Enterasys Networks X-PeditionTM manual ARP and Proxy ARP, Proxy DNS, BOOTP/DHCP Relay

General IP Features

•Virtual Router Redundancy Protocol (VRRP): RFC-2338 and Definitions of Managed Objects

for the Virtual Router Redundancy Protocol: RFC-2787

•Equal-Cost Multi-Path (ECMP) per packet and per flow (round robin) for OSPF, BGP and static routes (RIP excluded)

–Unequal cost multi-path, redistribution of equal-cost paths, and multiple default routes based on default networks with multiple equal-cost next hops are not supported

ARP and Proxy ARP

ARP (Address Resolution Protocol) is a link-level protocol which provides a mapping between the two different forms of addresses: 32-bit IP addresses and hardware addresses used by the data link. The protocol dynamically keeps entries in the ARP Table and can accept statically configured entries according to RFC-826.

The arp command adds or deletes permanent entries to the ARP Table while the arp-timeoutcommand sets the duration for an ARP entry to stay in the ARP table before expiring. The show ip arp command displays real-time entries in the ARP table.

Proxy ARP lets the XSR answer ARP requests on one network for a host on another network. The router acts as a proxy agent for the destination host, relaying packets to it from other hosts, as defined by RFC-1027. It is configured with the ip proxy-arpcommand.

Proxy DNS

Proxy servers act as intermediaries between DNS clients and servers. They handle outgoing queries and answer them from data obtained by sending one or more queries to other DNS servers. Typically, they cache data received, reducing traffic and latency if the data are frequently requested.

XSR’s forwarding proxy server talks to other proxy or DNS servers without performing DNS resolution. They simply forward request and replies, relying on real DNS servers for name resolution, and cache the replies to avoid having to request resolution again with these benefits::

•A proxy DNS server releases the function of the resolver on the client side, and by doing so simplifies client implementation.

•Since the proxy acts as an intermediary between DNS clients and servers, no direct connection between clients and servers is needed.

•Instead of caching the DNS database in each client, proxy DNS maintains a centralized cache for DNS resolution.

You can enable DNS proxy with ip proxy-dns enable, specify a proxy server with ip proxy- dns name-server, clear the DNS cache table with clear ip proxy-dns cache, verify DNS settings with show running-config, and display DNS cache settings with show ip proxy-dns cache.

BOOTP/DHCP Relay

The Bootstrap Protocol (BOOTP) is used by systems with no capability of learning their IP addresses. BOOTP requests can be forwarded by routers, not necessitating one server on each physical network. Normally, BOOTP/DHCP requests are not forwarded, since they are local broadcasts which are not designed to be forwarded, and they have an invalid nonroutable IP source address, such as 0.0.0.x. But the agent replaces the destination address with a helper address, and the source address with its own address, then forwards it. You can set the helper address with the ip helper-addresscommand.

5-4 Configuring IP