Solved: Re: ospf type 5 prefix and bgp

anastasiou82 · ‎07-01-2023

Hi everyone.

The last days i have been struggling with the following case:

Lets assume that we have two directly connected routers R1 ----> R2 . Among them there is eBGP Peering. R2 advertises some prefixes to R1 through BGP. Moreover on R1 i have configured some static routes as well as i have

redistributed

those routes into ospf

(redistribute static)

on R1. When the eBGP Peering is down, i am able to see the

redistributed

static routes as ospf type 5 (

show ip ospf

database summary). But, in case where eBGP peering is up, ospf type 5 routes are removed from ospf database.

Could someone explain me why this happens ?

Thanks a lot,

Nikos

Kanan Huseynli · ‎07-02-2023

Hi,

the reason is

redistribution

happens through routing table. If there is no route in routing table with

redistributing

protocol, then it can not be

redistributed

to another protocol.

In your case, you have static, ospf and BGP. You learn the same routes from BGP and static. When BGP is UP, routes installed to routing table as BGP route. Since you don't have BGP>OSPF

redistribution

you don't see any external

(redistributed)

route in OSPF (type5).

When BGP is down, BGP routes are gone from routing table and now for prefixes static routes are installed. You have

STATIC> OSPF

thus rotues are

redistributed

and you see type5 LSA for external prefixes.

HTH,
Please rate and mark as an accepted solution if you have found any of the information provided useful.

View solution in original post

MHM Cisco World · ‎07-01-2023

That not complete story R must ibgp with other router which make this issue

anastasiou82 · ‎07-01-2023

The static routes and the routes which are advertised over eBGP are the same.

Flavio Miranda · ‎07-01-2023

Hi

Do you have

redistribute

static on BGP ?

anastasiou82 · ‎07-01-2023

Hi,

Yes on R1. Essentially the static routes on R1 are advertised over eBGP from R2

Flavio Miranda · ‎07-01-2023

This can be due the protocol preference as router selects the route with the highest preference. eBGP preference is 255 while OSPF is 10.

when the BGP is down the OSPF routes is installed but when eBGP come up , it has the preference

anastasiou82 · ‎07-01-2023

Jul 1 16:33:18.246: RIB Redist, Topo Base, dest x.x.x.x, mask 255.255.224.0, Down

Flavio Miranda · ‎07-01-2023

what was that sorry?

anastasiou82 · ‎07-01-2023

The message i get (

show ip ospf

events) when the eBGP peering goes up

Flavio Miranda · ‎07-01-2023

Run this command with and without the BGP:

show ip ospf X  rib redistribution x.x.x.x

anastasiou82 · ‎07-01-2023

I will check it. Thanks al lot Flavio

Flavio Miranda · ‎07-01-2023

You´re welcome.

But, it seems it is related to protocol preference.

MHM Cisco World · ‎07-01-2023

can I see config of R1
R1-R2
both have eBGP and in same time there is OSPF between two routers ?
If Yes then eBGP have AD=20 and it prefer than OSPF=110

anastasiou82 · ‎07-01-2023

no, R1-R2 have only eBGP peering. R1 has ospf peering with other router.

MHM Cisco World · ‎07-01-2023

OK your static route have AD upper than 20 ?

show me config and show me show ip bgp and show ip route