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Cisco Bug: CSCvi83457 - N7K: Post SSO next-hop adjacency is unresolved in UFIB causing CPU punt and intermittent drops

Last Modified

Jul 09, 2018

Products (1)

  • Cisco Nexus 7000 Series Switches

Known Affected Releases

6.2(14)

Description (partial)

Symptom:
Connectivity to remote subnet is experiencing drops.  
Next-Hop ARP and adjacency are resolved in the Sup but adjacency is unresolved at the module SW FIB level.

1) Identify the affected subnet. Example: 0.0.0.0/0
 
2) Check if the route present in the software.
 
show routing vrf all  0.0.0.0/0 detail
 
0.0.0.0/0, ubest/mbest: 1/0
    *via 10.104.96.237, [1/0], 03:27:10, static
         recursive next hop: 10.104.96.237/32  --> Next-hop to reach the subnet is 10.104.96.237
 
2b) Check if the ARP and Adjacency is present for the Next-Hop (or Recursive NH if present) in software
 
show ip arp 10.104.96.237 vrf all
IP ARP Table for all contexts
Total number of entries: 1
Address         Age       MAC Address     Interface
10.104.96.237   00:17:42  18ef.63e6.a7c2  Vlan125       --> ARP entry is present (in software) for NH in step #1
 
show ip adjacency 10.104.96.237 vrf all 
Address           MAC Address      Pref  Source     Interface
10.104.96.237    18ef.63e6.a7c2     50    arp        Vlan125  --> Adjacency is present (in software) for NH in step #1
 
 
3) Check if the next-hop is programmed in the line card 'software' (check all linecards)
 
show forwarding vrf all adjacency 10.104.96.237
 
slot  1
=======
IPv4 adjacency information
next-hop         rewrite info    interface 
-------------- --------------- -------------
10.104.96.237    unresolved   Vlan125       <<<<< if   "unresolved",   you are susceptible to this issue, but still check what LC hardware is programmed with below
 
slot  2
=======
IPv4 adjacency information
next-hop         rewrite info    interface 
-------------- --------------- -------------
10.104.96.237    unresolved   Vlan125
 

3b) Check if the next-hop is programmed in the line card 'hardware' (check all linecards)
 
show forwarding vrf all adjacency platform | be 10.104.96.237
next_hop:10.104.96.237  rewrite_info:unresolved   interface:Vlan125          -----> If  "unresolved"  and then above unresolved info   was pushed to hardware and likely causing packet drop.
HH:0xa028  Refcount:3  Flags:0x8080  Holder:0x0  pbr_cnt:0   wccp_cnt:0

Conditions:
hardware ip glean throttle is not configured.
issue occurs following a Sup Switchover
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