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New Member

Poisoned RIP route

I have a router running RIP on a serial Interface and BGP on an Ethernet interface. I have a default-information originate command in the RIP process, and the default is being advertised by RIP with a metric of 1. There is no default in the routing table. When the router gets a default by BGP and puts it in the routing table, RIP starts advertising the default with a metric of 16. The RIP database has the default with a metric of 0. Redistributing BGP into RIP doesn't help.

Can any one explain me this behavior?

Thanks

Paulo

9 REPLIES
Cisco Employee

Re: Poisoned RIP route

Could you please post your config.

Thanks,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
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Anonymous
N/A

Re: Poisoned RIP route

Please see the attached file.

When I configure a default-metric in the RIP process, or when I use a route-map setting the metric on the routes redistributed from BGP to RIP, the default route is advertised with the configured. Otherwise, I always get that nasty metric of 16.

Thanks again.

Paulo

Gold

Re: Poisoned RIP route

The eBGP route is beating the RIP route in the routing table, I think, which means RIP doesn't have a default in the routing table, and poisons it's route. I don't think it should be acting this way with default information originate, it should see the default from BGP, and send out a default anyway.

To get around this, try removing default information originate, and redistribute from BGP into RIP. I know you said it does this with the redistributeion in, but I think you had the redistribution and the default information originate both in--try with just the redistribution.

Beyond this, the behaviour needs to be checked in the lab, and possibly have a defect filed against it. IF you want to pursue that path, please open a case with the TAC. If you can't, then email me off line, and I'll have someone check on it, if I can.

:-)

Russ.W

New Member

Re: Poisoned RIP route

It appears that the issue is you are not setting a default metric in RIP. Remember that the "default-information orginate" command is a specialized form of the "redistribute" command. Also remember that BGP and RIP can not understand each others metrics. If you do not tell RIP the metric type the route will not be redistributed.

The command you are looking for is "default-metric 1".

-Rob

New Member

Re: Poisoned RIP route

To add to my other post, the "default-information origiante" command will do one of two things, take a default route already learned and advertise it or it will send default when no other default exists.

The behaivor you are seeing is expected. When the BGP route is in the route table RIP will take this learned route and redistribute it to its neighbors. In your case RIP can not understand the BGP metric, default metric is not set, so the route is advertised as unreachable. When you shut down bgp and the default dissappears RIP begins to originate defualt because it has no other defualt route in its routing table. Since it is originated by RIP the metrics are understood and the route is learned.

HTH

Anonymous
N/A

Re: Poisoned RIP route

Yes, I had already tried that and it worked fine. It also works with a route-map in the "redistribute BGP" setting the metric value for the redistributed routes. Nevertheless, I find it odd that when there is no default route in the table it gets advertised, and when the default gets there by BGP, it becomes poisoned. This doesn't happen if the default is a static one, only when it is a BGP default (haven't tried other protocols, though...). And notice that in the RIP database the defaul-information originated route has a metric of 0, which makes things even stranger. I'll try to do some more testing as soon as the weekend is over :((

Paulo

New Member

Re: Poisoned RIP route

Not odd at all, Remember what you are doing with the "default-information originate" is redistributing the learned default route into RIP. When redistributing between routing protocols if neither the metric keyword nor the default-metric command specifies a metric the metric will default to 20 for routes redistributed into OSPF and to 0 for routes redistributed into other protocols. RIP can not have a hop count of 0, it must be between 1 and 16, so the route will not be redistributed.(hop count of 16) So basically if you are redistributing into RIP you need to set a metric or it will not work.

New Member

Re: Poisoned RIP route

To answer your question on why it works with a static route, RIP is able to automatically redistribute static routes. It assigns static routes a metric of 1. This makes sense too because RIP is able to make this metric translation pretty easily .. the static route is on this router so assign a metric of 1. Think about the BGP route ... BGP does not even use metrics per say .... so how can RIP translate BGP attributes into a a RIP metric.

Sorry about the long posts :-)

Anonymous
N/A

Re: Poisoned RIP route

I guess that makes sense, you have convinced me!

Thanks!

Paulo

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