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Redistributing default route receive from ISP via BGP into ospf

Hi,

my company have 2 links to the same ISP currently and the internal network is running ospf. Both my current internet facing routers actually are injecting default route into the ospf with the "default information originate" statement in the router ospf config. Under normal cases, the internal network is actually load balanced between the 2 links. However, when one of the upstream fails, 50% of the traffic would actually fails.

Is it possible to change my config, such that both my internet router redistribute the default route ,which they receive from their respective upstreams, into the internal ospf network?

With this, I think I can achieve 100% failover even though 1 of the link fails right?

Your help and advice is very much appreciated.

Thanks and regards,

Kim Pin

1 ACCEPTED SOLUTION

Accepted Solutions
Cisco Employee

Re: Redistributing default route receive from ISP via BGP into o

Kim,

The "default-information originate" w/o the "always" keyword will only orginate if you do have a default in the routing table.

The "always" keywork will force the origination whether you do have a default in the routing table or not.

So if you are receiving the default route dinamically on both links and are not using the "always" keyword, your failover should be fine.

As you loose a default route on one side, the Internet facing router will see the default route coming from OSPF (other Internet facing router) and will stop injecting the default in OSPF. All traffic destined to the Internet will then converge on the other Internet facing router.

Hope this helps,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
6 REPLIES
Cisco Employee

Re: Redistributing default route receive from ISP via BGP into o

Unless you use the always keyword, the "default- information originate" command will only inject the default route in ospf if you have a default gateway present in the routing table. So if you stop receiving the default from the ISP you stop injecting de default. Bear in mind that if the default present in the RIB is owned by OSPF (coming from the other Internet facing router) it will not be injected in OSPF by the local router.

The solution would e to remove the "always" if you use it.

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
New Member

Re: Redistributing default route receive from ISP via BGP into o

Thanks for your prompt reply.

Do you mean that as long as both my router has the gateway of last resort pointing to my next-hop towards my ISP and w/o the "always", the failover should be automatic??

But I don;t quite get regarding the default is present in the RIB? Would you mind elaborate further?

Currently all my internal routers will see their default route pointing to both the internet routers.

Rgds.

Cisco Employee

Re: Redistributing default route receive from ISP via BGP into o

Oh, I see you are statically pointing the default route to your ISP on the two Internet facing router.

The problem with the static is that it dissapears if the link protocol goes down but it doesn't if for some reason the link protocol is up but traffic doesn't get through (sometimes seen with FrameRelay).

The ideal would be to dynamically receive the default route from the ISP so if you loose one link to the ISP, you stop receiving the default and therfore stop injecting it in OSPF.

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
New Member

Re: Redistributing default route receive from ISP via BGP into o

Oops, I think you have misunderstood.

Yup, the 2 routers are indeed receiving default route from the ISP.

So I think everything should be fine right.

I have always thought "default-information originate" is a command to manually generate a default route into the OSPF. I guess I learn something new here.

As long as I don't receive the default route from my upstream, the statement will not kick in?? Am I right?

Cisco Employee

Re: Redistributing default route receive from ISP via BGP into o

Kim,

The "default-information originate" w/o the "always" keyword will only orginate if you do have a default in the routing table.

The "always" keywork will force the origination whether you do have a default in the routing table or not.

So if you are receiving the default route dinamically on both links and are not using the "always" keyword, your failover should be fine.

As you loose a default route on one side, the Internet facing router will see the default route coming from OSPF (other Internet facing router) and will stop injecting the default in OSPF. All traffic destined to the Internet will then converge on the other Internet facing router.

Hope this helps,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
New Member

Re: Redistributing default route receive from ISP via BGP into o

Hi Ritter,

Thanks for your info.

It's really great and helps clear my doubt.

Ciao..

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