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Catalyst 3550 Multilayer Switch Software Configuration Guide
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Chapter22 Configuring IP Unicast Routing
Configuring IP Addressing
This is an example of output form the show ip interface privileged EXEC command for Gigabit Ethernet
interface 0/3, where proxy ARP is enabled.
Switch# show ip interface gigabitethernet0/3
GigabitEthernet0/3 is up, line protocol is down
Internet address is 10.1.3.59/24
Broadcast address is 255.255.255.255
Address determined by setup command
MTU is 1500 bytes
Helper address is not set
Directed broadcast forwarding is disabled
Multicast reserved groups joined: 224.0.0.1 224.0.0.2
Outgoing access list is not set
Inbound access list is not set
Proxy ARP is enabled
Local Proxy ARP is disabled
Security level is default
Split horizon is enabled
ICMP redirects are always sent
ICMP unreachables are always sent
ICMP mask replies are never sent
IP fast switching is enabled
IP fast switching on the same interface is disabled
IP Flow switching is disabled
IP CEF switching is enabled
IP CEF Fast switching turbo vector
IP multicast fast switching is enabled
IP multicast distributed fast switching is disabled
IP route-cache flags are Fast, CEF
Router Discovery is enabled
IP output packet accounting is disabled
IP access violation accounting is disabled
TCP/IP header compression is disabled
RTP/IP header compression is disabled
Probe proxy name replies are disabled
Policy routing is disabled
Network address translation is disabled
WCCP Redirect outbound is disabled
WCCP Redirect exclude is disabled
BGP Policy Mapping is disabled
Routing Assistance When IP Routing is Disabled
These mechanisms allow the switch to learn about route s t o ot her ne tw ork s whe n it does not ha ve IP
routing enabled:
Proxy ARP, page 22-14
Default Gateway, page 22-15
ICMP Router Discovery Protocol (IRDP), page 22-15

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 subnet s. 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 i ts own