said by ps56k:1 - the interconnecting cable
2 - the Linksys BEFSR41 router
3 - the Speedstream 5100 DSL modem
I've witnessed this before with a SR11 and SR81.
Bad Ethernet cable in both cases.
If changing the cable does not solve the problem, then I speculate either the WAN port on SR41 is failing or the Ethernet port on modem is failing.
Be sure to remove power from the modem and SR41 while changing the Ethernet cable. I've witnessed 'hot swapping' the WAN cable on some Linksys devices can cause the very same problem you've described.
