[BGP LS] bgp_peer_segment missing in "gobgp global rib -a ls" for EBGP EPE LINK

[Ze-Pink]

Hi,

I would like to raise an issue that we found when we send BGP EPE labels to GoBGP via BGP-LS.

Architecture in place :

          (R1)<---[eBGP Labeled Unicast with EPE activated]--->(R2)
            |
            |
     eBGP Link-State 
            |
            |
         (GOBGP)

For your information R1 is a Nokia SROS router.

R1 has 2 BGP EPE labels applied for the eBGP session with R2 :

A:R1# show router bgp neighbor 172.16.210.0 epe-statistics 

Label               Type                Pkt Count           Byte Count
524285              node-sid            0                   0
524286              adj-sid             0                   0

R1 is advertising 6 BGP-LS routes to GoBGP :

• 4 routes related to the ISIS configuration (not relevant here)
• 2 routes related to the BGP EPE configuration (one for the node_sid label and the other one for the adjacency_sid label)

A:R1# show router bgp neighbor 10.204.1.2 bgp-ls advertised-routes 

 BGP Router ID:192.168.1.3      AS:5410        Local AS:5410       

 Legend -
 Status codes  : u - used, s - suppressed, h - history, d - decayed, * - valid
                 l - leaked, x - stale, > - best, b - backup, p - purge
 Origin codes  : i - IGP, e - EGP, ? - incomplete

BGP-LS NLRIs

Flag  Network                                            LocalPref   MED
      Nexthop (Router)                                   Path-Id     IGP Cost
      As-Path                                                        Label
i     ISIS Level-1/1522                                * n/a         None
      0.0.21.34/3232235779/--                                        
       0x192168001003                                                
i     ISIS Level-2/1522                                * n/a         None
      0.0.21.34/3232235779/--                                        
       0x192168001003                                                
i     BGP/0                                            * n/a         None
      0.0.21.34/0/-/192.168.1.3                                      
       -                                                             
      0.0.50.44/0/-/192.168.70.3                                     
       -                                                             
      -/-/-                                                          
       172.16.210.1/172.16.210.0                                     
       -                                                             
       -                                                             
i     BGP/0                                            * n/a         None
      0.0.21.34/0/-/192.168.1.3                                      
       -                                                             
      0.0.50.44/0/-/192.168.70.3                                     
       -                                                             
      -/4/0                                                          
       172.16.210.1/172.16.210.0                                     
       -                                                             
       -                                                             
i     ISIS Level-2/1522                                * n/a         None
      0.0.21.34/3232235779/--                                        
       0x192168001003                                                
      -/-                                                            
       192.168.1.103/32                                              
i     ISIS Level-2/1522                                * n/a         None
      0.0.21.34/3232235779/--                                        
       0x192168001003                                                
      -/-                                                            
       192.168.1.3/32                                                

Routes : 6

On GoBGP side, only 5 routes (instead of 6) are in the BGP LS global rib table :

gobgp_lab_te_mini:/# gobgp global rib -a ls 
   Network                                                                                             Next Hop             AS_PATH              Age        Attrs
*  NLRI { LINK { LOCAL_NODE: 192.168.1.3 REMOTE_NODE: 192.168.70.3 LINK: 172.16.210.1->172.16.210.0} } 192.168.1.3          5410                 00:00:25   [{Origin: i} {LsAttributes: {Peer Adjacency SID: 524286} }]
*  NLRI { NODE { AS:5410 BGP-LS ID:3232235779 1921.6800.1003 ISIS-L2:5410 } }                          192.168.1.3          5410                 00:00:25   [{Origin: i} {LsAttributes: {Node Flags: ****B***} {Node Name: BTR03_MINI} {ISIS Area ID: [73 0 1]} {Local RouterID IPv4: 192.168.1.3} {SR Capabilities: Flags:0 SRGB Ranges: 18432:118433 } {SR Algorithms: [0]} {Local RouterID IPv4: 192.168.1.3} }]
*  NLRI { NODE { AS:5410 BGP-LS ID:3232235779 1921.6800.1003 ISIS-L1:5410 } }                          192.168.1.3          5410                 00:00:25   [{Origin: i} {LsAttributes: {Node Flags: ****B***} {Node Name: BTR03_MINI} {ISIS Area ID: [73 0 1]} {Local RouterID IPv4: 192.168.1.3} {SR Capabilities: Flags:0 SRGB Ranges: 18432:118433 } {SR Algorithms: [0]} {Local RouterID IPv4: 192.168.1.3} }]
*  NLRI { PREFIXv4 { LOCAL_NODE: 1921.6800.1003 PREFIX: [192.168.1.103/32] } }                         192.168.1.3          5410                 00:00:25   [{Origin: i} {LsAttributes: {IGP Flags: ********} {Prefix opaque attribute: []} {Prefix SID: 11581} }]
*  NLRI { PREFIXv4 { LOCAL_NODE: 1921.6800.1003 PREFIX: [192.168.1.3/32] } }                           192.168.1.3          5410                 00:00:25   [{Origin: i} {LsAttributes: {IGP Flags: ********} {Prefix opaque attribute: []} {Prefix SID: 10581} }]

Here are GoBGP logs :

time=2026-01-11T11:01:17.529Z level=DEBUG msg="New connection for non admin-state-up peer" Topic=Peer Key=192.168.1.3 "Admin State"=adminStateDown
time=2026-01-11T11:01:17.618Z level=DEBUG msg="set admin state" Topic=Peer Key=192.168.1.3 Message="adminStateUp requested"
time=2026-01-11T11:01:17.618Z level=DEBUG msg="admin state changed" Topic=Peer Key=192.168.1.3 State=BGP_FSM_IDLE adminState=adminStateUp
time=2026-01-11T11:01:17.618Z level=INFO msg="Administrative start" Topic=Peer Key=192.168.1.3 State=BGP_FSM_IDLE
time=2026-01-11T11:01:22.622Z level=DEBUG msg="IdleHoldTimer expired" Topic=Peer Key=192.168.1.3 State=BGP_FSM_IDLE Duration=5
time=2026-01-11T11:01:22.622Z level=DEBUG msg="state changed" Topic=Peer Key=192.168.1.3 old=BGP_FSM_IDLE new=BGP_FSM_ACTIVE reason=idle-hold-timer-expired
time=2026-01-11T11:01:22.622Z level=INFO msg="starting outgoing connection manager" Topic=Peer Key=192.168.1.3
time=2026-01-11T11:01:24.230Z level=DEBUG msg="try to connect" Topic=Peer Key=192.168.1.3
time=2026-01-11T11:01:24.232Z level=DEBUG msg="outgoing connection established" Topic=Peer Key=192.168.1.3
time=2026-01-11T11:01:24.233Z level=DEBUG msg="open message received on outgoing connection" Topic=Peer Key=192.168.1.3 remote=192.168.1.3:179
time=2026-01-11T11:01:24.233Z level=DEBUG msg="state changed" Topic=Peer Key=192.168.1.3 old=BGP_FSM_ACTIVE new=BGP_FSM_OPENCONFIRM reason=open-msg-received
time=2026-01-11T11:01:24.238Z level=INFO msg="Peer Up" Topic=Peer Key=192.168.1.3
time=2026-01-11T11:01:24.238Z level=DEBUG msg="state changed" Topic=Peer Key=192.168.1.3 old=BGP_FSM_OPENCONFIRM new=BGP_FSM_ESTABLISHED reason=open-msg-negotiated
time=2026-01-11T11:01:52.532Z level=DEBUG msg="received update" Topic=Peer Key=192.168.1.3 nlri=[] withdrawals=[] path_attributes="[{MpReach(ls): {Nexthop: 192.168.1.3, NLRIs: [NLRI { LINK { LOCAL_NODE: 192.168.1.3 REMOTE_NODE: 192.168.70.3 LINK: 172.16.210.1->172.16.210.0} }:0]}} {Origin: i} {AsPath: 5410} {LsAttributes: {Peer Node SID: 524285} }]"
time=2026-01-11T11:01:52.532Z level=DEBUG msg="create Destination" Topic=Table Nlri="NLRI { LINK { LOCAL_NODE: 192.168.1.3 REMOTE_NODE: 192.168.70.3 LINK: 172.16.210.1->172.16.210.0} }"
time=2026-01-11T11:01:52.532Z level=DEBUG msg="create Destination" Topic=Table Nlri="NLRI { LINK { LOCAL_NODE: 192.168.1.3 REMOTE_NODE: 192.168.70.3 LINK: 172.16.210.1->172.16.210.0} }"
time=2026-01-11T11:01:52.532Z level=DEBUG msg="From me, ignore" Topic=Peer Key=192.168.1.3 Topic=Peer Key=192.168.1.3 Data="{ NLRI { LINK { LOCAL_NODE: 192.168.1.3 REMOTE_NODE: 192.168.70.3 LINK: 172.16.210.1->172.16.210.0} } | src: { 192.168.1.3 | as: 5410, id: 192.168.1.3 }, nh: 192.168.1.3 }"
time=2026-01-11T11:01:52.532Z level=DEBUG msg="received update" Topic=Peer Key=192.168.1.3 nlri=[] withdrawals=[] path_attributes="[{MpReach(ls): {Nexthop: 192.168.1.3, NLRIs: [NLRI { LINK { LOCAL_NODE: 192.168.1.3 REMOTE_NODE: 192.168.70.3 LINK: 172.16.210.1->172.16.210.0} }:0]}} {Origin: i} {AsPath: 5410} {LsAttributes: {Peer Adjacency SID: 524286} }]"
time=2026-01-11T11:01:52.532Z level=DEBUG msg="Implicit withdrawal of old path, since we have learned new path from the same peer" Topic=Table Key="NLRI { LINK { LOCAL_NODE: 192.168.1.3 REMOTE_NODE: 192.168.70.3 LINK: 172.16.210.1->172.16.210.0} }" Path="{ NLRI { LINK { LOCAL_NODE: 192.168.1.3 REMOTE_NODE: 192.168.70.3 LINK: 172.16.210.1->172.16.210.0} } | src: { 192.168.1.3 | as: 5410, id: 192.168.1.3 }, nh: 192.168.1.3 }"
time=2026-01-11T11:01:52.532Z level=DEBUG msg="From me, ignore" Topic=Peer Key=192.168.1.3 Topic=Peer Key=192.168.1.3 Data="{ NLRI { LINK { LOCAL_NODE: 192.168.1.3 REMOTE_NODE: 192.168.70.3 LINK: 172.16.210.1->172.16.210.0} } | src: { 192.168.1.3 | as: 5410, id: 192.168.1.3 }, nh: 192.168.1.3 }"
time=2026-01-11T11:01:52.532Z level=DEBUG msg="received update" Topic=Peer Key=192.168.1.3 nlri=[] withdrawals=[] path_attributes="[{MpReach(ls): {Nexthop: 192.168.1.3, NLRIs: [NLRI { NODE { AS:5410 BGP-LS ID:3232235779 1921.6800.1003 ISIS-L2:5410 } }:0 NLRI { NODE { AS:5410 BGP-LS ID:3232235779 1921.6800.1003 ISIS-L1:5410 } }:0]}} {Origin: i} {AsPath: 5410} {LsAttributes: {Node Flags: ****B***} {Node Name: BTR03_MINI} {ISIS Area ID: [73 0 1]} {Local RouterID IPv4: 192.168.1.3} {SR Capabilities: Flags:192 SRGB Ranges: 18432:118433 } {SR Algorithms: [0]} }]"
time=2026-01-11T11:01:52.532Z level=DEBUG msg="create Destination" Topic=Table Nlri="NLRI { NODE { AS:5410 BGP-LS ID:3232235779 1921.6800.1003 ISIS-L2:5410 } }"
time=2026-01-11T11:01:52.532Z level=DEBUG msg="create Destination" Topic=Table Nlri="NLRI { NODE { AS:5410 BGP-LS ID:3232235779 1921.6800.1003 ISIS-L1:5410 } }"
time=2026-01-11T11:01:52.532Z level=DEBUG msg="create Destination" Topic=Table Nlri="NLRI { NODE { AS:5410 BGP-LS ID:3232235779 1921.6800.1003 ISIS-L2:5410 } }"
time=2026-01-11T11:01:52.532Z level=DEBUG msg="From me, ignore" Topic=Peer Key=192.168.1.3 Topic=Peer Key=192.168.1.3 Data="{ NLRI { NODE { AS:5410 BGP-LS ID:3232235779 1921.6800.1003 ISIS-L2:5410 } } | src: { 192.168.1.3 | as: 5410, id: 192.168.1.3 }, nh: 192.168.1.3 }"
time=2026-01-11T11:01:52.532Z level=DEBUG msg="create Destination" Topic=Table Nlri="NLRI { NODE { AS:5410 BGP-LS ID:3232235779 1921.6800.1003 ISIS-L1:5410 } }"
time=2026-01-11T11:01:52.532Z level=DEBUG msg="From me, ignore" Topic=Peer Key=192.168.1.3 Topic=Peer Key=192.168.1.3 Data="{ NLRI { NODE { AS:5410 BGP-LS ID:3232235779 1921.6800.1003 ISIS-L1:5410 } } | src: { 192.168.1.3 | as: 5410, id: 192.168.1.3 }, nh: 192.168.1.3 }"
time=2026-01-11T11:01:52.532Z level=DEBUG msg="received update" Topic=Peer Key=192.168.1.3 nlri=[] withdrawals=[] path_attributes="[{MpReach(ls): {Nexthop: 192.168.1.3, NLRIs: [NLRI { PREFIXv4 { LOCAL_NODE: 1921.6800.1003 PREFIX: [192.168.1.103/32] } }:0]}} {Origin: i} {AsPath: 5410} {LsAttributes: {IGP Flags: ********} {Prefix SID: 11581} }]"
time=2026-01-11T11:01:52.532Z level=DEBUG msg="create Destination" Topic=Table Nlri="NLRI { PREFIXv4 { LOCAL_NODE: 1921.6800.1003 PREFIX: [192.168.1.103/32] } }"
time=2026-01-11T11:01:52.532Z level=DEBUG msg="create Destination" Topic=Table Nlri="NLRI { PREFIXv4 { LOCAL_NODE: 1921.6800.1003 PREFIX: [192.168.1.103/32] } }"
time=2026-01-11T11:01:52.532Z level=DEBUG msg="From me, ignore" Topic=Peer Key=192.168.1.3 Topic=Peer Key=192.168.1.3 Data="{ NLRI { PREFIXv4 { LOCAL_NODE: 1921.6800.1003 PREFIX: [192.168.1.103/32] } } | src: { 192.168.1.3 | as: 5410, id: 192.168.1.3 }, nh: 192.168.1.3 }"
time=2026-01-11T11:01:52.532Z level=DEBUG msg="received update" Topic=Peer Key=192.168.1.3 nlri=[] withdrawals=[] path_attributes="[{MpReach(ls): {Nexthop: 192.168.1.3, NLRIs: [NLRI { PREFIXv4 { LOCAL_NODE: 1921.6800.1003 PREFIX: [192.168.1.3/32] } }:0]}} {Origin: i} {AsPath: 5410} {LsAttributes: {IGP Flags: ********} {Prefix SID: 10581} }]"
time=2026-01-11T11:01:52.532Z level=DEBUG msg="create Destination" Topic=Table Nlri="NLRI { PREFIXv4 { LOCAL_NODE: 1921.6800.1003 PREFIX: [192.168.1.3/32] } }"
time=2026-01-11T11:01:52.532Z level=DEBUG msg="create Destination" Topic=Table Nlri="NLRI { PREFIXv4 { LOCAL_NODE: 1921.6800.1003 PREFIX: [192.168.1.3/32] } }"
time=2026-01-11T11:01:52.532Z level=DEBUG msg="From me, ignore" Topic=Peer Key=192.168.1.3 Topic=Peer Key=192.168.1.3 Data="{ NLRI { PREFIXv4 { LOCAL_NODE: 1921.6800.1003 PREFIX: [192.168.1.3/32] } } | src: { 192.168.1.3 | as: 5410, id: 192.168.1.3 }, nh: 192.168.1.3 }"

It seems that GoBGP is interpretating both BGP EPE LINK NLRIs as the same route and so it only keeps one EPE label (maybe the last update received).
As those routes have the same key, maybe that's why :
"NLRI { LINK { LOCAL_NODE: 192.168.1.3 REMOTE_NODE: 192.168.70.3 LINK: 172.16.210.1->172.16.210.0} }

Those 2 labels are important to keep inside GoBGP the global rib.

Thank you.

BR,

[fujita]

Where in any RFC does it state that EPE Link NLRIs with different labels must be treated as different NLRIs?

[Ze-Pink]

Thank you for your reply.
I add a Cisco IOS XR device that has the "same" role as GoBGP in order to compare the routes received.
So this device will receive the same routes as GoBGP sent by R1 router.

         (IOS XR)
            |
            |
      eBGP Link-State
            |
            |
          (R1)<---[eBGP Labeled Unicast with EPE activated]--->(R2)
            |
            |
     eBGP Link-State 
            |
            |
         (GOBGP)

As you can see, the cisco IOS XR receives 6 BGP-LS routes (the same number as R1 is sending) :

RP/0/RP0/CPU0:xrd1#show bgp link-state link-state 
Sun Jan 11 16:45:13.144 UTC
BGP router identifier 1.1.1.1, local AS number 12345
BGP generic scan interval 60 secs
Non-stop routing is enabled
BGP table state: Active
Table ID: 0x0   RD version: 7
BGP table nexthop route policy: 
BGP main routing table version 7
BGP NSR Initial initsync version 1 (Reached)
BGP NSR/ISSU Sync-Group versions 0/0
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
Prefix codes: E link, V node, T IP reachable route, S SRv6 SID, SP SRTE Policy, u/U unknown
              I Identifier, N local node, R remote node, L link, P prefix, S SID, C candidate path
              L1/L2 ISIS level-1/level-2, O OSPF, D direct, ST static/peer-node, SR Segment Routing
              a area-ID, l link-ID, t topology-ID, s ISO-ID,
              c confed-ID/ASN, b bgp-identifier, r router-ID, te te-router-ID, sd SID
              i if-address, n nbr-address, o OSPF Route-type, p IP-prefix
              d designated router address, po protocol-origin, f flag
              e endpoint-ip, cl color, as originator-asn oa originator-address
              di discriminator
   Network            Next Hop            Metric LocPrf Weight Path
*> [V][L1][I0x1522][N[c5410][b192.168.1.3][s1921.6800.1003.00]]/328
                      10.205.1.1                             0 5410 i
*> [V][L2][I0x1522][N[c5410][b192.168.1.3][s1921.6800.1003.00]]/328
                      10.205.1.1                             0 5410 i
*> [E][B][I0x0][N[c5410][b0.0.0.0][q192.168.1.3]][R[c12844][b0.0.0.0][q192.168.70.3]][L[l4.0][i172.16.210.1][n172.16.210.0]]/760
                      10.205.1.1                             0 5410 i
*> [E][B][I0x0][N[c5410][b0.0.0.0][q192.168.1.3]][R[c12844][b0.0.0.0][q192.168.70.3]][L[i172.16.210.1][n172.16.210.0]]/664
                      10.205.1.1                             0 5410 i
*> [T][L2][I0x1522][N[c5410][b192.168.1.3][s1921.6800.1003.00]][P[p192.168.1.3/32]]/400
                      10.205.1.1                             0 5410 i
*> [T][L2][I0x1522][N[c5410][b192.168.1.3][s1921.6800.1003.00]][P[p192.168.1.103/32]]/400
                      10.205.1.1                             0 5410 i

The BGP routes corresponding to EPE links are the following ones :

• Route for sending EPE Peer-Adj-SID :

RP/0/RP0/CPU0:xrd1#sh bgp link-state link-state [E][B][I0x0][N[c5410][b0.0.0.0][q192.168.1.3]][R[c12844][b0.0.0.0][q192.168.70.3]][L[l4.0][i172.16.210.1][n172.16.210.0]]/760 detail

Sun Jan 11 17:33:19.665 UTC
BGP routing table entry for [E][B][I0x0][N[c5410][b0.0.0.0][q192.168.1.3]][R[c12844][b0.0.0.0][q192.168.70.3]][L[l4.0][i172.16.210.1][n172.16.210.0]]/760
NLRI Type: Link
Protocol: BGP
Identifier: 0x0
Local Node Descriptor:
        AS Number: 5410
        BGP Identifier: 0.0.0.0
        BGP Router Identifier: 192.168.1.3
Remote Node Descriptor:
        AS Number: 12844
        BGP Identifier: 0.0.0.0
        BGP Router Identifier: 192.168.70.3
Link Descriptor:
        Link ID: 4.0
        Local Interface Address IPv4: 172.16.210.1
        Neighbor Interface Address IPv4: 172.16.210.0

Versions:
  Process           bRIB/RIB  SendTblVer
  Speaker                   4            4
    Flags: 0x00000001+0x00000000; 
Last Modified: Jan 11 16:40:36.969 for 00:52:42
Paths: (1 available, best #1)
  Not advertised to any peer
  Path #1: Received by speaker 0
  Flags: 0x2000000001068001+0x00, import: 0x020
  Not advertised to any peer
  5410, (received & used)
    10.205.1.1 from 10.205.1.1 (192.168.1.3), if-handle 0x00000000
      Origin IGP, localpref 100, valid, external, best, group-best
      Received Path ID 0, Local Path ID 1, version 4
      Link-state: Peer-Adj-SID: 524286 

• Route for sending EPE Peer-Node-SID :
  RP/0/RP0/CPU0:xrd1#sh bgp link-state link-state [E][B][I0x0][N[c5410][b0.0.0.0][q192.168.1.3]][R[c12844][b0.0.0.0][q192.168.70.3]][L[i172.16.210.1][n172.16.210.0]]/664 detail

Sun Jan 11 17:34:09.391 UTC
BGP routing table entry for [E][B][I0x0][N[c5410][b0.0.0.0][q192.168.1.3]][R[c12844][b0.0.0.0][q192.168.70.3]][L[i172.16.210.1][n172.16.210.0]]/664
NLRI Type: Link
Protocol: BGP
Identifier: 0x0
Local Node Descriptor:
        AS Number: 5410
        BGP Identifier: 0.0.0.0
        BGP Router Identifier: 192.168.1.3
Remote Node Descriptor:
        AS Number: 12844
        BGP Identifier: 0.0.0.0
        BGP Router Identifier: 192.168.70.3
Link Descriptor:
        Local Interface Address IPv4: 172.16.210.1
        Neighbor Interface Address IPv4: 172.16.210.0

Versions:
  Process           bRIB/RIB  SendTblVer
  Speaker                   5            5
    Flags: 0x00000001+0x00000000; 
Last Modified: Jan 11 16:40:36.969 for 00:53:32
Paths: (1 available, best #1)
  Not advertised to any peer
  Path #1: Received by speaker 0
  Flags: 0x2000000001068001+0x00, import: 0x020
  Not advertised to any peer
  5410, (received & used)
    10.205.1.1 from 10.205.1.1 (192.168.1.3), if-handle 0x00000000
      Origin IGP, localpref 100, valid, external, best, group-best
      Received Path ID 0, Local Path ID 1, version 5
      Link-state: Peer-SID: 524285 

As you can see, the NLRI routes are not identical because the Link Descriptor is different.

1. [E][B][I0x0][N[c5410][b0.0.0.0][q192.168.1.3]][R[c12844][b0.0.0.0][q192.168.70.3]][L[i172.16.210.1][n172.16.210.0]]/664
   Link Descriptor:
   Local Interface Address IPv4: 172.16.210.1
   Neighbor Interface Address IPv4: 172.16.210.0

2. [E][B][I0x0][N[c5410][b0.0.0.0][q192.168.1.3]][R[c12844][b0.0.0.0][q192.168.70.3]][L[l4.0][i172.16.210.1][n172.16.210.0]]/760
   Link Descriptor:
   Link ID: 4.0
   Local Interface Address IPv4: 172.16.210.1
   Neighbor Interface Address IPv4: 172.16.210.0

The second one is referencing the TLV 258 (Link ID 4.0) which is defined in RFC 9552.
As the NLRIs are not the same, they are considered as different routes on the router.

But on the RFC9552, I found this extract on chapter 5.2.2. Link Descriptors:
If interface and neighbor addresses, either IPv4 or IPv6, are
present, then the interface/neighbor address TLVs MUST be
included, and the Link Local/Remote Identifiers TLV MUST NOT be
included in the Link Descriptor. The Link Local/Remote
Identifiers TLV MAY be included in the link attribute when
available

I'm not sure if you follow that rule on GoBGP implementation for sending messages, but as I receiver, both nlri are different and should appear on the global rib.

What is your opinion?

Thank you