CEF problem - Traffic forwarding

Mohamed Kamal mkamal at noor.net
Wed Sep 10 18:41:29 UTC 2014


Hello, 

I have a very strange problem on my ASR-1006 BRAS router. 

This router is having two equal paths toward a P router via IS-IS. The BRAS is seeing the P router over the two paths and the two paths are installed in the RIB and FIB as follows:

bng.rams.ca.asr1#sh ip cef 10.10.10.141 internal 

10.10.10.141/32, epoch 3, RIB[I], refcount 6, per-longest-match-prefix sharing
  sources: RIB, LTE 
  feature space:
   IPRM: 0x00028000
   Broker: linked, distributed at 1st priority
   LFD: 10.10.10.141/32 1 local label
   local label info: global/592
        contains path extension list
        disposition chain 0x7FCE5CB8C440
        label switch chain 0x7FCE5CB82FC0
  ifnums:
   GigabitEthernet0/0/0(8): 172.17.11.9
   GigabitEthernet1/0/0(24): 172.17.11.17
  path 7FCE67248388, path list 7FCE5FF51A40, share 1/1, type attached nexthop, for IPv4
    MPLS short path extensions: MOI flags = 0x0 label implicit-null
  nexthop 172.17.11.9 GigabitEthernet0/0/0, adjacency IP adj out of GigabitEthernet0/0/0, addr 172.17.11.9 7FCE5C406958
  path 7FCE6724B5B8, path list 7FCE5FF51A40, share 1/1, type attached nexthop, for IPv4
    MPLS short path extensions: MOI flags = 0x0 label implicit-null
  nexthop 172.17.11.17 GigabitEthernet1/0/0, adjacency IP adj out of GigabitEthernet1/0/0, addr 172.17.11.17 7FCE5079A540
  output chain: IP adj out of GigabitEthernet0/0/0, addr 172.17.11.9 7FCE5C406958

The problem is, CEF is seeing the two paths equal, but the output chain is only having one exit interface and the traffic is traversing this interface only!

This is the interface config:

bng.rams.ca.asr1#sh run all | sec 0/0/0
interface GigabitEthernet0/0/0
 description "Connected to p1 router"
 mtu 1600
 ip address 172.17.11.10 255.255.255.252
 ip redirects
 ip unreachables
 ip proxy-arp
 ip mtu 1600
 no ip load-sharing per-longest-match-prefix
 ip cef accounting non-recursive internal
 ip router isis
 ip flow monitor adsl input
 ip flow monitor adsl output
 ip pim dr-priority 1
 ip pim query-interval 30
 ip mfib forwarding input
 ip mfib forwarding output
 ip mfib cef input
 ip mfib cef output
 ip route-cache cef
 ip route-cache
 ip split-horizon
 ip igmp last-member-query-interval 1000
 ip igmp last-member-query-count 2
 ip igmp query-max-response-time 10
 ip igmp version 2
 ip igmp query-interval 60
 ip igmp tcn query count 2
 ip igmp tcn query interval 10

interface GigabitEthernet1/0/0
 description " Connected to p1 router"
 mtu 1600
 ip address 172.17.11.18 255.255.255.252
 ip redirects
 ip unreachables
 ip proxy-arp
 ip mtu 1600
 no ip load-sharing per-longest-match-prefix
 ip cef accounting non-recursive internal
 ip router isis
 ip flow monitor adsl input
 ip flow monitor adsl output
 ip pim dr-priority 1
 ip pim query-interval 30
 ip mfib forwarding input
 ip mfib forwarding output
 ip mfib cef input
 ip mfib cef output
 ip route-cache cef
 ip route-cache
 ip split-horizon
 ip igmp last-member-query-interval 1000
 ip igmp last-member-query-count 2
 ip igmp query-max-response-time 10
 ip igmp version 2
 ip igmp query-interval 60
 ip igmp tcn query count 2
 ip igmp tcn query interval 10

So, what do you think?

Regards,
Mohamed Kamal


More information about the NANOG mailing list