Carrying Link-State Information in BGP
This specification contains two parts:
-
Definition of a new BGP NLRI that describes links, nodes, and prefixes comprising of IGP link-state information
-
Definition of a new BGP path attribute (BGP-LS attribute) that carries link, node, and prefix properties and attributes, such as the link and prefix metric or auxiliary Router- IDs of nodes ,and so on.
TLV Format
Information in the new Link-State NLRIs and attributes is encoded in Type/Length/Value (TLV) triplets. The TLV format is shown in the below figure.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Value (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Length field defines the length of the value portion in octets (thus, a TLV with no value portion would have a length of zero).
Link-State NLRI
The MP_REACH_NLRI and MP_UNREACH_NLRI attributes are BGP's containers for carrying opaque information. Each Link-State Network Layer Reachability Information (NLRI) describes either a node, a link, or a prefix. NLRI body is a set of Type/Length/Value triplets (TLV) and contains the data that identifies an object.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NLRI Type | Total NLRI Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Link-State NLRI (variable) //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NLRI Types
The Total NLRI length field contains the cumulative length, in octets, of the rest of the NLRI, not including the NLRI Type field or itself.Figure 2. The NLRI Types
+------+---------------------------+
| Type | NLRI Type |
+------+---------------------------+
| 1 | Node NLRI |
| 2 | Link NLRI |
| 3 | IPv4 Topology Prefix NLRI |
| 4 | IPv6 Topology Prefix NLRI |
+------+---------------------------+
The NLRI Types are shown in the following figures:Figure 3. The Node NLRI Format
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
+-+-+-+-+-+-+-+-+
| Protocol-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identifier |
| (64 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Local Node Descriptors (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4. The Link NLRI Format
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
+-+-+-+-+-+-+-+-+
| Protocol-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identifier |
| (64 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Local Node Descriptors (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Remote Node Descriptors (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Link Descriptors (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The IPv4 and IPv6 Prefix NLRIs (NLRI Type = 3 and Type = 4) use the same format, as shown in the following figure.Figure 5. The IPv4/IPv6 Topology Prefix NLRI Format
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
+-+-+-+-+-+-+-+-+
| Protocol-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identifier |
| (64 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Local Node Descriptors (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Prefix Descriptors (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Node Descriptors
Each link is anchored by a pair of Router-IDs that are used by the underlying IGP, namely, a 48-bit ISO System-ID for IS-IS and a 32-bit Router-ID for OSPFv2 and OSPFv3. An IGP may use one or more additional auxiliary Router-IDs, mainly for traffic engineering purposes. For example, IS-IS may have one or more IPv4 and IPv6 TE Router-IDs. These auxiliary Router-IDs must be included in the link attribute.
Link Descriptors
The Link Descriptor field is a set of Type/Length/Value (TLV) triplets. The link descriptor TLVs uniquely identify a link among multiple parallel links between a pair of anchor routers. A link described by the link descriptor TLVs actually is a "half-link", a unidirectional representation of a logical link. In order to fully describe a single logical link, two originating routers advertise a half-link each, that is, two Link NLRIs are advertised for a given point-to-point link.
Prefix Descriptors
The Prefix Descriptor field is a set of Type/Length/Value (TLV) triplets. Prefix Descriptor TLVs uniquely identify an IPv4 or IPv6 prefix originated by a node.
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. This attribute should only be included with Link-State NLRIs. This attribute must be ignored for all other address families.
BGP-LS OSPF
OSPF is one of the IGP protocols that feeds its topology into BGP into the LS cache. Link state information can be passed to BGP in two ways:
-
When new communications between OSPF and BGP has been established, or when BGP-LS functionality has been initially enabled under OSPF, then all LSA information is downloaded to BGP via the LS library.
-
As new LSA information is being processed or received from remote OSPF nodes, this information is added or updated in BGP.
Configuring BGP-LS OSPF
Perform the following steps to configure OSPF with BGP-LS:
-
Enable the OSPF routing protocol and enter router configuration mode.
router ospf
For example,Device(config-router)# router ospf 10
-
Distribute BGP link-state.
distribute link-state
For example,Device(config-router)# distribute link-state instance-id <instid>
Device(config-router)# distribute link-state throttle <time>
instance-id (optional): Sets instance ID for LS distribution. Default Value is 0. Range: 32 to 2^32-1.
throttle (optional): Sets throttle time to process LS distribution queue. Default value is 5 seconds. Range: 1 to 3600 seconds.
Note
In the scenarios where any area gets deleted, throttle timer does not get honored. Queue is walked by OSPF completely and updates to all the areas are sent to BGP.
If you do not specify any value for instance ID and throttle, default values are taken.
Example:
#show run | sec router ospf router ospf 10 distribute link-state instance-id 33 throttle 6
| Note |
You should not be using the same instance ID for two OSPF instances. It throws an instance ID already in use error. |
BGP-LS IS-IS
IS-IS distributes routing information into BGP. IS-IS processes the routing information in it's LSP database and extract the relevant objects. It advertises IS-IS nodes, links, and prefix information and their attributes into BGP. This update from IS-IS into BGP only happens when there is a change in the LSP fragments, either belonging to the local router or any remote routers.
Configuring IS-IS With BGP-LS
Perform the following steps to configure IS-IS with BGP-LS:
-
Enable the IS-IS routing protocol and enter router configuration mode.
router isis
For example,Device(config-router)# router isis
-
Distribute BGP link-state.
distribute link-state
For example,Device(config-router)# distribute link-state instance-id <instid>
Device(config-router)# distribute link-state throttle <time>
instance-id (optional): Sets instance ID for LS distribution. Range: 32-4294967294.
throttle (optional): Sets throttle time to process LS distribution queue. Range: 5-20 seconds.
Configuring BGP
Perform the following steps to configure BGP with BGP-LS:
-
Enable the BGP routing protocol and enter router configuration mode.
router bgp
For example,Device(config-if)# router bgp 100
-
Configure the address-family link-state.
address-family link-state link-state
For example,Device(config-router)# address-family link-state link-state
-
Exit the address-family.
exit-address-family
For example,Device(config-router)# exit-address-family
Example: ISIS With BGP-LS Configuration
Example: IS-IS Configuration
router isis 1 net 49.0001.1720.1600.1001.00 is-type level-1 metric-style wide distribute link-state level-1 segment-routing mpls segment-routing prefix-sid-map advertise-local mpls traffic-eng router-id Loopback0 mpls traffic-eng level-1 interface GigabitEthernet2/2/2 ip address 30.0.0.2 255.255.255.0 ip router isis 1 negotiation auto mpls traffic-eng tunnels isis network point-to-point
Example: BGP Configuration
router bgp 100 bgp log-neighbor-changes neighbor 19.0.0.6 remote-as 100 neighbor 19.0.0.79 remote-as 100 ! address-family ipv4 neighbor 19.0.0.6 activate neighbor 19.0.0.79 activate exit-address-family ! address-family link-state link-state neighbor 19.0.0.6 activate neighbor 19.0.0.79 activate exit-address-family
BGP-LS Show Commands
show ip ospf ls-distribution
Displays the status of LS distribution.
R1#show ip ospf ls-distribution
OSPF Router with ID (1.3.0.1) (Process ID 10)
OSPF LS Distribution is Enabled
Instance Id: 0
Throttle time: 5
Registration Handle: 0x0
Status:Ready Active
Num DBs Queued for LSCache Update: 0
Num of DBs with Unresolved Links: 0
show ip ospf database dist-ls-pending
Displays the LSAs that are pending, to be sent to BGP.
Sample Output:
R1#show ip ospf database dist-ls-pending
OSPF Router with ID (1.3.0.1) (Process ID 10)
Router Link States (Area 0)
Link ID ADV Router Age Seq# Checksum Link count
1.2.0.2 1.2.0.2 4 0x80000006 0x009678 1
3.3.3.3 3.3.3.3 1110 0x80000018 0x00CAF9 2 (Has-unresolved-links)
show isis distribute-ls [level-1 | level-2]
Displays ISIS internal LS cache information that are distributed to BGP.
r1#sh isis distribute-ls
ISIS distribute link-state: configured
distls_levels:0x3, distls_initialized:1,
distls_instance_id:0, distls_throttle_delay:10
LS DB: ls_init_started(0) ls_initialized(1) ls_pending_delete(0)
distls_enabled[1]:1
distls_enabled[2]:1
Level 1:
Node System ID:0003.0003.0003 Pseudonode-Id:0 ls_change_flags:0x0
LSP: lspid(0003.0003.0003.00-00), lsptype(0) lsp_change_flags(0x0)
Node Attr: name(r3) bitfield(0xD1) node_flags(0x0)
area_len/area_addr(2/33) num_mtid/mtid(0/0) ipv4_id(33.33.33.1)
num_alg/sr_alg(0/0) num_srgb/srgb(1/(start:16000, range:8000)
srgb_flags(0x80)
opaqe_len/opaqe(0/0x0)
ISIS LS Links:
mtid(0): nid:0002.0002.0002.00, {0, 0}, {6.6.6.1, 6.6.6.6}
Link Attr: bitbfield:0x940F, local_ipv4_id:6.6.6.1, remote_ipv4_id:6.6.6.6,
max_link_bw:10000, max_resv_bw:10000,
num_unresv_bw/unresv_bw:8/
[0]: 10000 kbits/sec, [1]: 8000 kbits/sec
[2]: 8000 kbits/sec, [3]: 8000 kbits/sec
[4]: 8000 kbits/sec, [5]: 8000 kbits/sec
[6]: 8000 kbits/sec, [7]: 8000 kbits/sec,
admin_group:0, protect_type:0, mpls_proto_mask:0x0,
te_metric:0, metric:0, link_name:,
num_srlg/srlg:0/
num_adj_sid/adjsid:2/
Adjacency SID Label:16 F:0 B:0 V:1 L:1 S:0 weight:0
Adjacency SID Label:17 F:0 B:1 V:1 L:1 S:0 weight:0
opaque_len/opaque_data:0/0x0
Address-family ipv4 ISIS LS Prefix:
mtid(0): 1.1.1.0/24
Prefix Attr: bitfield:0x0, metric:10, igp_flags:0x0,
num_route_tag:0, route_tag:0
num_pfx_sid:0, pfx_sid:
pfx_srms:
opaque_len:0, opaque_data:0x0
mtid(0): 3.3.3.0/24
Prefix Attr: bitfield:0x0, metric:10, igp_flags:0x0,
num_route_tag:0, route_tag:0
num_pfx_sid:0, pfx_sid:
pfx_srms:
opaque_len:0, opaque_data:0x0
show bgp link-state link-state
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,
x best-external, a additional-path, c RIB-compressed,
t secondary path,
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found
Prefix codes:E link, V node, T4 IPv4 reachable route, T6 IPv6 reachable route, I Identifier,
N local node, R remote node, L link, P prefix,
L1/L2 ISIS level-1/level-2, O OSPF, a area-ID, l link-ID,
t topology-ID, s ISO-ID, c confed-ID/ASN, b bgp-identifier,
r router-ID, i if-address, n nbr-address, o OSPF Route-type,
p IP-prefix, d designated router address, u/U Unknown,
x/X Unexpected, m/M Malformed
Network Next Hop Metric LocPrf Weight Path
*> [V][L1][I0x43][N[c100][b0.0.0.0][s1720.1600.1001.00]]
15.0.0.1 0 0 100 i
*> [V][L1][I0x43][N[c100][b0.0.0.0][s1720.1600.2002.00]]
15.0.0.1 0 0 100 i
*> [V][L1][I0x43][N[c100][b0.0.0.0][s1720.1600.3003.00]]
15.0.0.1 0 0 100 i
*> [V][L1][I0x43][N[c100][b0.0.0.0][s1720.1600.4004.00]]
15.0.0.1 0 0 100 i
*> [V][L1][I0x43][N[c100][b0.0.0.0][s1720.1600.5005.00]]
15.0.0.1 0 0 100 i
*> [E][L1][I0x43][N[c100][b0.0.0.0][s1720.1600.1001.00]][R[c100][b0.0.0.0][s1720.1600.2002.00]][L]
15.0.0.1 0 0 100 i
*> [E][L1][I0x43][N[c100][b0.0.0.0][s1720.1600.2002.00]][R[c100][b0.0.0.0][s1720.1600.1001.00]][L]
15.0.0.1 0 0 100 i
*> [E][L1][I0x43][N[c100][b0.0.0.0][s1720.1600.2002.00]][R[c100][b0.0.0.0][s1720.1600.3003.00]][L]
15.0.0.1 0 0 100 i
*> [E][L1][I0x43][N[c100][b0.0.0.0][s1720.1600.2002.00]][R[c100][b0.0.0.0][s1720.1600.4004.00]][L]
15.0.0.1 0 0 100 i
*> [E][L1][I0x43][N[c100][b0.0.0.0][s1720.1600.3003.00]][R[c100][b0.0.0.0][s1720.1600.2002.00]][L]
15.0.0.1 0 0 100 i
*> [E][L1][I0x43][N[c100][b0.0.0.0][s1720.1600.3003.00]][R[c100][b0.0.0.0][s1720.1600.5005.00]][L]
15.0.0.1 0 0 100 i
*> [E][L1][I0x43][N[c100][b0.0.0.0][s1720.1600.4004.00]][R[c100][b0.0.0.0][s1720.1600.2002.00]][L]
15.0.0.1 0 0 100 i
*> [E][L1][I0x43][N[c100][b0.0.0.0][s1720.1600.4004.00]][R[c100][b0.0.0.0][s1720.1600.5005.00]][L]
15.0.0.1 0 0 100 i
*> [E][L1][I0x43][N[c100][b0.0.0.0][s1720.1600.5005.00]][R[c100][b0.0.0.0][s1720.1600.3003.00]][L]
15.0.0.1 0 0 100 i
*> [E][L1][I0x43][N[c100][b0.0.0.0][s1720.1600.5005.00]][R[c100][b0.0.0.0][s1720.1600.4004.00]][L]
15.0.0.1 0 0 100 i
*> [T4][L1][I0x43][N[c100][b0.0.0.0][s1720.1600.1001.00]][P[p10.0.0.0/24]]
15.0.0.1 0 0 100 i
*> [T4][L1][I0x43][N[c100][b0.0.0.0][s1720.1600.1001.00]][P[p7.7.7.7/32]]
15.0.0.1 0 0 100 i
*> [T4][L1][I0x43][N[c100][b0.0.0.0][s1720.1600.2002.00]][P[p10.0.0.0/24]]
15.0.0.1 0 0 100 i
*> [T4][L1][I0x43][N[c100][b0.0.0.0][s1720.1600.2002.00]][P[p11.0.0.0/24]]
15.0.0.1 0 0 100 i
*> [T4][L1][I0x43][N[c100][b0.0.0.0][s1720.1600.2002.00]][P[p12.0.0.0/24]]
15.0.0.1 0 0 100 i
*> [T4][L1][I0x43][N[c100][b0.0.0.0][s1720.1600.2002.00]][P[p5.5.5.5/32]]
15.0.0.1 0 0 100 i
*> [T4][L1][I0x43][N[c100][b0.0.0.0][s1720.1600.3003.00]][P[p11.0.0.0/24]]
15.0.0.1 0 0 100 i
*> [T4][L1][I0x43][N[c100][b0.0.0.0][s1720.1600.3003.00]][P[p13.0.0.0/24]]
15.0.0.1 0 0 100 i
*> [T4][L1][I0x43][N[c100][b0.0.0.0][s1720.1600.3003.00]][P[p3.3.3.3/32]]
15.0.0.1 0 0 100 i
*> [T4][L1][I0x43][N[c100][b0.0.0.0][s1720.1600.4004.00]][P[p12.0.0.0/24]]
15.0.0.1 0 0 100 i
*> [T4][L1][I0x43][N[c100][b0.0.0.0][s1720.1600.4004.00]][P[p14.0.0.0/24]]
15.0.0.1 0 0 100 i
*> [T4][L1][I0x43][N[c100][b0.0.0.0][s1720.1600.4004.00]][P[p15.15.15.15/32]]
15.0.0.1 0 0 100 i
*> [T4][L1][I0x43][N[c100][b0.0.0.0][s1720.1600.5005.00]][P[p13.0.0.0/24]]
15.0.0.1 0 0 100 i
*> [T4][L1][I0x43][N[c100][b0.0.0.0][s1720.1600.5005.00]][P[p14.0.0.0/24]]
15.0.0.1 0 0 100 i
*> [T4][L1][I0x43][N[c100][b0.0.0.0][s1720.1600.5005.00]][P[p15.0.0.0/24]]
15.0.0.1 0 0 100 i
*> [T4][L1][I0x43][N[c100][b0.0.0.0][s1720.1600.5005.00]][P[p16.16.16.16/32]]
15.0.0.1 0 0 100 i
show bgp link-state link-state nlri <nlri string>
BGP routing table entry for [V][L1][I0x43][N[c100][b0.0.0.0][s1720.1600.4004.00]], version 95
Paths: (1 available, best #1, table link-state link-state)
Not advertised to any peer
Refresh Epoch 4
Local
16.16.16.16 (metric 30) from 15.15.15.15 (15.15.15.15)
Origin IGP, metric 0, localpref 100, valid, internal, best
Originator: 16.16.16.16, Cluster list: 15.15.15.15
LS Attribute: Node-name: R4, ISIS area: 49.12.34
rx pathid: 0, tx pathid: 0x0
BGP-LS Debug Commands
-
debug ip ospf dist-ls [detail]
Turns on ls-distribution related debugs in OSPF.
-
debug isis distribute-ls
Displays the items being advertised into the BGP from IS-IS.