Basic Operation Guide 2014/02

and outgoing packets can potentially be sent by different paths at different times. This results in
different source IP addresses, which creates a client identification problem on the server site. For
example, there is no way to designate a fixed IP address for outgoing packets for RADIUS or
TACACS, so it is necessary to configure in the RADIUS or TACACS database all possible IP
addresses that are configured on the switch as valid clients. When using system logging, it can
be difficult to interpret the logging and accounting data on the server site as the same client can
be logged with different IP addresses.
To decrease the amount of administrative work involved, a configuration model is provided that
allows the selection of an IP address to use as the source address for all outgoing traffic generated
by a specified software application on the switch. This allows unique identification of the software
application on the server site regardless of which local interface has been used to reach the
destination server.
Specifying the source IP address
The CLI command ip source-interface is used to specify the source IP address for an application.
Different source IP addresses can be used for different software applications, but only one source
IP address can be specified for each application.
Syntax:
[no] ip source-interface <radius | sflow | sntp | syslog | tacacs |
telnet | tftp | all> <loopback<id> | vlan <vlan-id> address
<ip-address>>
Determines the source IP address used by the specified software application when
transmitting IP packets. The all parameter can be used to set one IP address for all
the listed applications.
The no version of the command cancels the configuration and the application
reverts to its default behavior. The system determines the source IP address of
outgoing application-specific IP packets at packet transmission time.
loopback <id> : Specifies that the IP address of the loopback interface is used as
the source IP address in outgoing packets. If the loopback interface has no IP
address, then the application reverts to the default behavior. If more than one IP
address is configured, then the lowest IP address is used.
vlan <vlan-id> : Specifies that the IP address of the indicated VLAN interface is
used as the source IP address of outgoing packets. If the specified VLAN interface
has no IP address configured, or is down, then the application reverts to the default
behavior. If more than one IP address is configured, then the lowest IP address is
used.
address <ip-address> : Specifies the IP address that should be used as the source
IP address of outgoing packets. The IP address must be a valid IP address configured
on one of the switch’s VLAN or loopback interfaces. If the interface is down, then
the application reverts to the default behavior.
118 Configuring IP Addressing