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Suspecting a bad FastEthernet Interface on Router 2651XM

Hi all,

I've connected two routers with each other through ethernet crossover cable on fastEthernet0/1, but I can't ping R1 from R2 or vice-versa.

My R1 fa0/1 has IP address and R2 fa0/1 has IP address The LEDs around the ports are lighted when the cable is connected and also when I do a show IP interface brief both status and protocol are up.  When I do a 'show CDP neighbours' it doesn't show the devices connected through that port.

After some tests done on all my router interfaces, I could determine that the problem was on only fa0/1 on Router 2. Only when I connected the routers through that port I could not ping.

Now I don't know if the problem is physical or software. Does anyone know how to perform some tests on that port to see if it's a good port?


Router#show ip int b
Interface IP-Address OK? Method Status Protocol
FastEthernet0/1 YES manual up up


Router#show cdp neighbors
Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
S - Switch, H - Host, I - IGMP, r - Repeater

Device ID Local Intrfce Holdtme Capability Platform Port ID


Router#show interfaces fa0/1
FastEthernet0/1 is up, line protocol is up
Hardware is AmdFE, address is 0013.1a26.0961 (bia 0013.1a26.0961)
Internet address is
MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Full-duplex, 100Mb/s, 100BaseTX/FX
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:09, output 00:00:09, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
212 packets input, 16926 bytes
Received 0 broadcasts, 0 runts, 2 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog
0 input packets with dribble condition detected
177 packets output, 60658 bytes, 0 underruns
0 output errors, 0 collisions, 1 interface resets
28 unknown protocol drops
0 babbles, 0 late collision, 0 deferred
19 lost carrier, 0 no carrier
0 output buffer failures, 0 output buffers swapped out

Jon Marshall
VIP Community Legend


Your post is confusing. 


You say the interfaces are and respectively and then the output below shows 


Have you tried putting both interfaces in the same IP subnet ?





I edited it, it's

Yes both ports connected  to each other are on the same IP subnet.


Point to point connections need to be on same subnet.  You have two different subnets here as indicated with the /24:


This will not work in this configuration.


I have two suggestions, either would work in my opinion:

1) Change the subnet mask to /16 so that the sub network would be (or)

2) change R2's interface to or vice versa (R1's interface to