MSN Messenger and NAT Routers
This is from the Linksys site:
Product Class:Routers, Other,
Operating System:Win 95, Win 98, Win ME, Win NT4.0, Win 2000,
P R O B L E M
My NAT (Network Address Translation) Router will not work with the MSN Messenger's File transfer or Voice connections.
S O L U T I O N
As explained on Microsoft's support page, Client computers that use a NAT router are not able to use MSN, The Microsoft Network Messenger Service version 3.0 program to transfer files or establish voice connections. This problem occurs because MSN Messenger file transfer and voice features do not work through NAT routers because there is no NAT editor to correctly translate the IP header information.
This is MSN Messenger's software limitation. Linksys Routers will not be able to bypass this until an appropriate NAT editor is available.