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Broadcast problems occur when a broadcast IP address is configured on the sc0 management interface of a Cisco Catalyst 6500 switch

Core issue

The routers to which the Cisco Catalyst 6500 switches connect can show a lot of broadcasts from various hosts on the network to this broadcast address.

Cisco Catalyst 6000 family switches have two network interfaces that can be configured:

  • In-band interface (sc0)
  • Serial Line Internet Protocol (SLIP) interface (sl0)

Configuration of the sc0 interface with an IP address and subnet mask provides access to the command line interface (CLI) of the switch through Telnet from a remote host. Assign the sc0 interface to an active VLAN configured on the switch. The default VLAN is VLAN 1. Ensure that the assigned IP address is in the same subnet as the other stations in that VLAN.

A netmask indicates the number of bits allocated to subnetting in the host ID section of the specified class A, B, or C address. For example, if the IP address of the sc0 interface is, the host ID has 16 bits for this class B address. Any number of bits in the host ID can be allocated to the subnet field. If no netmask is specified, the number of bits is assumed to be the natural netmask.


To resolve any broadcast issues or error messages in the network, remove the broadcast IP address, because the broadcast IP address is optional. Issue the set interface sc0 command to configure the in-band interface on the switch.

For more information, refer to the Configure the sc0 Interface on Catalyst 6500/6000 Switches That Run CatOS section of Configuring a Management IP Address on Catalyst 4500/4000, 5500/5000, 6500/6000, and Catalyst Fixed Configuration Switches.