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ospf dr and load balancing

there are 5 routers on the lan, two of them have wan links(bandwidth is same),

one router is elected ospf dr router(has wan link),another router(has wan link) is not dr and bdr.

if there are networks whose cost to two routers are same, will another 3 routers choose two routers as next hop for load balancing ,or will they only choose dr routers as next hop?

2 REPLIES

Re: ospf dr and load balancing

DR/BDR won't affect your routing decisions (they have other functions). You can configure the other 3 to load balance (if you set the cost of both routes as equal) between the 2 WAN routers or to only send to one. Cisco routers will load-balance over a maximum of four equal-cost paths between a source and destination using either per-destination (default) or per-packet load balancing when using OSPF.

New Member

Re: ospf dr and load balancing

The OSPF DR (Designated Router) or BDR (Backup DR) doesn't have anything to do with the route selection.

The concept of the DR is introduced to avoid all routers on a shared segment from having to form adjacency with all other routers on the segment.

Instead all routers on the segment form an adjacency with the (B)DR.

The DR originates the LSA for the segment and ensures reliable updates of the other routers.

If your two WAN routers have equal cost paths to the same destinations, then the routers on the segment will load share over these paths.

http://www.cisco.com/warp/customer/104/1.html provides very could insight into OSPF.

http://www.cisco.com/warp/customer/105/46.html talks about load balancing and provides additional links.

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