Balance OSPF and BGP

Unanswered Question
Feb 27th, 2007

Hi !

I have the follow situation, a router 2811 running a process of BGP (2 neighbor) and OSPF. My problem is balancing a subnet that the router receives in both processes. As we can see commandas above, we can observe that the routes were manipulated to have the same distance and metric, but the router only puts on the route-table the paths via BGP. What are the others mterics to router chosse de best path ??

### A subnet only in OSPF - distance 20 - metric 1 ####

ROUTER#sh ip route 10.5.60.0

Routing entry for 10.5.60.0/24

Known via "ospf 100", distance 20, metric 1

Tag 1, type extern 1

Last update from 10.5.2.10 on FastEthernet0/0, 02:04:27 ago

Routing Descriptor Blocks:

* 10.5.2.10, from 10.5.2.10, 02:04:27 ago, via FastEthernet0/0

Route metric is 1, traffic share count is 1

Route tag 1

### A subnet in OSPF and BGP, but only the BGPs mount ###

ROUTER#sh ip route 129.1.8.0

Routing entry for 129.1.8.0/24

Known via "bgp 65181", distance 20, metric 1

Tag 4230, type external

Last update from 172.31.2.22 02:06:51 ago

Routing Descriptor Blocks:

* 200.245.251.17, from 200.245.251.17, 02:06:51 ago

Route metric is 1, traffic share count is 1

AS Hops 2

Route tag 4230

172.31.2.22, from 172.31.2.22, 02:06:51 ago

Route metric is 1, traffic share count is 1

AS Hops 2

Route tag 4230

I have this problem too.
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carenas123 Mon, 03/05/2007 - 10:55

BGP could possibly receive multiple advertisements for the same route from multiple sources. BGP selects only one path as the best path. When the path is selected, BGP puts the selected path in the IP routing table and propagates the path to its neighbors. BGP uses the following criteria, in the order presented, to select a path for a destination:

?If the path specifies a next hop that is inaccessible, drop the update.

?Prefer the path with the largest weight.

?If the weights are the same, prefer the path with the largest local preference.

?If the local preferences are the same, prefer the path that was originated by BGP running on this router.

?If no route was originated, prefer the route that has the shortest AS_path.

?If all paths have the same AS_path length, prefer the path with the lowest origin type (where IGP is lower than EGP, and EGP is lower than incomplete).

?If the origin codes are the same, prefer the path with the lowest MED attribute.

?If the paths have the same MED, prefer the external path over the internal path.

?If the paths are still the same, prefer the path through the closest IGP neighbor.

?Prefer the path with the lowest IP address, as specified by the BGP router ID.

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