HI Wilberth, It actually depends on what routing protocol is being used as a CE-PE routing protocol. The way prefixes are filtered is different for every protocol (BGP / OSPF / RIP / EIGRP etc).
There are Two steps to filtering prefixes: 1. Identify / Classify what needs to be blocked - using ACl / Prefix-lists 2. Filter the prefixes using tools specific to rouitng protocol being used. To Identify / Classify the prefixes: Then again you can either use an access-list or a prefix list to identify / classify the prefixes that you need to take action on. (Tip - An access list was originally designed to filter traffic off interfaces, whereas a prefix-list was designed to classify prefixes). I would personally use a prefix-list in this case. Example of access-list blocking Private (RFC 1918 addresses): access-list 1 deny 10.0.0.0 0.255.255.255 access-list 1 deny 172.16.0.0 0.15.255.255 access-list 1 deny 192.168.0.0 0.0.255.255 access-list 1 permit any (As there is implicit deny at the end of every access-list). Example of prefix-list ip prefix-list Deny_private seq 5 deny 10.0.0.0/8 le 32 ip prefix-list Deny_private seq 10 deny 172.16.0.0/12 le 32 ip prefix-list Deny_private seq 15 deny 192.168.0.0/16 le 32 ip prefix-list Deny_private seq 20 permit 0.0.0.0/0 le 32 Filtering The prefixes: You can use route-maps / distribute-lists / prefix-lists command to filter the prefixes. How & where you filter depends on what routing protocol you are using. Hope this helps! Regards, Naren ________________________________ From: Wilberth E. Lemaître <[email protected]> To: "[email protected]" <[email protected]> Sent: Thursday, 22 August 2013 4:52 AM Subject: [OSL | CCIE_RS] Route Filtering Hello community, I have a question in regards a topology I have been working on, you can find it attached.I must create a filter on the ISP routers so they can throw private routes if any company advertise them. I know this can be accomplish with a route map but I have no idea how to create that filter.As you can see there are 2 ISP, they must throw all the routes that are coming from any company.If you guys can help, would be well appreciate it. Best regards,Wilberth _______________________________________________ For more information regarding industry leading CCIE Lab training, please visit www.ipexpert.com Are you a CCNP or CCIE and looking for a job? Check out www.PlatinumPlacement.com http://onlinestudylist.com/mailman/listinfo/ccie_rs _______________________________________________ For more information regarding industry leading CCIE Lab training, please visit www.ipexpert.com Are you a CCNP or CCIE and looking for a job? Check out www.PlatinumPlacement.com http://onlinestudylist.com/mailman/listinfo/ccie_rs
