Configuration Guide User guide

FastIron Configuration Guide 1007
53-1002494-02
Configuring IP parameters – Layer 3 Switches
Reverse Address Resolution Protocol configuration
The Reverse Address Resolution Protocol (RARP) provides a simple mechanism for
directly-attached IP hosts to boot over the network. RARP allows an IP host that does not have a
means of storing its IP address across power cycles or software reloads to query a directly-attached
router for an IP address.
RARP is enabled by default. However, you must create a RARP entry for each host that will use the
Layer 3 Switch for booting. A RARP entry consists of the following information:
• The entry number – the entry sequence number in the RARP table.
• The MAC address of the boot client.
• The IP address you want the Layer 3 Switch to give to the client.
When a client sends a RARP broadcast requesting an IP address, the Layer 3 Switch responds to
the request by looking in the RARP table for an entry that contains the client MAC address:
• If the RARP table contains an entry for the client, the Layer 3 Switch sends a unicast response
to the client that contains the IP address associated with the client MAC address in the RARP
table.
• If the RARP table does not contain an entry for the client, the Layer 3 Switch silently discards
the RARP request and does not reply to the client.
How RARP Differs from BootP and DHCP
RARP and BootP/DHCP are different methods for providing IP addresses to IP hosts when they
boot. These methods differ in the following ways:
• Location of configured host addresses:
- RARP requires static configuration of the host IP addresses on the Layer 3 Switch. The
Layer 3 Switch replies directly to a host request by sending an IP address you have
configured in the RARP table.
- The Layer 3 Switch forwards BootP and DHCP requests to a third-party BootP/DHCP server
that contains the IP addresses and other host configuration information.
• Connection of host to boot source (Layer 3 Switch or BootP/DHCP server):
- RARP requires the IP host to be directly attached to the Layer 3 Switch.
- An IP host and the BootP/DHCP server can be on different networks and on different
routers, so long as the routers are configured to forward (“help”) the host boot request to
the boot server.
- You can centrally configure other host parameters on the BootP/DHCP server, in addition
to the IP address, and supply those parameters to the host along with its IP address.
To configure the Layer 3 Switch to forward BootP/DHCP requests when boot clients and the boot
servers are on different subnets on different Layer 3 Switch interfaces, refer to “BootP and DHCP
relay parameter configuration” on page 1011.