[bgp] neighbor send-label won't generate labels

[Ziga M]

I'm trying to understand 'send-label' under bgp neighbor command and after a few hours I beleive I understand how it works, but I'm unable to produce the desired behaviour. I was trying on c7200 in gns3 and in csr1000v.

Topology is 3routers csr1---csr2---csr3. I have OSPF+LDP between R1 and R2 and BGP between R2 and R3. I see label for routes that R1 is generating on R2 (explicit-null) and I want to send these labels to R3:

R1 is advertising explicit-nul to R2 and R2 sees is properly.

csr2#show mpls forwarding
Local      Outgoing   Prefix           Bytes Label   Outgoing   Next Hop   
Label      Label      or Tunnel Id     Switched      interface             
17         explicit-n 10.0.0.1/32      0             Gi2        10.0.12.1   

csr2#show ip cef 10.0.0.1
10.0.0.1/32
  nexthop 10.0.12.1 GigabitEthernet2 label explicit-null

csr2#show ip ro      
O        10.0.0.1/32 [110/34] via 10.0.12.1, 01:31:15, GigabitEthernet2

But when I check if these labes are added into BGP, I see no-labels:

csr2#show ip bgp labels 
   Network          Next Hop      In label/Out label
   10.0.0.1/32      10.0.12.1       nolabel/nolabel

Show mpls forwarding reveals that csr2 generated label 17 for this network, but it's not advertising this over BGP to csr3. It's sending without label.

router bgp 10
 bgp log-neighbor-changes
 neighbor 10.0.0.3 remote-as 10
 neighbor 10.0.0.3 update-source Loopback0
 !
 address-family ipv4
  redistribute ospf 1 route-map REDIS
  neighbor 10.0.0.3 activate
  neighbor 10.0.0.3 next-hop-self
  neighbor 10.0.0.3 send-label explicit-null
 exit-address-family

csr2#show ip bgp neighbors 
BGP neighbor is 10.0.0.3,  remote AS 10, internal link
    ipv4 MPLS Label capability: advertised

I was testing in CSR1000V 15.4(2)S2 and in C7200 15.2(S3). What am I missing?

BR, Ziga

[Nagendra Kumar Nainar]

Hi Ziga,

You seems to have enabled this feature only on csr2 as below:

    ipv4 MPLS Label capability: advertised

By default the ipv4 prefixes will be advertised in AFI=1;SAFI=1. In order to advertise labels, we need AFI=1;SAFI=4. THis will be used only when it is enabled on both the sides (else the neighbor may not understand the update).

-Nagendra

[Ziga M]

Hi,

Thanks!! This was part of the problem, I added 'send-label' on the other side too, but still don't see labels. R2 in the middle is redistributing ospf to bgp and received 'explicit-null' to reach R1.

R2#show mpls fo
Local      Outgoing   Prefix           Bytes Label   Outgoing   Next Hop    
Label      Label      or Tunnel Id     Switched      interface              
17         explicit-n 10.0.0.1/32      0             Gi2        10.0.12.1   
18         No Label   10.0.0.3/32      0             Gi3        10.0.23.3   

R2#show ip bgp lab
   Network          Next Hop      In label/Out label
   10.0.0.1/32      10.0.12.1       nolabel/nolabel
   10.0.0.3/32      10.0.0.3        nolabel/imp-null
   10.0.12.0/24     0.0.0.0         imp-null/nolabel

R2#show ip bgp

     Network          Next Hop            Metric LocPrf Weight Path
 *>  10.0.0.1/32      10.0.12.1               34         32768 ?
 r>i 10.0.0.3/32      10.0.0.3                 0    100      0 i
 *>  10.0.12.0/24     0.0.0.0                  0         32768 ?

second problem that I'm observing is that r3 is advertising it's loopback IP=10.0.0.3 via BGP and ospf but it's not in use at R2 (RIB-failure) and therefor R2 is not sending it towards R1. R1 also needs to get label from R2 to reach R3. I need ospf between R2 and R3 in order to establish BGP over loopback IPs.

[yzamoram]

Hi,

Verify that your WAN interfaces have enabled this command:

"mpls bgp forwarding"

BR