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 and 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
Disabling RARP
RARP is enabled by default. To disable RARP, enter the following command at the global CONFIG level.
device(config)# no ip rarp
Syntax:
[no] ip rarp
To re-enable RARP, enter the following command.
device(config)# ip rarp
Creating static RARP entries
You must configure the RARP entries for the RARP table. The Layer 3 switch can send an IP address in reply to a client RARP request
only if create a RARP entry for that client.
Configuring IP parameters - Layer 3 switches
FastIron Ethernet Switch Layer 3 Routing
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