rfc7978
Internet Engineering Task Force (IETF) D. Eastlake 3rd
Request for Comments: 7978 Huawei
Updates: 7178 M. Umair
Category: Standards Track IPinfusion
ISSN: 2070-1721 Y. Li
Huawei
September 2016
Transparent Interconnection of Lots of Links (TRILL):
RBridge Channel Header Extension
Abstract
The IETF TRILL (Transparent Interconnection of Lots of Links)
protocol includes an optional mechanism (specified in RFC 7178)
called RBridge Channel for the transmission of typed messages between
TRILL switches in the same campus and the transmission of such
messages between TRILL switches and end stations on the same link.
This document specifies extensions to the RBridge Channel protocol
header to support two features as follows: (1) a standard method to
tunnel payloads whose type can be indicated by Ethertype through
encapsulation in RBridge Channel messages; and (2) a method to
support security facilities for RBridge Channel messages. This
document updates RFC 7178.
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 7841.
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/rfc7978.
Eastlake, et al. Standards Track [Page 1]
RFC 7978 TRILL: RBridge Channel Extension September 2016
Copyright Notice
Copyright (c) 2016 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.
Eastlake, et al. Standards Track [Page 2]
RFC 7978 TRILL: RBridge Channel Extension September 2016
Table of Contents
1. Introduction ....................................................4
1.1. Terminology and Acronyms ...................................4
2. RBridge Channel Header Extension Format .........................5
3. Extended RBridge Channel Payload Types ..........................8
3.1. Null Payload ...............................................8
3.2. Ethertyped Payload .........................................9
3.2.1. RBridge Channel Message as the Payload ..............9
3.2.2. TRILL Data Packet as the Payload ...................10
3.2.3. TRILL IS-IS Packet as the Payload ..................10
3.3. Ethernet Frame ............................................11
4. Extended RBridge Channel Security ..............................13
4.1. Derived Keying Material ...................................14
4.2. SType None ................................................14
4.3. IS-IS CRYPTO_AUTH-Based Authentication ....................15
4.4. DTLS Pairwise Security ....................................17
4.5. Composite Security ........................................18
5. Extended RBridge Channel Errors ................................18
5.1. SubERRs ...................................................19
5.2. Secure Nested RBridge Channel Errors ......................19
6. IANA Considerations ............................................19
6.1. Extended RBridge Channel Protocol Number ..................19
6.2. RBridge Channel Protocol Subregistries ....................20
6.2.1. RBridge Channel Error Codes ........................20
6.2.2. RBridge Channel SubError Codes .....................20
6.2.3. Extended RBridge Channel Payload Types
Subregistry ........................................20
6.2.4. Extended RBridge Channel Security Types
Subregistry ........................................21
7. Security Considerations ........................................21
8. Normative References ...........................................22
9. Informative References .........................................23
Acknowledgements ..................................................25
Authors' Addresses ................................................25
Eastlake, et al. Standards Track [Page 3]
RFC 7978 TRILL: RBridge Channel Extension September 2016
1. Introduction
The IETF TRILL base protocol [RFC6325] [RFC7780] has been extended
with the RBridge Channel [RFC7178] facility to support transmission
of typed messages (for example, Bidirectional Forwarding Detection
(BFD) [RFC7175]) between two TRILL switches (RBridges) in the same
campus and the transmission of such messages between RBridges and end
stations on the same link. When sent between RBridges in the same
campus, a TRILL Data packet with a TRILL Header is used, and the
destination RBridge is indicated by nickname. When sent between a
RBridge and an end station on the same link in either direction, a
native RBridge Channel message [RFC7178] is used with no TRILL
Header, and the destination port or ports are indicated by a Media
Access Control (MAC) address. (There is no mechanism to stop end
stations on the same link from sending native RBridge Channel
messages to each other; however, such use is outside the scope of
this document.)
This document updates [RFC7178] and specifies extensions to the
RBridge Channel header that provide two additional facilities as
follows:
(1) A standard method to tunnel payloads, whose type may be
indicated by Ethertype, through encapsulation in RBridge
Channel messages.
(2) A method to provide security facilities for RBridge Channel
messages. Example uses requiring such facilities are the
security of Pull Directory messages [RFC7067], address flush
messages [AddrFlush], and port shutdown messages [TRILL-AF].
Use of each of these facilities is optional, except that, as
specified below, if this header extension is implemented, there are
two payload types that MUST be implemented. Both of the above
facilities can be used in the same packet. In case of conflict
between this document and [RFC7178], this document takes precedence.
1.1. Terminology and Acronyms
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[RFC2119].
This document uses terminology and abbreviations defined in [RFC6325]
and [RFC7178]. Some of these are listed below for convenience along
with new terms and abbreviations.
Eastlake, et al. Standards Track [Page 4]
RFC 7978 TRILL: RBridge Channel Extension September 2016
application_data - A DTLS [RFC6347] message type.
Data Label - VLAN or FGL.
DTLS - Datagram Transport Layer Security [RFC6347].
FCS - Frame Check Sequence.
FGL - Fine-Grained Label [RFC7172].
HKDF - HMAC-based Key Derivation Function [RFC5869].
IS-IS - Intermediate System to Intermediate System [IS-IS].
PDU - Protocol Data Unit.
MTU - Maximum Transmission Unit.
RBridge - An alternative term for a TRILL switch.
SHA - Secure Hash Algorithm [RFC6234].
Sz - Campus-wide minimum link MTU [RFC6325] [RFC7780].
TRILL - Transparent Interconnection of Lots of Links or Tunneled
Routing in the Link Layer.
TRILL switch - A device that implements the TRILL protocol
[RFC6325] [RFC7780], sometimes referred to as an RBridge.
2. RBridge Channel Header Extension Format
The general structure of an RBridge Channel message between two TRILL
switches (RBridges) in the same campus is shown in Figure 1 below.
The structure of a native RBridge Channel message sent between an
RBridge and an end station on the same link, in either direction, is
shown in Figure 2 and, compared with the first case, omits the TRILL
Header, inner Ethernet addresses, and Data Label. A Protocol field
in the RBridge Channel Header gives the type of RBridge Channel
message and indicates how to interpret the Channel-Protocol-Specific
Payload [RFC7178].
Eastlake, et al. Standards Track [Page 5]
RFC 7978 TRILL: RBridge Channel Extension September 2016
+-----------------------------------+
| Link Header |
+-----------------------------------+
| TRILL Header |
+-----------------------------------+
| Inner Ethernet Addresses |
+-----------------------------------+
| Data Label (VLAN or FGL) |
+-----------------------------------+
| RBridge Channel Header |
+-----------------------------------+
| Channel-Protocol-Specific Payload |
+-----------------------------------+
| Link Trailer (FCS if Ethernet) |
+-----------------------------------+
Figure 1: RBridge Channel Packet Structure
+-----------------------------------+
| Ethernet Link Header |
+-----------------------------------+
| RBridge Channel Header |
+-----------------------------------+
| Channel-Protocol-Specific Payload |
+-----------------------------------+
| FCS |
+-----------------------------------+
Figure 2: Native RBridge Channel Frame
The RBridge Channel Header looks like this:
1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x8946 | CHV=0 | Channel Protocol |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | ERR | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ /
/ Channel-Protocol-Specific Data /
/-+-+-+-+-+- /
Figure 3: RBridge Channel Header
where 0x8946 is the RBridge-Channel Ethertype and CHV is the Channel
Header Version. This document is based on RBridge Channel version
zero.
Eastlake, et al. Standards Track [Page 6]
RFC 7978 TRILL: RBridge Channel Extension September 2016
The header extensions specified herein are in the form of an RBridge
Channel protocol, the Extended RBridge Channel Protocol. Figure 4
below expands the RBridge Channel Header and Protocol-Specific
Payload above for the case where the header extension is present.
1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 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
RBridge Channel Header:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x8946 | CHV=0 | Channel Protocol=0x004|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | ERR |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Header Extension Specific: | SubERR| RESV4 | SType | PType |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Security Information, variable length (0 length if SType = 0) /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
| Tunneled Data, variable length
| ...
Figure 4: RBridge Channel Header Extension Structure
The RBridge Channel Header Protocol field is used to indicate that
the header extension is present. Its contents MUST be the value
allocated for this purpose (see Section 6). The use of an RBridge
Channel protocol to indicate extensions makes it easy to determine if
a remote RBridge in the campus supports extensions since RBridges
advertise in their LSP which such protocols they support.
The Extended RBridge Channel-Protocol-Specific Data fields are as
follows:
SubERR: This field provides further details when an error is
indicated in the RBridge Channel ERR field. If ERR is zero,
then SubERR MUST be sent as zero and ignored on receipt. See
Section 5.
RESV4: This field MUST be sent as zero. If non-zero when
received, this is an error condition. See Section 5.
SType: This field describes the type of security information and
features, including keying material, being used or provided by
the extended RBridge Channel message. See Section 4.
PType: Payload Type. This describes the tunneled data. See
Section 3.
Eastlake, et al. Standards Track [Page 7]
RFC 7978 TRILL: RBridge Channel Extension September 2016
Security Information: Variable-length information. Length is zero
if SType is zero. See Section 4.
The RBridge Channel Header Extension is integrated with the RBridge
Channel facility. Extension errors are reported as if they were
RBridge Channel errors, using newly allocated code points in the ERR
field of the RBridge Channel Header supplemented by the SubERR field.
3. Extended RBridge Channel Payload Types
The Extended RBridge Channel Protocol can carry a variety of payloads
as indicated by the PType (Payload Type) field. Values are shown in
the table below with further explanation below the table (see also
Section 6.2.2).
PType Description Reference
----- ----------- ---------
0 Reserved
1 Null Section 3.1 of RFC 7978
2 Ethertyped Payload Section 3.2 of RFC 7978
3 Ethernet Frame Section 3.3 of RFC 7978
4-14 Unassigned
15 Reserved
Table 1: Payload Type Values
While implementation of the RBridge Channel Header Extension is
optional, if it is implemented, PType 1 (Null) MUST be implemented
and PType 2 (Ethertyped Payload) with the RBridge-Channel Ethertype
MUST be implemented. PType 2 for any Ethertypes other than the
RBridge-Channel Ethertype MAY be implemented. PType 3 MAY be
implemented.
The processing of any particular extended header RBridge Channel
message and its payload depends on meeting local security and other
policy at the destination TRILL switch or end station.
3.1. Null Payload
The Null payload type (PType = 1) is intended to be used for testing
or for messages such as key negotiation or the like where only
security information is present. It indicates that there is no user
data payload. Any tunneled user data after the Security Information
field is ignored. If the RBridge Channel Header Extension is
implemented, the Null Payload MUST be supported in the sense that an
"Unsupported PType" error is not returned (see Section 5). Any
particular use of the Null Payload should specify what VLAN or FGL
Eastlake, et al. Standards Track [Page 8]
RFC 7978 TRILL: RBridge Channel Extension September 2016
and what priority should be used in the inner Data Label of the
RBridge Channel message (or in an outer VLAN tag for the native
RBridge Channel message case) when those values are relevant.
3.2. Ethertyped Payload
A PType of 2 indicates that the payload (tunneled data) of the
extended RBridge Channel message begins with an Ethertype. A TRILL
switch supporting the RBridge Channel Header Extension MUST support a
PType of 2 with a payload beginning with the RBridge-Channel
Ethertype as described in Section 3.2.1. Other Ethertypes, including
the TRILL and L2-IS-IS Ethertypes as described in Sections 3.2.2 and
3.2.3, MAY be supported.
3.2.1. RBridge Channel Message as the Payload
A PType of 2 whose payload has an initial RBridge-Channel Ethertype
indicates an encapsulated RBridge Channel message. A typical reason
for sending an RBridge Channel message inside an extended RBridge
Channel message is to provide security services, such as
authentication or encryption, for the encapsulated message.
This RBridge Channel message type looks like the following:
1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RBridge-Channel (0x8946) | CHV=0 | Channel Protocol=0x004|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | ERR | SubERR| RESV4 | SType | 0x2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ Security Information, variable length (0 length if SType = 0) /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RBridge-Channel (0x8946) | CHV=0 |Nested Channel Protocol|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | ERR | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Nested Channel-Protocol-Specific Data ... /
/ /
Figure 5: Message Structure with RBridge Channel Payload
Eastlake, et al. Standards Track [Page 9]
RFC 7978 TRILL: RBridge Channel Extension September 2016
3.2.2. TRILL Data Packet as the Payload
A PType of 2 whose payload has an initial TRILL Ethertype indicates
an encapsulated TRILL Data packet as shown in Figure 6. If this
Ethertype is supported for PType = 2 and the message meets local
policy for acceptance, the TRILL Data packet is handled as if it had
been received by the destination TRILL switch on the port where the
Extended RBridge Channel message was received.
1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RBridge-Channel (0x8946) | CHV=0 | Channel Protocol=0x004|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | ERR | SubERR| RESV4 | SType | 0x2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ Security Information, variable length (0 length if SType = 0) /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TRILL (0x22F3) | V |A|C|M| RESV |F| Hop Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Egress Nickname | Ingress Nickname |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ Optional Flags Word /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Inner.MacDA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Inner.MacDA continued | Inner.MacSA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Inner.MacSA (cont.) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Inner Data Label (2 or 4 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
| TRILL Data Packet payload
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
Figure 6: Message Structure with TRILL Data Packet Payload
The optional flags word is only present if the F bit in the TRILL
Header is one [RFC7780].
3.2.3. TRILL IS-IS Packet as the Payload
A PType of 2 and an initial L2-IS-IS Ethertype indicate that the
payload of the Extended RBridge Channel protocol message is an
encapsulated TRILL IS-IS PDU as shown in Figure 7. If this Ethertype
is supported for PType = 2, the tunneled TRILL IS-IS packet is
processed by the destination RBridge if it meets local policy. One
possible use is to expedite the receipt of a link state PDU (LSP) by
Eastlake, et al. Standards Track [Page 10]
RFC 7978 TRILL: RBridge Channel Extension September 2016
some TRILL switch or switches with an immediate requirement for the
link state information. A link local IS-IS PDU would not normally be
sent via this Extended RBridge Channel method except possibly to
encrypt the PDU since such PDUs can just be transmitted on the link
and do not normally need RBridge Channel handling. (Link local IS-IS
PDUs are (1) Hello, CSNP, PSNP [IS-IS]; (2) MTU-probe, MTU-ack
[RFC7176]; and (3) circuit scoped FS-LSP, FS-CSNP, and FS-PSNP
[RFC7356].)
1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RBridge-Channel (0x8946) | CHV=0 | Channel Protocol=0x004|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | ERR | SubERR| RESV4 | SType | 0x2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ Security Information, variable length (0 length if SType = 0) /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
| L2-IS-IS (0x22F4) | 0x83 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| rest of IS-IS PDU
+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
Figure 7: Message Structure with TRILL IS-IS Packet Payload
3.3. Ethernet Frame
If PType is 3, the extended RBridge Channel payload is an Ethernet
frame as might be received from or sent to an end station except that
the encapsulated Ethernet frame's FCS is omitted, as shown in
Figure 8. (There is still an overall final FCS if the RBridge
Channel message is being sent on an Ethernet link.) If this PType is
implemented and the message meets local policy, the encapsulated
frame is handled as if it had been received on the port on which the
Extended RBridge Channel message was received.
The priority of the RBridge Channel message can be copied from the
Ethernet frame VLAN tag, if one is present, except that priority 7
SHOULD only be used for messages critical to establishing or
maintaining adjacency and priority 6 SHOULD only be used for other
important control messages.
Eastlake, et al. Standards Track [Page 11]
RFC 7978 TRILL: RBridge Channel Extension September 2016
1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RBridge-Channel (0x8946) | 0x0 | Channel Protocol=0x004|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | ERR | SubERR| RESV4 | SType | 0x3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ Security Information, variable length (0 length if SType = 0) /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MacDA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MacDA (cont.) | MacSA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MacSA (cont.) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Any Ethernet frame tagging...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
| Ethernet frame payload...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
Figure 8: Message Structure with Ethernet Frame Payload
In the case of a non-Ethernet link, such as a PPP (Point-to-Point
Protocol) link [RFC6361], the ports on the link are considered to
have link-local synthetic 48-bit MAC addresses constructed as
described below. Such a constructed address MAY be used as a MacSA.
If the RBridge Channel message is individually addressed to a link-
local port, the source TRILL switch will have the information to
construct such a MAC address for the destination TRILL switch port,
and that MAC address MAY be used as the MacDA. By the use of such a
MacSA and either such a unicast MacDA or a group-addressed MacDA, an
Ethernet frame can be sent between two TRILL switch ports connected
by a non-Ethernet link.
These synthetic TRILL switch port MAC addresses for non-Ethernet
ports are constructed as follows (and as shown in Figure 9): 0xFEFF,
the nickname of the TRILL switch used in TRILL Hellos sent on that
port, and the Port ID that the TRILL switch has assigned to that
port. (Both the Port ID of the port on which a TRILL Hello is sent
and the nickname of the sending TRILL switch appear in the Special
VLANs and Flags sub-TLV [RFC7176] in TRILL IS-IS Hellos.) The
resulting MAC address has the Local bit on and the Group bit off
[RFC7042]. However, since there will be no Ethernet end stations on
a non-Ethernet link in a TRILL campus, such synthetic MAC addresses
cannot conflict on the link with a real Ethernet port address
regardless of their values.
Eastlake, et al. Standards Track [Page 12]
RFC 7978 TRILL: RBridge Channel Extension September 2016
1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0xFEFF | Nickname |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Port ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: Synthetic MAC Address
4. Extended RBridge Channel Security
Table 2 below gives the assigned values of the SType (Security Type)
field and their meaning. Use of DTLS Pairwise Security (SType = 2)
or Composite Security (SType = 3) is RECOMMENDED.
While IS-IS CRYPTO_AUTH-based authentication is also specified and
can be used for both pairwise and multi-destination traffic, it
provides only authentication and is not considered to meet current
security standards. For example, it does not provide for key
negotiation; thus, its use is NOT RECOMMENDED.
The Extended RBridge Channel DTLS-based security specified in
Section 4.4 and the Composite Security specified in Section 4.5 are
intended for pairwise (known unicast) use. That is, the case where
the M bit in the TRILL Header is zero and any Outer.MacDA is
individually addressed.
Multi-destination Extended RBridge Channel packets would be those
with the M bit in the TRILL Header set to one or, in the native
RBridge Channel case, the Outer.MacDA would be group addressed. The
DTLS Pairwise Security and Composite Security STypes can also be used
in the multi-destination case by serially unicasting the messages to
all data-accessible RBridges (or stations in the native RBridge
Channel case) in the recipient group. For TRILL Data packets, that
group is specified by the Data Label; for native frames, the group is
specified by the groupcast destination MAC address. It is intended
to specify a true group keyed SType to secure multi-destination
packets in a separate document [GroupKey].
Eastlake, et al. Standards Track [Page 13]
RFC 7978 TRILL: RBridge Channel Extension September 2016
SType Description Reference
----- ----------- ---------
0 None Section 4.2 of RFC 7978
1 IS-IS CRYPTO_AUTH-Based Section 4.3 of RFC 7978
Authentication
2 DTLS Pairwise Security Section 4.4 of RFC 7978
3 Composite Security Section 4.5 of RFC 7978
4-14 Unassigned
15 Reserved
Table 2: SType Values
4.1. Derived Keying Material
In some cases, it is possible to use material derived from IS-IS
CRYPTO_AUTH keying material [RFC5310] as an element of Extended
RBridge Channel security. It is assumed that the IS-IS keying
material is of high quality. The material actually used is derived
from the IS-IS keying material as follows:
Derived Material =
HKDF-Expand-SHA256 ( IS-IS-key, "Extended Channel" | 0x0S, L )
where "|" indicates concatenation, HKDF is as in [RFC5869], SHA256 is
as in [RFC6234], IS-IS-key is the input IS-IS keying material,
"Extended Channel" is the 16-character ASCII [RFC20] string indicated
without any leading length byte or trailing zero byte, 0x0S is a
single byte where S is the SType for which this key derivation is
being used and the upper nibble is zero, and L is the length of the
output-derived material needed.
Whenever IS-IS keying material is being used as above, the underlying
IS-IS CRYPTO_AUTH keying material [RFC5310] might expire or be
invalidated. At the time of or before such expiration or
invalidation, the use of the Derived Material from the IS-IS keying
material MUST cease. Continued security MAY use new derived material
from currently valid IS-IS CRYPTO_AUTH keying material.
4.2. SType None
No security services are being invoked. The length of the Security
Information field (see Figure 4) is zero.
Eastlake, et al. Standards Track [Page 14]
RFC 7978 TRILL: RBridge Channel Extension September 2016
4.3. IS-IS CRYPTO_AUTH-Based Authentication
This SType provides security for Extended RBridge Channel messages
similar to that provided for [IS-IS] PDUs by the [IS-IS]
Authentication TLV. The Security Information (see Figure 4) is as
shown in Figure 10.
1 1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RESV | Size |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Key ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+
| Authentication Data (Variable)
+
|
+-+-+-+-+-+-+-+-+-+-+-+-+-...
Figure 10: SType 1 Security Information
o RESV: Four bits that MUST be sent as zero and ignored on receipt.
o Size: Set to 2 + the size of Authentication Data in bytes.
o Key ID: specifies the keying value and authentication algorithm
that the Key ID specifies for TRILL IS-IS LSP [RFC5310]
Authentication TLVs. The keying material actually used is always
derived as shown in Section 4.1.
o Authentication Data: The authentication data produced by the
derived key and algorithm associated with the Key ID acting on the
part of the TRILL Data packet shown. Length of the authentication
data depends on the algorithm. The authentication value is
included in the security information field and is treated as zero
when authentication is calculated.
As show in Figure 11, the area covered by this authentication starts
with the byte immediately after the TRILL Header optional Flag Word
if it is present. If the Flag Word is not present, it starts after
the TRILL Header Ingress Nickname. In either case, it extends to
just before the TRILL Data packet link trailer. For example, for an
Ethernet packet it would extend to just before the FCS.
Eastlake, et al. Standards Track [Page 15]
RFC 7978 TRILL: RBridge Channel Extension September 2016
+-----------------------------+
| Link Header |
+-----------------------------+
| TRILL Header |
| (plus optional Flag Word) |
+-----------------------------+ ^
| Inner Ethernet Addresses | |
+-----------------------------+ .
| Data Label (VLAN or FGL) | |
+-----------------------------+ .
| RBridge Channel Header | | <-authentication
+-----------------------------+ .
| Extended Channel Header | |
| (plus Security Information)| .
+-----------------------------+ |
| Payload | .
+-----------------------------+ v
| Link Trailer |
+-----------------------------+
Figure 11: SType 1 Authentication Coverage
In the native RBridge Channel case, this authentication coverage is
as specified in the above paragraph except that it starts with the
RBridge-Channel Ethertype, since there is no TRILL Header, inner
Ethernet addresses, or inner Data Label (see Figure 12).
+-----------------------------+
| Ethernet Header |
+-----------------------------+ ^
| RBridge Channel Header | |
+-----------------------------+ .
| Extended Channel Header | | <-authentication
| (plus Security Information)| .
+-----------------------------+ |
| Payload | .
+-----------------------------+ v
| Ethernet Trailer |
+-----------------------------+
Figure 12: Native SType 1 Authentication Coverage
RBridges, which are IS-IS routers, can reasonably be expected to hold
IS-IS CRYPTO_AUTH keying material [RFC5310] so that this SType can be
used for RBridge Channel messages, which go between RBridges. How
end stations might come to hold IS-IS CRYPTO_AUTH keying material is
Eastlake, et al. Standards Track [Page 16]
RFC 7978 TRILL: RBridge Channel Extension September 2016
beyond the scope of this document. Thus, this SType might not be
applicable to native RBridge Channel messages, which are between an
RBridge and an end station.
4.4. DTLS Pairwise Security
DTLS [RFC6347] supports key negotiation and provides both encryption
and authentication. The RBridge Channel Extended Header DTLS
Pairwise SType uses a negotiated DTLS version that MUST NOT be less
than 1.2.
When DTLS pairwise security is used, the entire payload of the
Extended RBridge Channel packet, starting just after the null
Security Information and ending just before the link trailer, is one
or more DTLS records [RFC6347]. As specified in [RFC6347], DTLS
records MUST be limited by the path MTU, in this case so that each
record fits entirely within a single Extended RBridge Channel
message. A minimum path MTU can be determined from the TRILL campus
minimum MTU Sz, which will not be less than 1470 bytes, by allowing
for the TRILL Data packet, extended RBridge Channel, and DTLS framing
overhead. With this SType, the security information between the
extended RBridge Channel header and the payload is null because all
the security information is in the payload area.
The DTLS Pairwise keying is set up between a pair of RBridges,
independent of Data Label, using messages of a priority configurable
at the RBridge level, which defaults to priority 6. DTLS message
types other than application_data can be the payload of an extended
RBridge Channel message with a TRILL Header using any Data Label,
and, for such DTLS message types, the PType in the RBridge Channel
Header Extension is ignored.
Actual application_data sent within such a message using this SType
SHOULD use the Data Label and priority as specified for that
application_data. In this case, the PType value in the RBridge
Channel Header Extension applies to the decrypted application_data.
TRILL switches that implement the extended RBridge Channel DTLS
Pairwise SType SHOULD support the use of certificates for DTLS, but
certificate size may be limited by the DTLS requirement that each
record fit within a single message. Appropriate certificate contents
are out of scope for this document.
TRILL switches that support the extended RBridge Channel DTLS
Pairwise SType MUST support the use of pre-shared keys. If the
psk_identity (see [RFC4279]) is two bytes, it is interpreted as a Key
ID as defined in [RFC5310], and the value derived as shown in
Section 4.1 from that key is used as a pre-shared key for DTLS
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RFC 7978 TRILL: RBridge Channel Extension September 2016
negotiation. A psk_identity with a length other than two bytes MAY
be used to indicate other implementation-dependent pre-shared keys.
Pre-shared keys used for DTLS negotiation SHOULD be shared only by
the pair of endpoints; otherwise, security could be attacked by
diverting messages to another endpoint holding that pre-shared key.
4.5. Composite Security
Composite Security (SType = 3) is the combination of DTLS Pairwise
Security and IS-IS CRYPTO_AUTH-Based Authentication. On
transmission, the DTLS record or records to be sent are secured as
specified in Section 4.4 then used as the payload for the application
of Authentication as specified in Section 4.3. On reception, the
IS-IS CRYPTO_AUTH-based authentication is verified first and an error
is returned if it fails. If the IS-IS CRYPTO_AUTH-based
authentication succeeds, then the DTLS record or records are
processed.
An advantage of Composite Security is that the payload is
authenticated and encrypted with a modern security protocol; in
addition, the RBridge Channel Header and (except in the native case)
preceding the MAC addresses and Data Label are provided with some
authentication.
5. Extended RBridge Channel Errors
RBridge Channel Header Extension errors are reported like RBridge
Channel errors. The ERR field is set to one of the following error
codes:
Value RBridge Channel Error Code Meaning
----- ------------------------------------
6 Unknown or unsupported field value
7 Authentication failure
8 Error in nested RBridge Channel message
Table 3: Additional ERR Values
Eastlake, et al. Standards Track [Page 18]
RFC 7978 TRILL: RBridge Channel Extension September 2016
5.1. SubERRs
If the ERR field is 6, the SubERR field indicates the problematic
field or value as shown in the table below. At this time no
suberrror codes are assigned under any other ERR field value.
Err SubERR Meaning (for ERR = 6)
--- ------ -----------------------
0 No Error; suberrors not allowed
1-5 (no suberrors assigned)
6 0 Reserved
6 1 Non-zero RESV4 nibble
6 2 Unsupported SType
6 3 Unsupported PType
6 4 Unknown Key ID
6 5 Unsupported Ethertype with PType = 2
6 6 Unsupported authentication algorithm for SType = 1
6 7 Non-zero SubERR with zero ERR field
7-14 (no suberrors assigned)
15 Reserved
Table 4: SubERR Values
5.2. Secure Nested RBridge Channel Errors
If
o an extended RBridge Channel message is sent with security and with
a payload type (PType) indicating an Ethertyped payload and the
Ethertype indicates a nested RBridge Channel message and
o there is an error in the processing of that nested message that
results in a return RBridge Channel message with a non-zero ERR
field,
then that returned message SHOULD also be nested in an extended
RBridge Channel message using the same type of security. In this
case, the ERR field in the Extended RBridge Channel envelope is set
to 8 indicating that there is a nested error in the message being
tunneled back.
6. IANA Considerations
6.1. Extended RBridge Channel Protocol Number
IANA has assigned 0x004 from the range assigned by Standards Action
[RFC5226] as the RBridge Channel protocol number to indicate RBridge
Channel Header Extension.
Eastlake, et al. Standards Track [Page 19]
RFC 7978 TRILL: RBridge Channel Extension September 2016
The added "RBridge Channel Protocols" registry in the TRILL
Parameters registry is as follows:
Protocol Description Reference
-------- -------------------------- ----------------
0x004 RBridge Channel Extension RFC 7978
6.2. RBridge Channel Protocol Subregistries
IANA has created three subregistries under the "RBridge Channel
Protocols" registry as detailed in the subsections below.
6.2.1. RBridge Channel Error Codes
IANA has assigned three additional code points in the "RBridge
Channel Error Codes" subregistry in the "Transparent Interconnection
of Lots of Links (TRILL) Parameters" registry. The additional
entries are as shown in Table 3 in Section 5 and the "Reference"
column value is "RFC 7978" for those rows.
6.2.2. RBridge Channel SubError Codes
IANA has created a subregistry indented under the "RBridge Channel
Error Codes" registry, for RBridge Channel SubError Codes. The
initial contents of this subregistry are shown in Table 4 in Section
5.1 and the fourth column "Reference" includes value "RFC 7978" for
all rows. The header information is as follows:
Registry Name: RBridge Channel SubError Codes
Registration Procedures: IETF Review
Reference: RFC 7978
6.2.3. Extended RBridge Channel Payload Types Subregistry
IANA has created an "Extended RBridge Channel Payload Types"
subregistry after the "RBridge Channel Protocols" registry in the
"Transparent Interconnection of Lots of Links (TRILL) Parameters"
registry. The header information is as follows:
Registration Procedures: IETF Review
Reference: RFC 7978
The initial registry content is in Table 1 in Section 3 of this
document.
Eastlake, et al. Standards Track [Page 20]
RFC 7978 TRILL: RBridge Channel Extension September 2016
6.2.4. Extended RBridge Channel Security Types Subregistry
IANA has created an "Extended RBridge Channel Security Types"
subregistry after the "Extended RBridge Channel Payload Types"
registry in the "Transparent Interconnection of Lots of Links (TRILL)
Parameters" registry. The header information is as follows:
Registration Procedures: IETF Review
Reference: RFC 7978
The initial registry content is in Table 2 in Section 4 of this
document.
7. Security Considerations
The RBridge Channel Header Extension has potentially positive and
negative effects on security.
On the positive side, it provides optional security that can be used
to authenticate and/or encrypt RBridge Channel messages. Some
RBridge Channel message payloads, such as BFD [RFC7175], provide
their own security but where this is not true, consideration should
be given, when specifying an RBridge Channel protocol, to
recommending or requiring use of the security features of the RBridge
Channel Header Extension.
On the negative side, the optional ability to tunnel more payload
types, and to tunnel them between TRILL switches and to and from end
stations, can increase risk unless precautions are taken. The
processing of decapsulated extended RBridge Channel payloads is a
place where you SHOULD NOT be liberal in what you accept. This is
because the tunneling facility makes it easier for unexpected
messages to pop up in unexpected places in a TRILL campus due to
accidents or the actions of an adversary. Local policies SHOULD
generally be strict and only accept payload types required and then
only with adequate security for the particular circumstances.
See the first paragraph of Section 4 for recommendations on SType
usage.
See [RFC7457] for security considerations of DTLS.
If IS-IS authentication is not being used, then IS-IS CRYPTO_AUTH
keying material [RFC5310] would not normally be available but that
presumably represents a judgment by the TRILL campus operator that no
security is needed.
Eastlake, et al. Standards Track [Page 21]
RFC 7978 TRILL: RBridge Channel Extension September 2016
See [RFC7178] for general RBridge Channel security considerations and
[RFC6325] for general TRILL security considerations.
8. Normative References
[IS-IS] International Organization for Standardization,
"Information technology -- Telecommunications and
information exchange between systems -- 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)", ISO/IEC 10589:2002, Second Edition, 2002.
[RFC20] Cerf, V., "ASCII format for network interchange", STD 80,
RFC 20, DOI 10.17487/RFC0020, October 1969,
<http://www.rfc-editor.org/info/rfc20>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC4279] Eronen, P., Ed., and H. Tschofenig, Ed., "Pre-Shared Key
Ciphersuites for Transport Layer Security (TLS)", RFC 4279,
DOI 10.17487/RFC4279, December 2005,
<http://www.rfc-editor.org/info/rfc4279>.
[RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
and M. Fanto, "IS-IS Generic Cryptographic Authentication",
RFC 5310, DOI 10.17487/RFC5310,v February 2009,
<http://www.rfc-editor.org/info/rfc5310>.
[RFC5869] Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand
Key Derivation Function (HKDF)", RFC 5869,
DOI 10.17487/RFC5869, May 2010,
<http://www.rfc-editor.org/info/rfc5869>.
[RFC6325] Perlman, R., Eastlake 3rd, D., Dutt, D., Gai, S., and A.
Ghanwani, "Routing Bridges (RBridges): Base Protocol
Specification", RFC 6325, DOI 10.17487/RFC6325, July 2011,
<http://www.rfc-editor.org/info/rfc6325>.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <http://www.rfc-editor.org/info/rfc6347>.
Eastlake, et al. Standards Track [Page 22]
RFC 7978 TRILL: RBridge Channel Extension September 2016
[RFC7172] Eastlake 3rd, D., Zhang, M., Agarwal, P., Perlman, R., and
D. Dutt, "Transparent Interconnection of Lots of Links
(TRILL): Fine-Grained Labeling", RFC 7172,
DOI 10.17487/RFC7172, May 2014,
<http://www.rfc-editor.org/info/rfc7172>.
[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,
DOI 10.17487/RFC7176, May 2014,
<http://www.rfc-editor.org/info/rfc7176>.
[RFC7178] Eastlake 3rd, D., Manral, V., Li, Y., Aldrin, S., and D.
Ward, "Transparent Interconnection of Lots of Links
(TRILL): RBridge Channel Support", RFC 7178,
DOI 10.17487/RFC7178, May 2014,
<http://www.rfc-editor.org/info/rfc7178>.
[RFC7356] Ginsberg, L., Previdi, S., and Y. Yang, "IS-IS Flooding
Scope Link State PDUs (LSPs)", RFC 7356,
DOI 10.17487/RFC7356, September 2014,
<http://www.rfc-editor.org/info/rfc7356>.
[RFC7780] Eastlake 3rd, D., Zhang, M., Perlman, R., Banerjee, A.,
Ghanwani, A., and S. Gupta, "Transparent Interconnection of
Lots of Links (TRILL): Clarifications, Corrections, and
Updates", RFC 7780, DOI 10.17487/RFC7780, February 2016,
<http://www.rfc-editor.org/info/rfc7780>.
9. Informative References
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<http://www.rfc-editor.org/info/rfc5226>.
[RFC6234] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
(SHA and SHA-based HMAC and HKDF)", RFC 6234,
DOI 10.17487/RFC6234, May 2011,
<http://www.rfc-editor.org/info/rfc6234>.
[RFC6361] Carlson, J. and D. Eastlake 3rd, "PPP Transparent
Interconnection of Lots of Links (TRILL) Protocol Control
Protocol", RFC 6361, DOI 10.17487/RFC6361, August 2011,
<http://www.rfc-editor.org/info/rfc6361>.
Eastlake, et al. Standards Track [Page 23]
RFC 7978 TRILL: RBridge Channel Extension September 2016
[RFC7042] Eastlake 3rd, D. and J. Abley, "IANA Considerations and
IETF Protocol and Documentation Usage for IEEE 802
Parameters", BCP 141, RFC 7042, DOI 10.17487/RFC7042,
October 2013, <http://www.rfc-editor.org/info/rfc7042>.
[RFC7067] Dunbar, L., Eastlake 3rd, D., Perlman, R., and I.
Gashinsky, "Directory Assistance Problem and High-Level
Design Proposal", RFC 7067, DOI 10.17487/RFC7067, November
2013, <http://www.rfc-editor.org/info/rfc7067>.
[RFC7175] Manral, V., Eastlake 3rd, D., Ward, D., and A. Banerjee,
"Transparent Interconnection of Lots of Links (TRILL):
Bidirectional Forwarding Detection (BFD) Support",
RFC 7175, DOI 10.17487/RFC7175, May 2014,
<http://www.rfc-editor.org/info/rfc7175>.
[RFC7457] Sheffer, Y., Holz, R., and P. Saint-Andre, "Summarizing
Known Attacks on Transport Layer Security (TLS) and
Datagram TLS (DTLS)", RFC 7457, DOI 10.17487/RFC7457,
February 2015, <http://www.rfc-editor.org/info/rfc7457>.
[AddrFlush]
Hao, W., Eastlake, D., and Y. Li, "TRILL: Address Flush
Message", Work in Progress, draft-ietf-trill-address-
flush-00, May 2016.
[GroupKey]
Eastlake, D., "TRILL: Group Keying", Work in Progress,
draft-eastlake-trill-group-keying-00, July 2016.
[TRILL-AF]
Eastlake, D., Li, Y., Umair, M., Banerjee, A., and F. Hu,
"TRILL: Appointed Forwarders", Work in Progress,
draft-ietf-trill-rfc6439bis-03, August 2016.
Eastlake, et al. Standards Track [Page 24]
RFC 7978 TRILL: RBridge Channel Extension September 2016
Acknowledgements
The contributions of the following are hereby gratefully
acknowledged:
Stephen Farrell, Jonathan Hardwick, Susan Hares, Gayle Noble, Alvaro
Retana, Yaron Sheffer, and Peter Yee.
Authors' Addresses
Donald E. Eastlake, 3rd
Huawei Technologies
155 Beaver Street
Milford, MA 01757
United States of America
Phone: +1-508-333-2270
Email: d3e3e3@gmail.com
Mohammed Umair
IPinfusion
Email: mohammed.umair2@gmail.com
Yizhou Li
Huawei Technologies
101 Software Avenue
Nanjing 210012
China
Phone: +86-25-56622310
Email: liyizhou@huawei.com
Eastlake, et al. Standards Track [Page 25]
ERRATA
