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IPV4 Anycast workaround

Hi,

I am trying to configure an IPV4 anycast ip address. Its basically anycast IP with just routing.

In Short: (topology shown below)

I have ip address 3.3.3.3  in an ospf area 0 and same ip address 3.3.3.3 in another ospf area0 but in different domain.

The edge routers R3 and R4 connect these areas by BGP. When advertise the routes from BGP to OSPF the routing table on R4 or R3 will take the BGP route as it AD is less than OSPF.

My goal is to have 3.3.3.3 on each of the routers R3/R4 routing table by OSPF and then if it fails I can use the BGP route..Is there any work around for these?

3.3.3.3<--OSPF-->R1<--OSPF-->R2<-OSPF--->R3   <--BGP-->  R4<--OSPF-->R5<--OSPF-->R6<---->3.3.3.3

Thanks.

3 REPLIES
Cisco Employee

Re: IPV4 Anycast workaround

Hi,

Instead of advertising 3.3.3.3/32, can you aggregate 3.3.3.0/30 on both R3/R4 to BGP? This way, you don't need to worry about the OSPF vs BGP AD, local learned /32 is always preferred.

HTH,
Lei Tian

Sent from Cisco Technical Support iPhone App

IPV4 Anycast workaround

Thanks Lei,

I tried it and it didnt work. I think because BGP's AD is 20 and ospf is 110, so the AD will overcome the longest match for route selection..

Cisco Employee

Re: IPV4 Anycast workaround

Hi,

Longer match is always prefered. What you have from 'show ip route 3.3.3.3'?

HTH,

Lei Tian

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