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Network connectivity or latency reported icmp redirect

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TitleNetwork connectivity or latency reported icmp redirect
Symptoms
  • Network latency
  • Slow ping response to/from servers
  • Application connection timeouts across router
  • Router CPU spike during backup or file transfer
Environment
  • S-series
  • N-series
  • Routing
  • Traffic latency
  • Slow ping response to and from servers
  • ICMP redirects condition.  Client default gateway is not optimal. 
Cause
  • Traffic is getting redirected from the router interface
  • Client ignores icmp redirect instruction
  • ICMP redirect traffic is soft-forwarded and rate limited on the S-series
  • To see icmp redirect packets being sent from router to traffic source to identify this condition, take a wireshark packet capture
Switch counters diagnostic procedure:
  1. config-> debug packet show-statistics <view cumulative stats>
  2. config -> debug packet clear-statistics <Clear these counters>
  3. allow time interval. ex: 10 seconds, 30 seconds - followed by
  4. config -> debug counters show-statistics

New stats output includes delta interval label (10, 30 secs etc) and fresh counters

S-Series(su-config)->debug packet show-statistics

                 Global Router Statistics - last cleared 12s ago
                      (repeat command to refresh counters)
--------------------------------------------------------------------------------
   type                                              count     hi-count-blade
--------------------------------------------------------------------------------
                                 Packet Counts
   Total Packets in:                                    670                  2
   IPv4 Packets in:                                     670                  2
   Non-Unicast Packets in:                           1                   2

    /clipped output/
    
Redirected:                                          367                  2

 
Resolution
Disable ICMP redirect on the associated interface.  This will be the default gateway interface of the traffic source.

 S-Series(su-config)->int vlan.0.1
 S-Series(su-config-intf-vlan.0.1)->no ip redirects 
 S-Series(su-config-intf-vlan.0.1)->exit
 S-Series(su-config)->


 
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