[BGP] vtysh commands following "ip nht resolve-via-default" are failing to apply

[vivekrnv]

• This is seen on 202411 and master
• Reproduced when docker_routing_config_mode is set to split mode
• Load any example config with the following pattern i.e.

ipv6 neighbor activate are run after the following command
ip nht resolve-via-default

!
password zebra
enable password zebra
!
ipv6 route fc00:1::/64 Loopback0
!
router bgp 65100
 bgp router-id 10.1.0.32
 bgp suppress-fib-pending
 bgp log-neighbor-changes
 no bgp ebgp-requires-policy
 no bgp default ipv4-unicast
 bgp bestpath as-path multipath-relax
 neighbor PEER_V4 peer-group
 neighbor PEER_V6 peer-group
 neighbor 10.0.0.1 remote-as 65200
 neighbor 10.0.0.1 peer-group PEER_V4
 neighbor 10.0.0.1 description ARISTA01T2
 neighbor 10.0.0.1 timers 3 10
 neighbor 10.0.0.1 timers connect 10
 neighbor 10.0.0.5 remote-as 65200
 neighbor 10.0.0.5 peer-group PEER_V4
 neighbor 10.0.0.5 description ARISTA03T2
 neighbor 10.0.0.5 timers 3 10
 neighbor 10.0.0.5 timers connect 10

 neighbor fc00::2 remote-as 65200
 neighbor fc00::2 peer-group PEER_V6
 neighbor fc00::2 description ARISTA01T2
 neighbor fc00::2 timers 3 10
 neighbor fc00::2 timers connect 10
 neighbor fc00::6 remote-as 65200
 neighbor fc00::6 peer-group PEER_V6
 neighbor fc00::6 description ARISTA03T2
 neighbor fc00::6 timers 3 10
 neighbor fc00::6 timers connect 10
 neighbor fc00::a remote-as 65200
 neighbor fc00::a peer-group PEER_V6
 neighbor fc00::a description ARISTA05T2
 neighbor fc00::a timers 3 10
 neighbor fc00::a timers connect 10
 !
address-family ipv4 unicast
  network 10.1.0.32/32
  neighbor 10.0.0.1 activate
  neighbor 10.0.0.5 activate
  neighbor 10.0.0.9 activate 
 exit-address-family
exit
!
ip nht resolve-via-default
!
ipv6 nht resolve-via-default
!
address-family ipv6 unicast
  network fc00:1::/64
  neighbor fc00::2 activate
  neighbor fc00::6 activate
  neighbor fc00::a activate
  neighbor fc00::e activate
 exit-address-family
exit
!

• sessions are established for ipv4 peers and not with ipv6 peers

show ip bgp summary

IPv4 Unicast Summary:
BGP router identifier 10.1.0.32, local AS number 65100 vrf-id 0
BGP table version 6427
RIB entries 12851, using 1644928 bytes of memory
Peers 24, using 494208 KiB of memory
Peer groups 2, using 128 bytes of memory


Neighbhor      V     AS    MsgRcvd    MsgSent    TblVer    InQ    OutQ  Up/Down      State/PfxRcd  NeighborName
-----------  ---  -----  ---------  ---------  --------  -----  ------  ---------  --------------  --------------
10.0.0.1       4  65200       3211       3232      6427      0       0  00:01:04             6370  ARISTA01T2
10.0.0.5       4  65200       3211       3232      6427      0       0  00:01:04             6370  ARISTA03T2
10.0.0.9       4  65200       3211       3232      6427      0       0  00:01:04             6370  ARISTA05T2
10.0.0.13      4  65200       3211       3232      6427      0       0  00:01:04             6370  ARISTA07T2

Total number of neighbors 24

show ipv6 bgp summary

IPv6 Unicast Summary:
BGP router identifier 10.1.0.32, local AS number 65100 vrf-id 0
BGP table version 6427
RIB entries 0, using 0 bytes of memory
Peers 0, using 0 KiB of memory
Peer groups 0, using 0 bytes of memory


Neighbhor    V    AS    MsgRcvd    MsgSent    TblVer    InQ    OutQ    Up/Down    State/PfxRcd    NeighborName
-----------  ---  ----  ---------  ---------  --------  -----  ------  ---------  --------------  --------------

Total number of neighbors 0

• Following error is seen. Commands after ip nht resolve-via-default are failed.

[220|mgmtd] sending configuration
[221|zebra] sending configuration
[227|bgpd] sending configuration
[237|staticd] sending configuration
Waiting for children to finish applying config...
line 355: % Unknown command[4]:  address-family ipv6 unicast
line 356: % Unknown command[4]:   network fc00:1::/64
line 360: % Unknown command[4]:   neighbor fc00::2 activate
line 361: % Unknown command[4]:   neighbor fc00::6 activate
line 362: % Unknown command[4]:   neighbor fc00::a activate
line 363: % Unknown command[4]:   neighbor fc00::e activate
line 364: % Unknown command[4]:   neighbor fc00::42 activate
line 365: % Unknown command[4]:   neighbor fc00::46 activate
line 366: % Unknown command[4]:   neighbor fc00::4a activate
line 367: % Unknown command[4]:   neighbor fc00::4e activate
line 368: % Unknown command[4]:   neighbor fc00::52 activate
line 369: % Unknown command[4]:   neighbor fc00::56 activate
line 370: % Unknown command[4]:   neighbor fc00::5a activate
line 371: % Unknown command[4]:   neighbor fc00::5e activate
line 372: % Unknown command[4]:   neighbor fc00::62 activate
line 373: % Unknown command[4]:   neighbor fc00::66 activate
line 374: % Unknown command[4]:   neighbor fc00::6a activate
line 375: % Unknown command[4]:   neighbor fc00::6e activate
line 376: % Unknown command[4]:   neighbor fc00::72 activate
line 377: % Unknown command[4]:   neighbor fc00::76 activate
line 378: % Unknown command[4]:   neighbor fc00::7a activate
line 379: % Unknown command[4]:   neighbor fc00::7e activate
line 380: % Unknown command[4]:   neighbor fc00::82 activate
line 381: % Unknown command[4]:   neighbor fc00::86 activate
line 382: % Unknown command[4]:   neighbor fc00::8a activate
line 383: % Unknown command[4]:   neighbor fc00::8e activate
line 384: % Unknown command[4]:  exit-address-family
line 385: Warning[4]...: early exit from config file

Potential suspect is this PR: https://github.com/sonic-net/sonic-buildimage/pull/20269/files#diff-8d9a6c3c705361c0b2105f78bc826617853ee00ed9208b6f241b4ad1587977ce

[vivekrnv]

@sudhanshukumar22 FYI

[dgsudharsan]

@adyeung @hasan-brcm @sudhanshukumar22 Can you please help prioritize this?