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Cisco Bug: CSCvt55408 - l3vpn 3 level ecmp:show cef exact-route not reliable for l3vpn prefix on encap PE

Last Modified

Jun 19, 2020

Products (1)

  • Cisco 8000 Series Routers

Known Affected Releases

7.2.1.BASE

Description (partial)

Symptom:
On Cisco 8000 series routers, "show cef exact-route" for a L3VPN prefix with BGP-LU will not display the exact path chosen.

This is a sample output generated in the Engineering lab
(and the IP addresses are samples)

500007 is the IGP label
200005 is the BGP-LU label
31034 is the VPN label

RP/0/RP0/CPU0:PE1-SF-F#show cef  vrf vpn1 136.1.2.202
Thu Mar 26 11:29:16.476 UTC
136.1.2.202/32, version 99635, internal 0x5000001 0x30 (ptr 0xd970ccbc) [1], 0x0 (0x0), 0x208 (0xa3aec6c0)
 Updated Mar 26 11:08:25.738
 Prefix Len 32, traffic index 0, precedence n/a, priority 3
   via 3.3.3.3/32, 2089 dependencies, recursive, bgp-multipath [flags 0x6080]
    path-idx 0 NHID 0x0 [0x9b308f40 0x0]
    recursion-via-/32
    next hop VRF - 'default', table - 0xe0000000
    next hop 3.3.3.3/32 via 100004/0/21
     next hop 100.15.3.5/32 Hu0/0/0/35.3 labels imposed {500007 200005 31034}
     next hop 100.15.4.5/32 Hu0/0/0/35.4 labels imposed {500007 200005 31034}
   via 4.4.4.4/32, 81 dependencies, recursive, bgp-multipath [flags 0x6080]
    path-idx 1 NHID 0x0 [0x9b309228 0x0]
    recursion-via-/32
    next hop VRF - 'default', table - 0xe0000000
    next hop 4.4.4.4/32 via 100005/0/21
     next hop 100.15.3.5/32 Hu0/0/0/35.3 labels imposed {500007 200009 400005}
     next hop 100.15.4.5/32 Hu0/0/0/35.4 labels imposed {500007 200009 400005}


RP/0/RP0/CPU0:PE1-SF-F#show cef vrf vpn1 exact-route 131.1.1.1  136.1.2.202 protocol icmp ingress-interface hu 0/0/0/0.1 location 0/RP0/CPU0
Tue Mar 24 17:31:02.281 UTC
136.1.2.192/28, version 20803, internal 0x5000001 0x30 (ptr 0xa0fb4dc0) [1], 0x0 (0x0), 0x208 (0xa2bdeb70)
Updated Mar 24 16:31:09.846 
 local adjacency 100.15.3.5
Prefix Len 28, traffic index 0, precedence n/a, priority 3
   via HundredGigE0/0/0/35.3
   via 3.3.3.3/32, 2089 dependencies, recursive, bgp-multipath [flags 0x6080]
    path-idx 0 NHID 0x0 [0x9b2e6038 0x0]
    recursion-via-/32
    next hop VRF - 'default', table - 0xe0000000
    next hop 3.3.3.3/32 via 100004/0/21
     next hop 100.15.3.5/32 Hu0/0/0/35.3 labels imposed {500007 200005 31067}

Based on the incoming packet, the actual path chosen by hardware is Hu0/0/0/35.4
However the path shown by the "show cef exact-route" CLI is Hu0/0/0/35.3

Conditions:
Cisco 8000 router is running IOS-XR release 7.2.1
BGP-LU is used in conjunction with L3VPN
L3VPN feature for Cisco 8000 is introduced in 7.2.1 XR release.
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