04-25-2008 10:01 AM - edited 03-05-2019 10:37 PM
Folks,
I have a stub area with ABRs generating a default route into the ospf stub area, my question is that how will the routers react when they see 2 default routes with the same cost, will they load balance?
04-25-2008 10:45 AM
yes, by default OSPF does equal cost loadbalancing for up to six routes.
serg
04-26-2008 07:22 AM
Serg,
We have 2 default routes here, also I remember reading that the stub router chooses only 1 default route to go out of the stub area.
Please help anyone?
Parwal
04-26-2008 08:32 AM
Parwal,
Load-balancing will take place only if the cost to both ABRs is the same. You can determine the cost to each ABR using the following command:
show ip ospf border-routers
Regards,
04-26-2008 05:28 PM
Parwal, If you do not want to see 2 default routes in your stub area, use
area <> default-cost <>
command on your ABR to inject default route with higher cost.
serg
04-27-2008 04:24 AM
I have never seeen a router do loadbalancing between 2 default routes, so I asked, I am still not convinced, I remember reading somewhere that the routers in the stub network only use one abr to exit no matter what, I am simple not convinced.
Thanks
04-27-2008 05:29 AM
Parwal,
As I mentionned above, the router will load balance on the default received from the ABRs as long as the costs to these ABRs are the same.
r2#sh ip ospf border-routers
OSPF Process 1 internal Routing Table
Codes: i - Intra-area route, I - Inter-area route
i 1.1.1.1 [10] via 192.168.12.1, Ethernet0/0, ABR, Area 1, SPF 3
i 3.3.3.3 [10] via 192.168.23.3, Ethernet1/0, ABR, Area 1, SPF 3
r2#sh ip ro 0.0.0.0
Routing entry for 0.0.0.0/0, supernet
Known via "ospf 1", distance 110, metric 11, candidate default path, type inter area
Last update from 192.168.23.3 on Ethernet1/0, 00:00:17 ago
Routing Descriptor Blocks:
* 192.168.12.1, from 1.1.1.1, 00:00:17 ago, via Ethernet0/0
Route metric is 11, traffic share count is 1
192.168.23.3, from 3.3.3.3, 00:00:17 ago, via Ethernet1/0
Route metric is 11, traffic share count is 1
r2#
Regards,
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