BGP or OSPF default route ?

[Ivan Raic]

Fellow Cisco Friends,

Have a situation where a site is multihoming using 2 different local routers and 2 different ISPs, with full routing table received from both ISPs.

iBGP is setup between the local routers, and OSPF is used as IGP to the internal network.

The issue at hand though is that obivously im not going to redistribute the entire internet table to OSPF, just the default (0.0.0.0) network.

Problem is though the ISPs are not sending 0.0.0.0, dont want to use OSPF default-information originate always bc i want the default removed when the link to the ISP drops.

So the only option i can think of is using IP SLA, with static route & tracking.

But is there a better method, where if there is BGP neighbor default route is set, and when not neighboring there is no default route ?

Thanks,

Ivan.

[kozorezdi]

Hi Ivan,

Please tell me why the scheme like this will not working properly:

ISP1(.2)-------172.16.0.0/30-------(.1)R1

R1:

ip route 0.0.0.0 0.0.0.0 172.16.0.2

router ospf 10

  default-information originate

ISP2(.6)-------172.16.0.4/30-------(.5)R2

ip route 0.0.0.0 0.0.0.0 172.16.0.6

router ospf 10

  default-information originate

For the lab enviroment is it working, but in real life?

If the you have R1---R3---R2, than OSPF will share loading outgoing traffic via equal cost links to ISPs.

Have I missed something?

--

Have a nice day,

Dimitry

[Ivan Raic]

Hi Dimitry,

Thanks for the response.

The issue i find with static routes is that if the link drops to the ISP, but the interface still shows as UP/UP (which u get on a lot of metro ethernet services) it will be advertising to a black hole, unless of course you use IP SLA, with tracking on the static route.

After doing some research, i found that -

default-information originate always route-map name

Could be a possible solution, which i might test tomorrow.

According to some of my reading this will advertise a default route if the route-map matches any routes in the routing table, hence a internet route. But which internet route do i use bc i dont want it to disappear..

Ivan.

[kozorezdi]

Hi Ivan,

thank you for your post. interesting idea, good luck!

--

Dimitry

[Jon Marshall]

Ivan

As far as i know, no there is method to do this. The easiest solution is just to talk to your ISPs and ask for them to send a default-route as well.

If the won't then yes, IP SLA would be the way to go.

Jon

[Ivan Raic]

Hi JOn,

Yes i was thinking the same thing.

But wanted to leave that as my last resort, which might have to be the case..

THanks,

Ivan.

[smitesh kharecha]

Hi Ivan,

As far as i have understood and know,

either ISP needs to provide default route, so that you can have what you required.

or else.

track, IP SLA and static routing is to your rescue.

Regards,

Smitesh