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OSPF load balancing on default route

Posted on 2013-06-05
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Last Modified: 2014-04-07
I have three routers. Router A gets a default route from Router B and Router C. But I would like to verify if ospf load balancing is working on the default route. I been monitoring the network traffic and noticed 95% of network traffic from Router A is going through Router B.

Below are some of the show commands I did on router A

Routing entry for 0.0.0.0/0, supernet
  Known via "ospf 100", distance 110, metric 1, candidate default path
  Tag 100, type extern 2, forward metric 1
  Last update from 192.168.239.29 on Vlan798, 03:18:21 ago
  Routing Descriptor Blocks:
  * 192.168.239.29, from 192.168.239.254, 03:18:21 ago, via Vlan798
      Route metric is 1, traffic share count is 1
      Route tag 100
    192.168.239.25, from 192.168.239.253, 03:18:21 ago, via Vlan799
      Route metric is 1, traffic share count is 1
      Route tag 100


-----------------------------------------------------------------------------
Router#sh ip cef 0.0.0.0
0.0.0.0/32
  receive



-------------------------------------------------------------------------------
Router#sh ip protocol
*** IP Routing is NSF aware ***

Routing Protocol is "ospf 100"
  Outgoing update filter list for all interfaces is not set
  Incoming update filter list for all interfaces is not set
  Router ID 192.168.239.250
  It is an autonomous system boundary router
  Redistributing External Routes from,
    connected, includes subnets in redistribution
    static, includes subnets in redistribution
  Number of areas in this router is 1. 1 normal 0 stub 0 nssa
  Maximum path: 4
  Routing for Networks:
    192.168.239.24 0.0.0.3 area 0
    192.168.239.28 0.0.0.3 area 0
  Routing Information Sources:
    Gateway         Distance      Last Update
    192.168.239.251         110      03:19:07
    192.168.239.254         110      03:19:07
    192.168.239.252         110      03:19:07
    192.168.239.253         110      03:19:07
  Distance: (default is 110)



--------------------------------------------------------------------------------
Router#sh ip cef 0.0.0.0 internal
0.0.0.0/32, epoch 4, flags receive, refcount 6, per-destination sharing
  sources: Spc
  feature space:
   Broker: linked
  subblocks:
   Special source: receive
  ifnums: (none)
  path 47CB8398, path list 47CB2B50, share 1/1, type receive, for IPv4
  receive
  output chain: receive
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Question by:ShadowColossus
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LVL 11

Expert Comment

by:naderz
ID: 39224101
Do you have the "show ip route" results?
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Author Comment

by:ShadowColossus
ID: 39224185
Sorry,

The output is below is the output for show ip route 0.0.0.0.

Routing entry for 0.0.0.0/0, supernet
  Known via "ospf 100", distance 110, metric 1, candidate default path
  Tag 100, type extern 2, forward metric 1
  Last update from 192.168.239.29 on Vlan798, 03:18:21 ago
  Routing Descriptor Blocks:
  * 192.168.239.29, from 192.168.239.254, 03:18:21 ago, via Vlan798
      Route metric is 1, traffic share count is 1
      Route tag 100
    192.168.239.25, from 192.168.239.253, 03:18:21 ago, via Vlan799
      Route metric is 1, traffic share count is 1
      Route tag 100
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LVL 11

Expert Comment

by:naderz
ID: 39224424
you do have both routes in the table as expected. you also have cef; which is actually handling the load-balancing on a per destination basis. so, it is possible that one destination may have many sources from inside and that could put all traffic on one route. one such destination could be e.g. Facebook.

you can experiment with fine tuning cef. let me know if you are interested.
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LVL 7

Expert Comment

by:Phyo HTET AUNG
ID: 39224427
cef default load balancing is per-destination which source-destination address pair. How many source network do you have in RouterA in this case?
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Accepted Solution

by:
naderz earned 200 total points
ID: 39226635
you can experiment with:

ip cef load-sharing algorithm include-ports source destination
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