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35-13
Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
OL-9639-06
Chapter 35 Configuring IP Unicast Routing
Configuring IP Addressing
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-control interface configuration command to set traffic suppression levels. For more information,
see Chapter 22, “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 35-13
• Forwarding UDP Broadcast Packets and Protocols, page 35-14
• Establishing an IP Broadcast Address, page 35-15
• Flooding IP Broadcasts, page 35-16
Enabling Directed Broadcast-to-Physical Broadcast Translation
By default, IP directed broadcasts are dropped; they are not forwarded. Dropping IP-directed broadcasts
makes routers less susceptible to denial-of-service attacks.
You can enable forwarding of IP-directed broadcasts on an interface where the broadcast becomes a
physical (MAC-layer) broadcast. Only those protocols configured by using the ip forward-protocol
global configuration command are forwarded.
You can specify an access list to control which broadcasts are forwarded. When an access list is
specified, only those IP packets permitted by the access list are eligible to be translated from directed
broadcasts to physical broadcasts. For more information on access lists, see
Chapter 31, “Configuring
Network Security with ACLs.”