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Catalyst 6500 Series Switch Software Configuration Guide—Release 8.7
OL-8978-04
Chapter 3 Configuring the Switch IP Address and Default Gateway
Understanding How Automatic IP Configuration Works
When you configure the IP address, subnet mask, broadcast address, and VLAN membership of the sc0
and sc1 interfaces, you can access the switch through Telnet or Simple Network Management Protocol
(SNMP). When you configure the SLIP (sl0) interface, you can open a point-to-point connection to the
switch through the console port from a workstation.
All IP traffic that is generated by the switch itself (for example, a Telnet session that is opened from the
switch to a host) is forwarded according to the entries in the switch IP routing table. For intersubnetwork
communication to occur, you must configure at least one default gateway for the sc0 or sc1 interfaces.
The switch IP routing table is used to forward traffic originating on the switch only; the routing table is
not used for forwarding traffic that is sent by the devices that are connected to the switch.
Understanding How Automatic IP Configuration Works
These sections describe how the switch can obtain its IP configuration automatically:
•
Automatic IP Configuration Overview, page 3-2
•
Understanding DHCP, page 3-3
•
Understanding BOOTP and RARP, page 3-4
Note
These sections apply only to the sc0 interface. The automatic IP configuration features do not apply to
the sc1 or sl0 interfaces.
Automatic IP Configuration Overview
The switch can obtain its IP configuration automatically using one of the following protocols:
•
Bootstrap Protocol (BOOTP)
•
Dynamic Host Configuration Protocol (DHCP)
•
Reverse Address Resolution Protocol (RARP)
The switch makes BOOTP, DHCP, and RARP requests only if the sc0 interface IP address is set to 0.0.0.0
when the switch boots up. This address is the default for a new switch or a switch whose configuration
file has been cleared using the
clear config all
command. BOOTP, DHCP, and RARP requests are only
broadcast out the sc0 interface.
Note
If the CONFIG_FILE environment variable is set, all configuration files are processed before the switch
determines whether to broadcast BOOTP, DHCP, and RARP requests. For more information about the
CONFIG_FILE environment variable, see
Chapter 25, “Modifying the Switch Boot Configuration.”