I am having some problems creating a SPAN port on my Cisco 871 (running IOS 12.4-11T).
My 871 is connected to a DSL modem, and uses "IP Negotiated" to get its dynamic ip address.
I want to monitor the WAN port (FastEthernet4) using SPAN, but when I type "monitor session 1 source interface FastEthernet4" into the cli, it is rejected. I can successfully use any of the other FastEthernet ports, as well as Vlan1 as a source for the SPAN session.
I have tried to use Dialer0 instead of FastEthernet4, but it still doesnt work.
Does anyone know what I am doing wrong? I could swear that I had this exact problem a few years ago....but for the life of me I cant remember how, or if, I was able to solve it.