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Cisco Catalyst Blade Switch 3130 for Dell Software Configuration Guide
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Chapter38 Configuring IP Unicast Routing
Configuring IP Addressing

Enable Proxy ARP

By default, the switch uses proxy ARP to help hosts learn MAC addresses of hosts on other networks or
subnets.
Beginning in privileged EXEC mode, follow these steps to enable proxy ARP if it ha s b een disa bled :
To disable proxy ARP on the interface, use the no ip proxy-arp interface configuration command.
Routing Assistance When IP Routing is Disabled
These mechanisms allow the switch to learn about routes to ot her net works whe n it does not have IP
routing enabled:
•Proxy ARP, page38-12
•Default Gateway, page38-12
•ICMP Router Discovery Protocol (IRDP), page 38-13

Proxy ARP

Proxy ARP, the most common method for learning about other routes, enables an Ethernet host with no
routing information to communicate with hosts on other networks or subnets. The host assumes that all
hosts are on the same local Ethernet and that they can use ARP to learn their MAC addresses. If a switch
receives an ARP request for a host that is not on the same network as the sender, the switch evaluates
whether it has the best route to that host. If it does, it sends an ARP reply packet with its own Ethernet
MAC address, and the host that sent the request sends the packet to the switch, which forwards it to the
intended host. Proxy ARP treats all networks as if they are local and performs ARP requests for every
IP address.
Proxy ARP is enabled by default. To enable it after it has been disabled, see the “Enable Proxy ARP”
section on page 38-12. Proxy ARP works as long as other routers support it.

Default Gateway

Another method for locating routes is to define a default router or default gateway. All nonlocal packets
are sent to this router, which either routes them appropriately or sends a n IP Con trol Mes sag e Pr otoc ol
(ICMP) redirect message back, defining which local router the host should use. The switch caches the
redirect messages and forwards each packet as eff i ciently a s po ssib le. A li mitatio n of this m ethod i s tha t
there is no means of detecting when the default router has gone down or is unavailable.
Command Purpose
Step1 configure terminal Enter global configuration mode.
Step2 interface interface-id Enter interface configuration mode, and specify the Layer 3
interface to configure.
Step3 ip proxy-arp Enable proxy ARP on the interface.
Step4 end Return to privileged EXEC mode.
Step5 show ip interface [interface-id] Verify the configuration on the interface or all interfaces.
Step6 copy running-config startup-config (Optional) Save your entries in the configuration file.