Cisco – Why Does Ping Work When Traceroute Fails?

ciscogns3pingtraceroute

If I can ping a router successfully, why is it that when I do traceroute, it stops at a particular interface and says "ICMP type:3, code:3, Destination port unreachable". Doesn't that mean that it can't make a connection?

Here's my topology:

When I ping the Default_Gateway from any of the VPCs, it works. But when I do trace command, it stops at some interface and gives the error message I mentioned above. Is there something wrong or is that how it is?

FA1 ping Default_Gateway:

FA1> ping 123.45.250.1
84 bytes from 123.45.250.1 icmp_seq=1 ttl=253 time=35.980 ms
84 bytes from 123.45.250.1 icmp_seq=2 ttl=253 time=51.959 ms
84 bytes from 123.45.250.1 icmp_seq=3 ttl=253 time=31.955 ms
84 bytes from 123.45.250.1 icmp_seq=4 ttl=253 time=45.929 ms
84 bytes from 123.45.250.1 icmp_seq=5 ttl=253 time=40.067 ms

FA1 trace Default_Gateway: 

FA1> trace 123.45.250.1
trace to 123.45.250.1, 8 hops max, press Ctrl+C to stop
 1   123.45.8.1   8.898 ms  12.988 ms  8.000 ms
 2   123.45.250.5   22.986 ms  20.991 ms  19.013 ms
 3   *123.45.250.1   30.978 ms (ICMP type:3, code:3, Destination port unreachable)

Best Answer

That is because ping uses ICMP Echo Request and ICMP Echo Reply. Your traceroute is using UDP, which uses addresses called ports. Apparently, the port you are using in the traceroute commend is closed or denied on the destination, and the destination sends back an ICMP error message because of that. You didn't give the configuration for the Default Gateway router, so we cannot telly you the specific reason for the error.

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