To support segment routing, Border Gateway Protocol (BGP) requires the ability to advertise a segment identifier (SID) for
a BGP prefix. A BGP-Prefix-SID is the segment identifier of the BGP prefix segment in a segment routing network. BGP prefix
SID attribute is a BGP extension to signal BGP prefix-SIDs. However, there may be routers which do not support BGP extension
for segment routing. Hence, those routers also do not support BGP prefix SID attribute and an alternate approach is required.
BGP proxy prefix SID feature allows you to attach BGP prefix SID attributes for remote prefixes learnt from BGP labeled unicast
(LU) neighbours which are not SR-capable and propagate them as SR prefixes. This allows an LSP towards non SR endpoints to
use segment routing global block in a SR domain. Since BGP proxy prefix SID uses global label values it minimizes the use
of limited resources such as ECMP-FEC and provides more scalability for the networks.
BGP proxy prefix SID feature is implemented using the segment routing mapping server (SRMS). SRMS allows the user to configure
SID mapping entries to specify the prefix-SIDs for the prefixes. The mapping server advertises the local SID-mapping policy
to the mapping clients. BGP acts as a client of the SRMS and uses the mapping policy to calculate the prefix-SIDs.
Configuration Example:
This example shows how to configure the BGP proxy prefix SID feature for the segment routing mapping server.
RP/0/RSP0/CPU0:router(config)# segment-routing
RP/0/RSP0/CPU0:router(config-sr)# mapping-server
RP/0/RSP0/CPU0:router(config-sr-ms)# prefix-sid-map
RP/0/RSP0/CPU0:router(config-sr-ms-map)# address-family ipv4
RP/0/RSP0/CPU0:router(config-sr-ms-map-af)# 1.1.1.1/32 10 range 200
RP/0/RSP0/CPU0:router(config-sr-ms-map-af)# 192.168.64.1/32 400 range 300
This example shows how to configure the BGP proxy prefix SID feature for the segment-routing mapping client.
RP/0/RSP0/CPU0:router(config)# router bgp 1
RP/0/RSP0/CPU0:router(config-bgp)# address-family ip4 unicast
RP/0/RSP0/CPU0:router(config-bgp-af)# segment-routing prefix-sid-map
Verification
These examples show how to verify the BGP proxy prefix SID feature.
RP/0/RSP0/CPU0:router# show segment-routing mapping-server prefix-sid-map ipv4 detail
Prefix
1.1.1.1/32
SID Index: 10
Range: 200
Last Prefix: 1.1.1.200/32
Last SID Index: 209
Flags:
Number of mapping entries: 1
RP/0/RSP0/CPU0:router# show bgp ipv4 labeled-unicast 192.168.64.1/32
BGP routing table entry for 192.168.64.1/32
Versions:
Process bRIB/RIB SendTblVer
Speaker 117 117
Local Label: 16400
Last Modified: Oct 25 01:02:28.562 for 00:11:45Paths: (2 available, best #1)
Advertised to peers (in unique update groups):
201.1.1.1
Path #1: Received by speaker 0 Advertised to peers (in unique update groups):
201.1.1.1
Local
20.0.101.1 from 20.0.101.1 (20.0.101.1) Received Label 61
Origin IGP, localpref 100, valid, internal, best, group-best, multipath, labeled-unicast
Received Path ID 0, Local Path ID 0, version 117
Prefix SID Attribute Size: 7
Label Index: 1
RP/0/RSP0/CPU0:router# show route ipv4 unicast 192.68.64.1/32 detail
Routing entry for 192.168.64.1/32
Known via "bgp 65000", distance 200, metric 0, [ei]-bgp, labeled SR, type internal
Installed Oct 25 01:02:28.583 for 00:20:09
Routing Descriptor Blocks
20.0.101.1, from 20.0.101.1, BGP multi path
Route metric is 0
Label: 0x3d (61)
Tunnel ID: None
Binding Label: None
Extended communities count: 0
NHID:0x0(Ref:0)
Route version is 0x6 (6)
Local Label: 0x3e81 (16400)
IP Precedence: Not Set
QoS Group ID: Not Set
Flow-tag: Not Set
Fwd-class: Not Set
Route Priority: RIB_PRIORITY_RECURSIVE (12) SVD Type RIB_SVD_TYPE_LOCAL
Download Priority 4, Download Version 242
No advertising protos.
RP/0/RSP0/CPU0:router# show cef ipv4 192.168.64.1/32 detail
192.168.64.1/32, version 476, labeled SR, drop adjacency, internal 0x5000001 0x80 (ptr 0x71c42b40) [1], 0x0 (0x71c11590), 0x808 (0x722b91e0)
Updated Oct 31 23:23:48.733
Prefix Len 32, traffic index 0, precedence n/a, priority 4
Extensions: context-label:16400
gateway array (0x71ae7e78) reference count 3, flags 0x7a, source rib (7), 0 backups
[2 type 5 flags 0x88401 (0x722eb450) ext 0x0 (0x0)]
LW-LDI[type=5, refc=3, ptr=0x71c11590, sh-ldi=0x722eb450]
gateway array update type-time 3 Oct 31 23:49:11.720
LDI Update time Oct 31 23:23:48.733
LW-LDI-TS Oct 31 23:23:48.733
via 20.0.101.1/32, 0 dependencies, recursive, bgp-ext [flags 0x6020]
path-idx 0 NHID 0x0 [0x7129a294 0x0]
recursion-via-/32
unresolved
local label 16400
labels imposed {ExpNullv6}
RP/0/RSP0/CPU0:router# show bgp labels
BGP router identifier 2.1.1.1, local AS number 65000
BGP generic scan interval 60 secs
Non-stop routing is enabled
BGP table state: Active
Table ID: 0xe0000000 RD version: 245
BGP main routing table version 245
BGP NSR Initial initsync version 16 (Reached)
BGP NSR/ISSU Sync-Group versions 245/0
BGP scan interval 60 secs
Status codes: s suppressed, d damped, h history, * valid, > best
i - internal, r RIB-failure, S stale, N Nexthop-discard
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Rcvd Label Local Label
*>i1.1.1.1/32 1.1.1.1 3 16010
*> 2.1.1.1/32 0.0.0.0 nolabel 3
*> 192.68.64.1/32 20.0.101.1 2 16400
*> 192.68.64.2/32 20.0.101.1 2 16401
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