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nihammimm
Beginner

Asymmetric Routing issue

Hi,

One of the server hosted at Site-A , not able to connect the application which is hosted at Site-B Server , there is no firewall in between.Server IP's are pingable from both the end. See the below trace route from SITE-A to SITE-B and vice versa. based on below trace result we can see that there is some asymmetric route beween these two sites.

Does asymmetric routing can affect application operation?

Please advise ?


Core-SWITCH-SITE-A#traceroute 50.35.3.220 (Server-a)


  1 162.28.0.9    4 msec 0 msec 0 msec
  2 50.133.51.176 4 msec 0 msec 4 msec
  3 50.133.51.25 44 msec 48 msec 44 msec
  4 50.129.2.246   48 msec 48 msec 48 msec
  5 191.168.201.30 144 msec 140 msec 144 msec
  6 50.35.3.220    140 msec 140 msec 144 msec


Core-SWITCH-SITE-B#traceroute 162.18.17.28 (Server-b)

  1 50.135.2.3     152 msec 152 msec 156 msec
  2 50.133.51.22  136 msec 136 msec 140 msec
  3 50.133.50.2   136 msec 156 msec 144 msec
  4 50.133.251.175 140 msec 140 msec 140 msec
  5 162.28.0.8    140 msec 144 msec 140 msec
  6 162.28.17.28   148 msec 156 msec 152 msec

Regard,

1 REPLY 1
Chaitra Shree
Cisco Employee

Hi Niham,

Asymmetric routing occurs when transmit and receive  packets follow different paths between a host and the peer with which it  communicates. In your scenario, if you see a different path when you traceroute to server B from server A and vice versa, it indicates asymmetric routing .

Asymmetric routing can lead to issues like unicast flooding ,missing MLS entries, latency and drops. The below link provides a detailed explanation about asymmetric routing:

http://www.cisco.com/en/US/products/hw/switches/ps700/products_tech_note09186a00801d0808.shtml#cause1

This can be tackled by applying the following:

  • Adjust the MAC aging time on the respective switches to 14,400  seconds (four hours) or longer :

         mac-address-table aging-time seconds  [vlan vlan_id]

  • Change the ARP timeout on the routers to five minutes (300 seconds).
  • Change the MAC aging time and ARP timeout to the same timeout value.

HTH,

Chaitra