3.3 The BGP-LS Attribute
3.3. The BGP-LS Attribute
The BGP-LS attribute is an optional, non-transitive BGP attribute
that is used to carry link, node, and prefix parameters and
attributes. It is defined as a set of Type/Length/Value (TLV)
triplets, described in the following section. This attribute SHOULD
only be included with Link-State NLRIs. This attribute MUST be
ignored for all other address families.
Node attribute TLVs are the TLVs that may be encoded in the BGP-LS
attribute with a Node NLRI. The following Node Attribute TLVs are
defined:
+-------------+----------------------+----------+-------------------+
| TLV Code | Description | Length | Reference |
| Point | | | (RFC/Section) |
+-------------+----------------------+----------+-------------------+
| 263 | Multi-Topology | variable | Section 3.2.1.5 |
| | Identifier | | |
| 1024 | Node Flag Bits | 1 | Section 3.3.1.1 |
| 1025 | Opaque Node | variable | Section 3.3.1.5 |
| | Attribute | | |
| 1026 | Node Name | variable | Section 3.3.1.3 |
| 1027 | IS-IS Area | variable | Section 3.3.1.2 |
| | Identifier | | |
| 1028 | IPv4 Router-ID of | 4 | [RFC5305]/4.3 |
| | Local Node | | |
| 1029 | IPv6 Router-ID of | 16 | [RFC6119]/4.1 |
| | Local Node | | |
+-------------+----------------------+----------+-------------------+
Table 7: Node Attribute TLVs
The Node Flag Bits TLV carries a bit mask describing node attributes.
The value is a variable-length bit array of flags, where each bit
represents a node capability.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|O|T|E|B|R|V| Rsvd|
+-+-+-+-+-+-+-+-+-+
Figure 15: Node Flag Bits TLV Format
The bits are defined as follows:
+-----------------+-------------------------+------------+
| Bit | Description | Reference |
+-----------------+-------------------------+------------+
| 'O' | Overload Bit | [ISO10589] |
| 'T' | Attached Bit | [ISO10589] |
| 'E' | External Bit | [RFC2328] |
| 'B' | ABR Bit | [RFC2328] |
| 'R' | Router Bit | [RFC5340] |
| 'V' | V6 Bit | [RFC5340] |
| Reserved (Rsvd) | Reserved for future use | |
+-----------------+-------------------------+------------+
Table 8: Node Flag Bits Definitions
An IS-IS node can be part of one or more IS-IS areas. Each of these
area addresses is carried in the IS-IS Area Identifier TLV. If
multiple area addresses are present, multiple TLVs are used to encode
them. The IS-IS Area Identifier TLV may be present in the BGP-LS
attribute only when advertised in the Link-State Node NLRI.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Area Identifier (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 16: IS-IS Area Identifier TLV Format
The Node Name TLV is optional. Its structure and encoding has been
borrowed from [RFC5301]. The Value field identifies the symbolic
name of the router node. This symbolic name can be the Fully
Qualified Domain Name (FQDN) for the router, it can be a subset of
the FQDN (e.g., a hostname), or it can be any string operators want
to use for the router. The use of FQDN or a subset of it is strongly
RECOMMENDED. The maximum length of the Node Name TLV is 255 octets.
The Value field is encoded in 7-bit ASCII. If a user interface for
configuring or displaying this field permits Unicode characters, that
user interface is responsible for applying the ToASCII and/or
ToUnicode algorithm as described in [RFC5890] to achieve the correct
format for transmission or display.
Although [RFC5301] describes an IS-IS-specific extension, usage of
the Node Name TLV is possible for all protocols. How a router
derives and injects node names, e.g., OSPF nodes, is outside of the
scope of this document.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Node Name (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 17: Node Name Format
The local IPv4/IPv6 Router-ID TLVs are used to describe auxiliary
Router-IDs that the IGP might be using, e.g., for TE and migration
purposes such as correlating a Node-ID between different protocols.
If there is more than one auxiliary Router-ID of a given type, then
each one is encoded in its own TLV.
The Opaque Node Attribute TLV is an envelope that transparently
carries optional Node Attribute TLVs advertised by a router. An
originating router shall use this TLV for encoding information
specific to the protocol advertised in the NLRI header Protocol-ID
field or new protocol extensions to the protocol as advertised in the
NLRI header Protocol-ID field for which there is no protocol-neutral
representation in the BGP Link-State NLRI. The primary use of the
Opaque Node Attribute TLV is to bridge the document lag between,
e.g., a new IGP link-state attribute being defined and the protocol-
neutral BGP-LS extensions being published. A router, for example,
could use this extension in order to advertise the native protocol's
Node Attribute TLVs, such as the OSPF Router Informational
Capabilities TLV defined in [RFC7770] or the IGP TE Node Capability
Descriptor TLV described in [RFC5073].
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Opaque node attributes (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 18: Opaque Node Attribute Format
Link Attribute TLVs are TLVs that may be encoded in the BGP-LS
attribute with a Link NLRI. Each 'Link Attribute' is a Type/Length/
Value (TLV) triplet formatted as defined in Section 3.1. The format
and semantics of the Value fields in some Link Attribute TLVs
correspond to the format and semantics of the Value fields in IS-IS
Extended IS Reachability sub-TLVs, defined in [RFC5305] and
[RFC5307]. Other Link Attribute TLVs are defined in this document.
Although the encodings for Link Attribute TLVs were originally
defined for IS-IS, the TLVs can carry data sourced by either IS-IS or
OSPF.
The following Link Attribute TLVs are valid in the BGP-LS attribute
with a Link NLRI:
+-----------+---------------------+--------------+------------------+
| TLV Code | Description | IS-IS TLV | Reference |
| Point | | /Sub-TLV | (RFC/Section) |
+-----------+---------------------+--------------+------------------+
| 1028 | IPv4 Router-ID of | 134/--- | [RFC5305]/4.3 |
| | Local Node | | |
| 1029 | IPv6 Router-ID of | 140/--- | [RFC6119]/4.1 |
| | Local Node | | |
| 1030 | IPv4 Router-ID of | 134/--- | [RFC5305]/4.3 |
| | Remote Node | | |
| 1031 | IPv6 Router-ID of | 140/--- | [RFC6119]/4.1 |
| | Remote Node | | |
| 1088 | Administrative | 22/3 | [RFC5305]/3.1 |
| | group (color) | | |
| 1089 | Maximum link | 22/9 | [RFC5305]/3.4 |
| | bandwidth | | |
| 1090 | Max. reservable | 22/10 | [RFC5305]/3.5 |
| | link bandwidth | | |
| 1091 | Unreserved | 22/11 | [RFC5305]/3.6 |
| | bandwidth | | |
| 1092 | TE Default Metric | 22/18 | Section 3.3.2.3 |
| 1093 | Link Protection | 22/20 | [RFC5307]/1.2 |
| | Type | | |
| 1094 | MPLS Protocol Mask | --- | Section 3.3.2.2 |
| 1095 | IGP Metric | --- | Section 3.3.2.4 |
| 1096 | Shared Risk Link | --- | Section 3.3.2.5 |
| | Group | | |
| 1097 | Opaque Link | --- | Section 3.3.2.6 |
| | Attribute | | |
| 1098 | Link Name | --- | Section 3.3.2.7 |
+-----------+---------------------+--------------+------------------+
Table 9: Link Attribute TLVs
The local/remote IPv4/IPv6 Router-ID TLVs are used to describe
auxiliary Router-IDs that the IGP might be using, e.g., for TE
purposes. All auxiliary Router-IDs of both the local and the remote
node MUST be included in the link attribute of each Link NLRI. If
there is more than one auxiliary Router-ID of a given type, then
multiple TLVs are used to encode them.
The MPLS Protocol Mask TLV carries a bit mask describing which MPLS
signaling protocols are enabled. The length of this TLV is 1. The
value is a bit array of 8 flags, where each bit represents an MPLS
Protocol capability.
Generation of the MPLS Protocol Mask TLV is only valid for and SHOULD
only be used with originators that have local link insight, for
example, the Protocol-IDs 'Static configuration' or 'Direct' as per
Table 2. The MPLS Protocol Mask TLV MUST NOT be included in NLRIs
with the other Protocol-IDs listed in Table 2.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L|R| Reserved |
+-+-+-+-+-+-+-+-+
Figure 19: MPLS Protocol Mask TLV
The following bits are defined:
+------------+------------------------------------------+-----------+
| Bit | Description | Reference |
+------------+------------------------------------------+-----------+
| 'L' | Label Distribution Protocol (LDP) | [RFC5036] |
| 'R' | Extension to RSVP for LSP Tunnels | [RFC3209] |
| | (RSVP-TE) | |
| 'Reserved' | Reserved for future use | |
+------------+------------------------------------------+-----------+
Table 10: MPLS Protocol Mask TLV Codes
The TE Default Metric TLV carries the Traffic Engineering metric for
this link. The length of this TLV is fixed at 4 octets. If a source
protocol uses a metric width of less than 32 bits, then the high-
order bits of this field MUST be padded with zero.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TE Default Link Metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 20: TE Default Metric TLV Format
The IGP Metric TLV carries the metric for this link. The length of
this TLV is variable, depending on the metric width of the underlying
protocol. IS-IS small metrics have a length of 1 octet (the two most
significant bits are ignored). OSPF link metrics have a length of 2
octets. IS-IS wide metrics have a length of 3 octets.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// IGP Link Metric (variable length) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 21: IGP Metric TLV Format
The Shared Risk Link Group (SRLG) TLV carries the Shared Risk Link
Group information (see Section 2.3 ("Shared Risk Link Group
Information") of [RFC4202]). It contains a data structure consisting
of a (variable) list of SRLG values, where each element in the list
has 4 octets, as shown in Figure 22. The length of this TLV is 4 *
(number of SRLG values).
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Shared Risk Link Group Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// ............ //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Shared Risk Link Group Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 22: Shared Risk Link Group TLV Format
The SRLG TLV for OSPF-TE is defined in [RFC4203]. In IS-IS, the SRLG
information is carried in two different TLVs: the IPv4 (SRLG) TLV
(Type 138) defined in [RFC5307] and the IPv6 SRLG TLV (Type 139)
defined in [RFC6119]. In Link-State NLRI, both IPv4 and IPv6 SRLG
information are carried in a single TLV.
The Opaque Link Attribute TLV is an envelope that transparently
carries optional Link Attribute TLVs advertised by a router. An
originating router shall use this TLV for encoding information
specific to the protocol advertised in the NLRI header Protocol-ID
field or new protocol extensions to the protocol as advertised in the
NLRI header Protocol-ID field for which there is no protocol-neutral
representation in the BGP Link-State NLRI. The primary use of the
Opaque Link Attribute TLV is to bridge the document lag between,
e.g., a new IGP link-state attribute being defined and the 'protocol-
neutral' BGP-LS extensions being published.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Opaque link attributes (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 23: Opaque Link Attribute TLV Format
The Link Name TLV is optional. The Value field identifies the
symbolic name of the router link. This symbolic name can be the FQDN
for the link, it can be a subset of the FQDN, or it can be any string
operators want to use for the link. The use of FQDN or a subset of
it is strongly RECOMMENDED. The maximum length of the Link Name TLV
is 255 octets.
The Value field is encoded in 7-bit ASCII. If a user interface for
configuring or displaying this field permits Unicode characters, that
user interface is responsible for applying the ToASCII and/or
ToUnicode algorithm as described in [RFC5890] to achieve the correct
format for transmission or display.
How a router derives and injects link names is outside of the scope
of this document.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Link Name (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 24: Link Name TLV Format
Prefixes are learned from the IGP topology (IS-IS or OSPF) with a set
of IGP attributes (such as metric, route tags, etc.) that MUST be
reflected into the BGP-LS attribute with a prefix NLRI. This section
describes the different attributes related to the IPv4/IPv6 prefixes.
Prefix Attribute TLVs SHOULD be used when advertising NLRI types 3
and 4 only. The following Prefix Attribute TLVs are defined:
+---------------+----------------------+----------+-----------------+
| TLV Code | Description | Length | Reference |
| Point | | | |
+---------------+----------------------+----------+-----------------+
| 1152 | IGP Flags | 1 | Section 3.3.3.1 |
| 1153 | IGP Route Tag | 4*n | [RFC5130] |
| 1154 | IGP Extended Route | 8*n | [RFC5130] |
| | Tag | | |
| 1155 | Prefix Metric | 4 | [RFC5305] |
| 1156 | OSPF Forwarding | 4 | [RFC2328] |
| | Address | | |
| 1157 | Opaque Prefix | variable | Section 3.3.3.6 |
| | Attribute | | |
+---------------+----------------------+----------+-----------------+
Table 11: Prefix Attribute TLVs
The IGP Flags TLV contains IS-IS and OSPF flags and bits originally
assigned to the prefix. The IGP Flags TLV is encoded 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|D|N|L|P| Resvd.|
+-+-+-+-+-+-+-+-+
Figure 25: IGP Flag TLV Format
The Value field contains bits defined according to the table below:
+----------+---------------------------+-----------+
| Bit | Description | Reference |
+----------+---------------------------+-----------+
| 'D' | IS-IS Up/Down Bit | [RFC5305] |
| 'N' | OSPF "no unicast" Bit | [RFC5340] |
| 'L' | OSPF "local address" Bit | [RFC5340] |
| 'P' | OSPF "propagate NSSA" Bit | [RFC5340] |
| Reserved | Reserved for future use. | |
+----------+---------------------------+-----------+
Table 12: IGP Flag Bits Definitions
The IGP Route Tag TLV carries original IGP Tags (IS-IS [RFC5130] or
OSPF) of the prefix and is encoded 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Route Tags (one or more) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 26: IGP Route Tag TLV Format
Length is a multiple of 4.
The Value field contains one or more Route Tags as learned in the IGP
topology.
The Extended IGP Route Tag TLV carries IS-IS Extended Route Tags of
the prefix [RFC5130] and is encoded 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Extended Route Tag (one or more) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 27: Extended IGP Route Tag TLV Format
Length is a multiple of 8.
The Extended Route Tag field contains one or more Extended Route Tags
as learned in the IGP topology.
The Prefix Metric TLV is an optional attribute and may only appear
once. If present, it carries the metric of the prefix as known in
the IGP topology as described in Section 4 of [RFC5305] (and
therefore represents the reachability cost to the prefix). If not
present, it means that the prefix is advertised without any
reachability.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 28: Prefix Metric TLV Format
Length is 4.
The OSPF Forwarding Address TLV [RFC2328] [RFC5340] carries the OSPF
forwarding address as known in the original OSPF advertisement.
Forwarding address can be either IPv4 or IPv6.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Forwarding Address (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 29: OSPF Forwarding Address TLV Format
Length is 4 for an IPv4 forwarding address, and 16 for an IPv6
forwarding address.
The Opaque Prefix Attribute TLV is an envelope that transparently
carries optional Prefix Attribute TLVs advertised by a router. An
originating router shall use this TLV for encoding information
specific to the protocol advertised in the NLRI header Protocol-ID
field or new protocol extensions to the protocol as advertised in the
NLRI header Protocol-ID field for which there is no protocol-neutral
representation in the BGP Link-State NLRI. The primary use of the
Opaque Prefix Attribute TLV is to bridge the document lag between,
e.g., a new IGP link-state attribute being defined and the protocol-
neutral BGP-LS extensions being published.
The format of the TLV is 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Opaque Prefix Attributes (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 30: Opaque Prefix Attribute TLV Format
Type is as specified in Table 11. Length is variable.