigned TRILL multicast
addresses as follows:

TRILL-End-Stations 01-80-C2-00-00-45
All-Edge-RBridges 01-80-C2-00-00-46

IANA has created an additional sub-registry in the TRILL Parameter
Registry for RBridge Channel Protocols, with initial contents as
follows:

Protocol Description Reference
-------- ----------- ---------

0x000 Reserved; not to be allocated (This document)
0x001 RBridge Channel Error (This document)
0x002-0x0FF Unassigned (1)
0x100-0xFF7 Unassigned (2)
0xFF8-0xFFE Reserved for Private Use
0xFFF Reserved; not to be allocated (This document)

Eastlake, et al. Standards Track [Page 17]

RFC 7178 TRILL: RBridge Channel Support May 2014

(1) RBridge Channel protocol code points from 0x002 to 0x0FF require
a Standards Action, as modified by [RFC7120], for allocation.

(2) RBridge Channel protocol code points from 0x100 to 0xFF7 are RFC
Required to allocate a single value or IESG Approval to allocate
multiple values.

IANA has created an additional sub-registry in the TRILL Parameter
Registry for RBridge Channel Header Flags with initial contents as
follows:

Flag Bit Mnemonic Allocation
-------- -------- ----------

0 SL Silent
1 MH Multi-hop
2 NA Native
3-11 - Unassigned

Allocation of an RBridge Channel Header Flag is based on IETF Review.

IANA has created an additional sub-registry in the TRILL Parameter
Registry for RBridge Channel Error Codes with initial contents as
listed in Section 3.2 above and with available values allocated by
Standards Action as modified by [RFC7120].

7.2. IEEE Registration Authority Considerations

The IEEE Registration Authority has assigned the Ethertype 0x8946 for
TRILL RBridge Channel.

8. Security Considerations

No general integrity, authentication, or encryption mechanisms are
provided herein for RBridge Channel messages. If these services are
required for a particular RBridge Channel protocol, they MUST be
supplied by that channel protocol. See, for example, the BFD
Authentication mechanism [RFC5880].

See [RFC6325] for general TRILL security considerations. As stated
therein, no protection is provided by TRILL against forging of the
Ingress Nickname in a TRILL Data formatted channel message or the
Outer.MacSA in a native RBridge Channel frame on an Ethernet link.
This may result in misdirected return responses or error messages.
However, link-level security protocols may be used to authenticate
the origin station on a link and protect against attacks on links.
See also Section 6 concerning congestion.

Eastlake, et al. Standards Track [Page 18]

RFC 7178 TRILL: RBridge Channel Support May 2014

If indications of RBridge Channel Protocol support are improperly
absent from an RBridge's LSP, it could deny all RBridge Channel
services, for example, some BFD services, for the RBridge in
question. If a particular RBridge Channel protocol is incorrectly
not advertised as supported, it could deny the service of that
channel protocol to the RBridge in question.

Incorrect indication of RBridge Channel Protocol support or incorrect
assertion of support for a channel protocol could encourage RBridge
Channel messages to be sent to an RBridge that does not support the
channel feature or the particular channel protocol used. The inner
frame of such messages could be decapsulated and that inner frame
could be sent out all ports that are Appointed Forwarders for the
frame's Inner.VLAN. However, this is unlikely to cause much harm; in
particular, there are two possibilities as follows: (a) if end
stations do not recognize the RBridge-Channel Ethertype of the frame,
they will drop it, and (b) if end stations do recognize the RBridge-
Channel Ethertype and the channel protocol indicated in the frame,
they should refuse to process the frame due to an incorrect value of
the RBridge Channel Header NA flag.

9. References

9.1. Normative References

[IS-IS] International Organization for Standardization,
"Intermediate System to Intermediate System intra-domain
routeing information exchange protocol for use in
conjunction with the protocol for providing the
connectionless-mode network service (ISO 8473)", Second
Edition, November 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.

[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.

[RFC5348] Floyd, S., Handley, M., Padhye, J., and J. Widmer, "TCP
Friendly Rate Control (TFRC): Protocol Specification", RFC
5348, September 2008.

Eastlake, et al. Standards Track [Page 19]

RFC 7178 TRILL: RBridge Channel Support May 2014

[RFC6325] Perlman, R., Eastlake 3rd, D., Dutt, D., Gai, S., and A.
Ghanwani, "Routing Bridges (RBridges): Base Protocol
Specification", RFC 6325, July 2011.

[RFC7120] Cotton, M., "Early IANA Allocation of Standards Track Code
Points", BCP 100, RFC 7120, January 2014.

[RFC7176] Eastlake 3rd, D., Senevirathne, T., Ghanwani, A., Dutt,
D., and A. Banerjee, "Transparent Interconnection of Lots
of Links (TRILL) Use of IS-IS", RFC 7176, May 2014.

[RFC7177] Eastlake 3rd, D., Perlman, R., Ghanwani, A., Yang, H., and
V. Manral, "Transparent Interconnection of Lots of Links
(TRILL): Adjacency", RFC 7177, May 2014.

[RFC7179] Eastlake 3rd, D., Ghanwani, A., Manral, V., Li, Y., and C.
Bestler, "Transparent Interconnection of Lots of Links
(TRILL): Header Extension", RFC 7179, May 2014.

9.2. Informative References

[RFC5082] Gill, V., Heasley, J., Meyer, D., Savola, P., Ed., and C.
Pignataro, "The Generalized TTL Security Mechanism
(GTSM)", RFC 5082, October 2007.

[RFC5586] Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed.,
"MPLS Generic Associated Channel", RFC 5586, June 2009.

[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, June 2010.

[RFC5882] Katz, D. and D. Ward, "Generic Application of
Bidirectional Forwarding Detection (BFD)", RFC 5882, June
2010.

[RFC7180] Eastlake 3rd, D., Zhang, M., Ghanwani, A., Manral, V., and
A. Banerjee, "Transparent Interconnection of Lots of Links
(TRILL): Clarifications, Corrections, and Updates", RFC
7180, May 2014.

10. Acknowledgments

The authors gratefully acknowledge the comments and contributions of
the follows, listed is alphabetic order: Stewart Bryant, Somnath
Chatterjee, Adrian Farrel, Stephen Farrell, Miguel A. Garcia, Anoop
Ghanwani, Brian Haberman, Rakesh Kumar, Barry Leiba, and Tissa
Senevirathne.

Eastlake, et al. Standards Track [Page 20]

RFC 7178 TRILL: RBridge Channel Support May 2014

Authors' Addresses

Donald Eastlake 3rd
Huawei R&D USA
155 Beaver Street
Milford, MA 01757
USA
Phone: +1-508-333-2270
EMail: [email protected]

Vishwas Manral
Ionos Corp.
4100 Moorpark Ave.
San Jose, CA 95117
USA
EMail: [email protected]

Yizhou Li
Huawei Technologies
101 Software Avenue,
Nanjing 210012
China
Phone: +86-25-56622310
EMail: [email protected]

Sam Aldrin
Huawei Technologies
2330 Central Expressway
Santa Clara, CA 95050
USA
Phone: +1-408-330-5000
EMail: [email protected]

Dave Ward
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
USA

EMail: [email protected]

Eastlake, et al. Standards Track [Page 21]