[c-nsp] router ethernet

[Kern, Tom]

I have a 1700 router which is my internet router. it has a frame-relay serial int and an etherent int.
About twice a month, the ethernet int dies. Actually, it says eth0 up, line protocol up but i can't connect to the internal network from the router. I can however ping out on the frame.
The eth int is connected to a watchguard firewal via a crossover cable. Both ints on the router and firewall are set to manual and full duplex.
I can see some connections coming in on the firewall and connections going out but there is no internet access.
I'm pretty sure its not the firewall.

Does anyone know how to troubleshoot this further. any debug or logging to turn on?
are there situations when an int is not working but shown as up on a router?

here is my sh ver-


Cisco Internetwork Operating System Software
IOS (tm) C1700 Software (C1700-BNR2Y-M), Version 12.1(1), RELEASE SOFTWARE (fc1)
Copyright (c) 1986-2000 by cisco Systems, Inc.
Compiled Tue 14-Mar-00 17:45 by cmong
Image text-base: 0x80008088, data-base: 0x807F6DF4

ROM: System Bootstrap, Version 12.0(3)T, RELEASE SOFTWARE (fc1)

charmer-gw uptime is 25 minutes
System returned to ROM by power-on
System image file is "flash:aaa1390.bin"

cisco 1720 (MPC860) processor (revision 0x601) with 24576K/8192K bytes of memory
.
Processor board ID JAD05100NZY (3916151569), with hardware revision 0000
M860 processor: part number 0, mask 32
Bridging software.
X.25 software, Version 3.0.0.
1 Serial network interface(s)
WIC T1-DSU
32K bytes of non-volatile configuration memory.
8192K bytes of processor board System flash (Read/Write)

Configuration register is 0x2102

I know the ios is out of date.

thanks!