TRILL Working Group Donald Eastlake
Intended status: Proposed Standard Vishwas Manral
Expires: January 12, 2013 July 13, 2012
TRILL: RBridge Channel Support
This document specifies a general channel mechanism for sending
messages, such as BFD (Bidirectional Forwarding Detection) messages,
between RBridges (Routing Bridges) and between RBridges and end
stations in an RBridge campus through extensions to the TRILL
(TRansparent Interconnection of Lots of Links) protocol.
Status of This Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
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D. Eastlake, et al [Page 1]INTERNET-DRAFT TRILL: RBridge ChannelTable of Contents
1.1 RBridge Channel Requirements...........................3
1.2 Relation to the MPLS Generic Channel...................4
2. Inter-RBridge Channel Messages..........................5
2.1 The RBridge Channel Message Inner Frame................6
2.1.1 RBridge Channel Header...............................6
2.1.1 Inner Ethernet Header................................8
2.1.3 Inner.VLAN Tag.......................................8
2.2 The TRILL Header for RBridge Channel Messages..........9
2.3 Ethernet Link Header and Trailer......................10
2.4 Special Transmission and Rate Considerations..........11
3. Processing RBridge Channel TRILL Data Messages.........12
3.1 Processing the RBridge Channel Header.................12
3.2 RBridge Channel Errors................................13
4. Native RBridge Channel Frames..........................15
5. Indicating Support for RBridge Channel Protocols.......17
6. Congestion Considerations..............................18
7. Allocation Considerations..............................19
7.1 IANA Considerations...................................19
7.2 IEEE Registration Authority Considerations............20
8. Security Considerations................................21
9.1 Normative References..................................22
9.2 Informative References................................23
Appendix: Change History..................................24
D. Eastlake, et al [Page 2]INTERNET-DRAFT TRILL: RBridge Channel1. Introduction
RBridge campuses provide transparent least-cost forwarding using the
TRILL (TRansparent Interconnection of Lots of Links) protocol that
builds on IS-IS (Intermediate System to Intermediate System) routing
[IS-IS] [RFC1195] [RFC6326bis]. Devices that implement TRILL are
called RBridges (Routing Bridges) 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
(Bidirectional Forwarding Detection, [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 [RFCext] 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 TRILL Data encapsulated for inter-RBridge channel
D. Eastlake, et al [Page 3]INTERNET-DRAFT TRILL: RBridge Channel
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 Channel
The RBridge Channel is similar to the MPLS Generic 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).
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
D. Eastlake, et al [Page 4]INTERNET-DRAFT TRILL: RBridge Channel2. 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.
The diagram below shows the overall structure of a 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 a RBridge Channel Alert extended TRILL header flag as
further described in Section 3 below.
The Sections 2.1 and 2.2 below describe the Inner frame and the TRILL
Header for frames sent in an RBridge Channel. As always, the Outer
link header and 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
D. Eastlake, et al [Page 5]INTERNET-DRAFT TRILL: RBridge Channel
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
2.1 The 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 |
RBridge Channel Protocol Specific Information:
+ 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 below.
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:
D. Eastlake, et al [Page 6]INTERNET-DRAFT TRILL: RBridge Channel
CHV: A 4-bit field that gives the RBridge Channel Header Version.
This document specifies version zero.
Channel Protocol: A 12-bit unsigned integer that specifies the
particular RBridge Channel protocol to which the message
Flags: Provides 12 bits of flags described below.
ERR: A 4-bit unsigned integer used in connection with error
reporting at the RBridge Channel level as described in
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, which is the high order bit in network order, is defined as
the SL or Silent bit. If it is a one, it suppresses RBridge
Channel Error messages (see Section 3).
Bit 1 is 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 is 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
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
D. Eastlake, et al [Page 7]INTERNET-DRAFT TRILL: RBridge Channel
avoid conflicting use of these code points and unacceptable burdens
within the private network from their use.
2.1.1 Inner Ethernet Header
The special Inner.MacDA is the All-Egress-RBridges multicast 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
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
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
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:
D. Eastlake, et al [Page 8]INTERNET-DRAFT TRILL: RBridge Channel
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.
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,
[ClearCorrect]). 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 The 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
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
D. Eastlake, et al [Page 9]INTERNET-DRAFT TRILL: RBridge Channel
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 Hops field to the maximum value and checking the Hop Count field
on receipt provides an additional validity check as discussed in
The RBridge originating a channel message places a nickname that it
holds into 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 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
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
2.3 Ethernet Link Header and Trailer
An RBridge Channel frame has the usual link header and 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.
D. Eastlake, et al [Page 10]INTERNET-DRAFT TRILL: RBridge Channel2.4 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
included in the routing topology because it was in the Report state
as specified in [RFC6327].
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 Two-Way states, as specified in [RFC6327], 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,
D. Eastlake, et al [Page 11]INTERNET-DRAFT TRILL: RBridge Channel3. 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 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.
RBridge Channel messages SHOULD only be sent to RBridges that
advertise support for the channel protocol involved as described in
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
critical RBridge Channel Alert flag is set [RFCext]. However, if
these conditions are detected at a transit RBridge examining the
message because the non-critical RBridge Channel Alert flag is set
D. Eastlake, et al [Page 12]INTERNET-DRAFT TRILL: RBridge Channel
[RFCext] but the critical RBridge Channel Alert flag is not set, no
error is generated and the frame is still forwarded normally.
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
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
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
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 non-
critical RBridge Channel Alert bit 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
D. Eastlake, et al [Page 13]INTERNET-DRAFT TRILL: RBridge Channel
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
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 - Available for allocation, see Section 7.
15 Reserved (see Note)
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 a RBridge
Channel Error message, that is, a channel message with a protocol
value of 0x001 or with a non-zero ERR field.
D. Eastlake, et al [Page 14]INTERNET-DRAFT TRILL: RBridge Channel4. 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
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 that uses 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 with a destination MAC address that is a unicast
address different from that of the port or multicast address
different from All-Edge-RBridges, is discarded. If the frame is
multicast by an RBridge to all the devices that TRILL considers
to be end stations on a link that support an RBridge Channel
protocol that uses 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 with a
destination MAC address that is a unicast address different
from that of the port or multicast address different from
TRILL-End-Stations, is discarded.
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.
D. Eastlake, et al [Page 15]INTERNET-DRAFT TRILL: RBridge Channel
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 from an origin RBridge where
the message is created, through one or more transit RBridges and from
the last as a native RBridge channel message to and end station or
the reverse of such a 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 an 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
D. Eastlake, et al [Page 16]INTERNET-DRAFT TRILL: RBridge Channel5. 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 LSP as documented in
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
D. Eastlake, et al [Page 17]INTERNET-DRAFT TRILL: RBridge Channel6. 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, the TRILL ESADI protocol,
RBridge Channel 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.
Connectivity chcking applications such as BFD [RFC5880] SHOULD be
rate-limited to below 5% of the bit-rate of the associated link or
links. For this purpose, the mean or sustained bit-rate 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 indicate in the Inner.VLAN, preferentially discarding
drop eligible and lower priority packets.
D. Eastlake, et al [Page 18]INTERNET-DRAFT TRILL: RBridge Channel7. 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 is requested to allocate a previously unassigned TRILL Nickname
Any-RBridge TBD (0xFFCO suggested)
IANA is requested to add "All-Egress-RBridges" to the TRILL Parameter
Registry as an alternative name for the "All-ESADI-RBridges"
IANA is requested to allocate two previously unassigned TRILL
Multicast address as follows:
TRILL-End-Stations TBD (01-80-C2-00-00-45 suggested)
All-Edge-RBridges TBD (01-80-C2-00-00-46 suggested)
IANA is requested to create 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 Available (1)
0x100-0xFF7 Available (2)
0xFF8-0xFFE Private Use
0xFFF Reserved, not to be allocated (This document)
(1) RBridge Channel protocol code points from 0x002 to 0x0FF require
a Standards Action, as modified by [RFC4020], 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
IANA is requested to create an additional sub-registry in the TRILL
Parameter Registry for RBridge Channel Header Flags with initial
contents as follows:
D. Eastlake, et al [Page 19]INTERNET-DRAFT TRILL: RBridge Channel
Flag Bit Mnemonic Allocation
-------- -------- ----------
0 SL Silent
1 MH Multi-hop
2 NA Native
3-11 - Available for allocation
Allocation of an RBridge Channel Header Flag is based on IETF Review.
IANA is requested to create 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 [RFC4020].
7.2 IEEE Registration Authority Considerations
The IEEE Registration Authority has assigned the Ethertype <TBD> for
D. Eastlake, et al [Page 20]INTERNET-DRAFT TRILL: RBridge Channel8. 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 above concerning congestion.
If indication 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. (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.
D. Eastlake, et al [Page 21]INTERNET-DRAFT TRILL: RBridge Channel9. References
The following sections list normative and informative references for
9.1 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.
[RFC4020] - Kompella, K. and A. Zinin, "Early IANA Allocation of
Standards Track Code Points", BCP 100, RFC 4020, February 2005.
[RFC5226] - Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226, May
[RFC5348] - Floyd, S., Handley, M., Padhye, J., and J. Widmer, "TCP
Friendly Rate Control (TFRC): Protocol Specification", RFC
5348, September 2008.
[RFC6325] - Perlman, R., Eastlake 3rd, D., Dutt, D., Gai, S., and A.
Ghanwani, "Routing Bridges (RBridges): Base Protocol
Specification", RFC 6325, July 2011.
[RFC6327] - Eastlake 3rd, D., Perlman, R., Ghanwani, A., Dutt, D.,
and V. Manral, "Routing Bridges (RBridges): Adjacency", RFC
6327, July 2011.
[RFCext] - D. Eastlake, A. Ghanwani, V. Manral, Y. Li, C. Bestler,
"TRILL: TRILL Header Extension", draft-ietf-trill-rbridge-
extension, in RFC Editor's queue.
[RFC6326bis] - Eastlake, D., A. Banerjee, D. Dutt, A. Ghanwani, R.
Perlman, "TRILL Use of IS-IS", draft-eastlake-isis-rfc6326bis,
work in progress.
D. Eastlake, et al [Page 22]INTERNET-DRAFT TRILL: RBridge Channel9.2 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] - D. Katz, D. Ward, "Bidirectional Forwarding Detection
(BFD)", June 2010.
[RFC5882] - D. Katz, D. Ward, "Generic Application of Bidirectional
Forwarding Detection (BFD)", June 2010.
[ClearCorrect] - D. Eastlake, M. Zhang, A. Ghanwani, A. Banerjee, V.
Manral, "TRILL: Clarifications, Corrections, and Updates",
draft-ietf-trill-clear-correct, work in progress.
D. Eastlake, et al [Page 23]INTERNET-DRAFT TRILL: RBridge ChannelAppendix: Change History
RFC Editor: please delete this appendix before publication.
Changes from -00 to -01
1. Spell out more acronyms.
2. Add reference to "Guidelines for the Use of OAM" draft.
3. Move definition of Alert flag to draft-ietf-trill-rbridge-options
and refer to it as an extended header flag.
4. Change name of "Egress-RBridges" multicast address to "All-Egress-
RBridges". Merge with All-ESADI-RBridges (i.e., they are two names
for the same MAC address).
5. Add detailed bit vector description for indicating support of
RBridge channel protocols. Add GENAPP and an APPsub-TLV to hold
one or more bit vectors.
6. Assorted editorial changes.
Changes from -01 to -02
1. Update for drafts that have been issued as RFCs.
2. Change to specification of Inner.VLAN in RBridge channel messages.
3. Remove GENAPP and move RBridge Channels supported information to
4. Clarify native RBridge Channel error messages.
5. Assorted editorial changes.
Changes from -02 to -03
1. Liberalize restrictions on RBridge acceptance of native RBridge
Channel messages. These are typically messages and should
generally be accepted unless in a VLAN not enabled at the port or
2. Change multi-cast address used by end stations in sending a native
D. Eastlake, et al [Page 24]INTERNET-DRAFT TRILL: RBridge Channel
RBridge Channel message to all RBridges on the link from All-
Egress-RBridges to All-Edge-RBridges to avoid possible confusion
if such a frame were encapsulated resulting in an All-Egress-
3. Reword references to "two-hop echo" and the like for clarity.
(This meant an echo frame that went to an immediate neighbor and
4. Add reference to and move some material to the RFC 6326bis draft.
5. Assorted editorial changes.
Changes from -03 to -04
1. Update for the replacement of the CFI bit by the DEI bit (see
2. Update for the existence of both critical and non-critical RBridge
Channel alert flags.
3. Update author information.
4. Assorted editorial changes.
Changes from -04 to -05
1. Clarify the distinction between native and non-native RBridge
Channel messages and that native channel messages are only
intended to be transmitted between RBridge and end stations on the
2. Add a paragraph to the Security Considerations section about
forged ingress nicknames / source MAC addresses in channel
3. Add acknowledgements section.
4. Replace "OAM" references with "BFD" references in Abstract and
5. Very minor editorial changes.
D. Eastlake, et al [Page 25]INTERNET-DRAFT TRILL: RBridge Channel
Changes from -05 to -06
1. Improve wording in 2.1.1 re CHV values.
2. Revert "Ext-Len" to "Op-Len".
3. Fix typos and make minor editorial changes.
Changes from -06 to -07
1. Add bit numbers at top of figures where they were missing.
2. Add figure numbers and captions.
3. Add text to Section 2.1.1 concerning Private Use RBridge Channel
4. Change IANA Considerations for the allocation of multiple RBridge
Channel protocol numbers in the 0x100 to 0xFF7 range from IETF
Review to IESG Approval.
5. Add text that the intended use for ERR code 15 is for some future
error code expansion feature should more error codes be required
and indicate that protocol numbers 0x000 and 0xFFF are not to be
6. Captialize the first occurrence of "must" in Section 7.
7. Add statement that directly connected end-stations are not blocked
from communicating with each other using channel messages but such
messages are beyond the scope of this document.
8. Re-order and add some references to the Securty Considertions
9. Typo fixes and various editorial changes.
Changes from -07 to -08
1. Add congestion considerations section.
2. Minor editorial changes.
D. Eastlake, et al [Page 26]INTERNET-DRAFT TRILL: RBridge ChannelAcknowledgments
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
This document was prepared with raw nroff. All macros used were
defined in the document source files.
Donald Eastlake 3rd
Huawei R&D USA
155 Beaver Street
Milford, MA 01757 USA
19111 Pruneridge Avenue
Cupertino, CA 95014 USA
101 Software Avenue,
Nanjing 210012, China
2330 Central Expressway
Santa Clara, CA 95050 USA
D. Eastlake, et al [Page 27]INTERNET-DRAFT TRILL: RBridge Channel
170 W. Tasman Drive
San Jose, CA 95134 USA
D. Eastlake, et al [Page 28]INTERNET-DRAFT TRILL: RBridge ChannelCopyright, Disclaimer, and Additional IPR Provisions
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D. Eastlake, et al [Page 29]