Restricting the outgoing source IP address of the explicit web proxy
You can use the following command to restrict the source address of outgoing web proxy packets to a single IP address. The IP address that you specify must be the IP address of an interface that the explicit HTTP proxy is enabled on. You might want to use this option if the explicit HTTP proxy is enabled on an interface with multiple IP addresses.
For example, to restrict the outgoing packet source address to 172.20.120.100:
config http-proxy explicit
set outgoing-ip 172.20.120.100
end