My edge router is connected to one transit ISP full route table and to IXP. I would like to know what is the best way to protect the connection to IXP from becoming unwilling transit ISP. For example if one of the IXP members will point static route to my next hop for network that is not one of my prefixes he will be able to reach it because the edge router has full routing table and that way I will become unwilling ISP. I was finding about configuring an ACL on the ingress port from the IXP that permit traffic that only designated to my network prefixes. Is there any another way to do it ?



1 Answer 1


An ACL is a good idea to block this sort of behavior. You should also filter out any source addresses not belonging to the IXP networks to prevent spoofing. RFC 2827 talks about this as well, although their focus is on DoS attacks.

If you don't advertise the IXP networks to your ISP, then the return traffic will never come back to the IXP through you. So at worst, you would be part of an asymmetric path. If there is a stateful firewall somewhere in the path, that should drop the traffic flow.

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