Cisco Systems 3750E manual Configuring Broadcast Packet Handling, 38-14

Chapter 38 Configuring IP Unicast Routing

Configuring IP Addressing

	Command	Purpose
Step 6
	ip irdp maxadvertinterval seconds	(Optional) Set the IRDP maximum interval between advertisements. The
		default is 600 seconds.
Step 7
	ip irdp minadvertinterval seconds	(Optional) Set the IRDP minimum interval between advertisements. The
		default is 0.75 times the maxadvertinterval. If you change the
		maxadvertinterval, this value changes to the new default (0.75 of
		maxadvertinterval).
Step 8	ip irdp preference number	(Optional) Set a device IRDP preference level. The allowed range is –231
		to 231. The default is 0. A higher value increases the router preference
		level.
Step 9
	ip irdp address address [number]	(Optional) Specify an IRDP address and preference to proxy-advertise.
Step 10
	end	Return to privileged EXEC mode.
Step 11
	show ip irdp	Verify settings by displaying IRDP values.
Step 12
	copy running-config startup-config	(Optional) Save your entries in the configuration file.

If you change the maxadvertinterval value, the holdtime and minadvertinterval values also change, so it is important to first change the maxadvertinterval value, before manually changing either the holdtime or minadvertinterval values.

Use the no ip irdp interface configuration command to disable IRDP routing.

Configuring Broadcast Packet Handling

After configuring an IP interface address, you can enable routing and configure one or more routing protocols, or you can configure the way the switch responds to network broadcasts. A broadcast is a data packet destined for all hosts on a physical network. The switch supports two kinds of broadcasting:

•A directed broadcast packet is sent to a specific network or series of networks. A directed broadcast address includes the network or subnet fields.

•A flooded broadcast packet is sent to every network.

Note You can also limit broadcast, unicast, and multicast traffic on Layer 2 interfaces by using the storm-controlinterface configuration command to set traffic suppression levels. For more information, see Chapter 26, “Configuring Port-Based Traffic Control.”

Routers provide some protection from broadcast storms by limiting their extent to the local cable. Bridges (including intelligent bridges), because they are Layer 2 devices, forward broadcasts to all network segments, thus propagating broadcast storms. The best solution to the broadcast storm problem is to use a single broadcast address scheme on a network. In most modern IP implementations, you can set the address to be used as the broadcast address. Many implementations, including the one in the switch, support several addressing schemes for forwarding broadcast messages.

Perform the tasks in these sections to enable these schemes:

•Enabling Directed Broadcast-to-Physical Broadcast Translation, page 38-15

•Forwarding UDP Broadcast Packets and Protocols, page 38-16

•Establishing an IP Broadcast Address, page 38-17

•Flooding IP Broadcasts, page 38-17

	Catalyst 3750-E and 3560-E Switch Software Configuration Guide
38-14	OL-9775-02