Cannot verify MPLS forwarding

[steven.crutchley]

Hi everyone, 

I'm trying to verify that label forwarding is taking place without having to revert to a PCAP.

The device I'm looking at is an ASBR in an interAS Option B setup. It is receiving a VPNv4 prefix from it's eBGP neighbor, installing a local label (with retain route-target all under the vpnv4 AFI) and then advertising it on to its VPNv4 Router Reflector. Everything is behaving as normal and the Option B session is working correctly. Hosts in the relevant VRFs can communicate ok. But I would expect the following output to show more than zero bytes switched:

RP/0/RP0/CPU0:ISP2-ASBR1#sh bgp vpnv4 unicast rd 100:1 172.20.10.1/32 | inc Label
Sat Feb 15 18:46:08.759 UTC
    Local Label: 24015
      Received Label 25015 
      Received Label 24023 
RP/0/RP0/CPU0:ISP2-ASBR1#show mpls forwarding labels 24015 detail
Sat Feb 15 18:46:11.840 UTC
Local  Outgoing    Prefix             Outgoing     Next Hop        Bytes       
Label  Label       or ID              Interface                    Switched    
------ ----------- ------------------ ------------ --------------- ------------
24015  24023       100:1:172.20.10.1/32   \
                                      Gi0/0/0/2    10.1.1.1        0           
     Updated: Feb 15 16:57:28.693
     Path Flags: 0x6000 [  ]
     Version: 948, Priority: 4
     Label Stack (Top -> Bottom): { 24023 }
     NHID: 0x0, Encap-ID: N/A, Path idx: 0, Backup path idx: 0, Weight: 0
     MAC/Encaps: 4/8, MTU: 1500
     Outgoing Interface: GigabitEthernet0/0/0/2 (ifhandle 0x01000040)
     Packets Switched: 0

RP/0/RP0/CPU0:ISP2-ASBR1#

Gi0/0/0/2 is the interface connecting to ISP1, so I'd expect to see the bytes switch to increment if I ping 172.20.10.1 from a host in the relevant VRF in ISP2. And indeed I can verify this with a PCAP with 24023 as the only label. So I know the packets are there. But the LFIB remains 0 no matter how much I send pings across the link. The interface counters on Gi0/0/0/2 increment (not shown here but I can get the output if you want) but not the LFIB counters.

Is this a limitation of working with virtual devices or is there some command I need to enter to enable this? 

More importantly, if this method won't work, does anyone know how I can verify labelled packets are being sent on a virtual IOS-XR without needing to PCAP?

[M02@rt37]

Hello @steven.crutchley 

Please share this output:

show mpls forwarding summary

[Harold Ritter]

Hi @steven.crutchley ,

What XRv9k version are you running?

I have seen older versions where only the counter for the lfib entry installed by the static route (10.1.1.1/32) between the ASBRs would get incremented instead of both the counter for the static route and the counter for BGP route (recursing via the static route). Can you check if the counter for the static route gets incremented when you ping the vrf route.

(on ISP2-ASBR1)

show mpls forwarding | i Gi0/0/0/2

Regards,