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New Member

Filtering routing updates?

Hello folks!

I have troubles understanding the following thing: how do ISPs filter  out/ prevent a LAN from receiving any broadcast advertised routing  protocols? Today, for the fist time, I stared wireshark, to listen to my  ISP's wire, and apart from dhcp, I heard nothing else. Do they manually  filter this via ACL (if yes - any examples?)? What is the common  practice to keep your lan segments "in dark" so that when you advertise a RIP network, the access layer/ end user gets only the traffic it has requested for? Thanks  :)

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Cisco Employee

Re: Filtering routing updates?

Also, to add to my earlier post, they use a static route for the subnets that the customer owns and point it towards customers router. Internally, they could redistribute the static route to their routing protocol or they could use BGP to redistribute those subnets.

Hope this helps.

Regards,

NT

3 REPLIES
Cisco Employee

Re: Filtering routing updates?

Hello,

Typically, the ISP's do not run a routing protocol on the customer facing interfaces unless they have an arrangement with the customer. If, for some reason, they do have to run the routing protocol, they can configure the interface facing the customer a passive interface thereby suppressing all routing updates.

Hope this helps.

Regards,

NT

Cisco Employee

Re: Filtering routing updates?

Also, to add to my earlier post, they use a static route for the subnets that the customer owns and point it towards customers router. Internally, they could redistribute the static route to their routing protocol or they could use BGP to redistribute those subnets.

Hope this helps.

Regards,

NT

New Member

Re: Filtering routing updates?

Yes Nagaraja, that sounds about right! Appreciate your response!

cheers!

ivo

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