Enable Proxy Arp; Routing Assistance When Ip Routing Is Disabled; Proxy Arp; Default Gateway - Cisco Catalyst 3750 Software Configuration Manual

Configuring IP Addressing

Enable Proxy ARP

By default, the switch uses proxy ARP to help hosts determine MAC addresses of hosts on other
networks or subnets.
Beginning in privileged EXEC mode, follow these steps to enable proxy ARP if it has been disabled:
Command
Step 1
configure terminal
Step 2 interface interface-id
Step 3 ip proxy-arp
Step 4
end
Step 5
show ip interface [interface-id]
Step 6 copy running-config startup-config
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 other networks when it does not have IP
routing enabled:
•
•
•

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 determine 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
section on page

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 an IP Control Message Protocol
(ICMP) redirect message back, defining which local router the host should use. The switch caches the
redirect messages and forwards each packet as efficiently as possible. A limitation of this method is that
there is no means of detecting when the default router has gone down or is unavailable.
Catalyst 3750 Metro Switch Software Configuration Guide
28-10
Proxy ARP, page 28-10
Default Gateway, page 28-10
ICMP Router Discovery Protocol (IRDP), page 28-11
28-10. Proxy ARP works as long as other routers support it.
Purpose
Enter global configuration mode.
Enter interface configuration mode, and specify the Layer 3
interface to configure.
Enable proxy ARP on the interface.
Return to privileged EXEC mode.
Verify the configuration on the interface or all interfaces.
(Optional) Save your entries in the configuration file.
Chapter 28 Configuring IP Unicast Routing
"Enable Proxy ARP"
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