Troubleshooting Ethernet Problems
269
The problem statement is that Ethernet 0/1 is functioning properly, but it can-
not communicate with Host Z. There is no listing for Host Z in the ARP table.
It is simpler to decide the possible causes and create an action plan by
focusing on the ARP table. What possible reasons are there for Host Z not
to be listed in the ARP table? Some reasons are as follows:
Failed host
Cabling failures
Bad Ethernet NIC on Host Z
Mismatching frame encapsulation type
Propose Solutions
You verified that the host is not down. No traffic is transiting the Ethernet
interface on the router. This indicates that the Ethernet card is not starting
to fail, but could have completely failed. Cabling is probably not the issue
because you would see interface resets or carrier transitions. None of those
symptoms are indicated on the interface. This leaves us with mismatching
encapsulation type as the probable problem.
The easiest way to test it is to ping Router C from Host Z. The results follow:
C:\WINDOWS>ping 172.16.60.1
Pinging 172.16.60.1 with 32 bytes of data:
Reply from 172.16.60.1: bytes=32 time=7ms TTL=255
Reply from 172.16.60.1: bytes=32 time=1ms TTL=255
Reply from 172.16.60.1: bytes=32 time=2ms TTL=255
Reply from 172.16.60.1: bytes=32 time=4ms TTL=255
Ping statistics for 172.16.60.1:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 1ms, Maximum = 7ms, Average = 3ms
C:\WINDOWS>
The ping was successful. Why is it that Router C can ping Host Z, but
Host Z cannot ping Router C? Let's go back to the router. Look at the ARP
table now.
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