Dell POWEREDGE M1000E - Manual (Page 905)

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Cisco Catalyst Blade Switch 3130 and 3032 for Dell Software Configuration Guide
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Chapter 38 Configuring IP Unicast Routing
Configuring IP Addressing
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. The host that sent the request then 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 returns an IP Control Message Protocol
(ICMP) redirect message, identifying the local router that the host should use. The switch caches the
redirect messages and forwards each packet as efficiently as possible. This method cannot detect when
the default router has failed or is unavailable.
Beginning in privileged EXEC mode, follow these steps to define a default gateway (router) when IP
routing is disabled:
Use the no ip default-gateway global configuration command to disable this function.
ICMP Router Discovery Protocol (IRDP)
Router discovery allows the switch to dynamically learn about routes to other networks by using ICMP
Router Discovery Protocol (IRDP). Hosts use IRDP to locate routers. When operating as a client, the
switch generates router discovery packets. When operating as a host, the switch receives router discovery
packets. The switch can also receive Routing Information Protocol (RIP) routing updates and use this
information to infer locations of routers. The switch does not actually store the routing tables sent by
routing devices; it merely keeps track of which systems are sending the data. The advantage of using
IRDP is that it allows each router to specify both a priority and the time after which a device is assumed
to be down if no more packets are received.
Each device discovered becomes a candidate for the default router, and a new highest-priority router is
selected when a higher priority router is discovered, when the current default router is declared down,
or when a TCP connection is about to time out because of excessive retransmissions.
Command Purpose
Step 1 configure terminal Enter global configuration mode.
Step 2 ip default-gateway ip-address Set up a default gateway (router).
Step 3 end Return to privileged EXEC mode.
Step 4 show ip redirects Display the address of the default gateway router to verify the
setting.
Step 5 copy running-config startup-config (Optional) Save your entries in the configuration file.