Filtering routing updates?

Answered Question
Aug 2nd, 2010

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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Correct Answer by Nagaraja Thanthry about 6 years 4 months ago

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

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Nagaraja Thanthry Mon, 08/02/2010 - 09:20

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

Correct Answer
Nagaraja Thanthry Mon, 08/02/2010 - 09:22

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

ivo.tzvetkov Mon, 08/02/2010 - 10:52

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

cheers!

ivo

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