ARP Guard

Note

ARP Guard is supported only on devices based on Extreme 8820, SLX 9740, SLX 9640, and SLX 9540.

Internet exchange points (IXPs) have a flat Layer 2 topology to provide any-to-any connectivity among BGP routers from connected ISPs, CSPs, and enterprises. As an IP host, each BGP peering router uses Address Resolution Protocol (ARP) to determine the MAC address of its BGP peers.

Because ARP is not a secure protocol, any BGP router can reply to the ARP request for any IP address. And any BGP router can generate gratuitous ARP to claim ownership of any IP address in the router. Valid traffic can be sent to the wrong destination in the following scenarios.

The IP address of a BGP router (connected to the IXP) is misconfigured.
The network administrator unknowingly turns on the ARP Proxy feature on the interface that faces the IXP.

ARP Guard, like DAI, is effective against the various methods of ARP poisoning. For more information, see ARP Poisoning.

The ARP Guard feature uses a set of ACL-like commands to build a table of allowed IP addresses on the link. As a result, when an ARP reply—either due to gratuitous ARP or in response to a normal ARP request—is received on a port facing the BGP router, the reply is compared to the table of allowed IP addresses. ARP packets that do not match the entries are dropped. Matching ARP packets are forwarded.

For more information about the ACL, see Create an ARP Access Control List.