Source IP address for various packet types

When a device originates a packet of one of the following types, the default source address of the packet is the lowest-numbered IP address on the interface that sends the packet:

• Telnet
• TACACS/TACACS+
• TFTP
• RADIUS
• Syslog
• SNTP

You can configure the device to always use the lowest-numbered IP address on a specific Ethernet, loopback, or virtual interface as the source addresses for these packets. When configured, the device uses the same IP address as the source for all packets of the specified type, regardless of the ports that actually sends the packets.

Designating a source IP address provides the following benefits:

• If your server is configured to accept packets only from specific IP addresses, you can configure the device to always send the packets from the same link or source address.
• If you specify a loopback interface as the single source for specified packets, servers can receive the packets regardless of the states of individual links. Thus, if a link to the server becomes unavailable, but can be reached through another link, the client or server still receives the packets, and the packets still have the source IP address of the loopback interface.