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Cisco Router Name not showing its name when doing a traceroute

Posted on 2007-11-29
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Last Modified: 2008-02-01
Hi i'm trying to give my router a name so that when I run a traceroute from within the network and from outside the network it shows a name.

I keep getting time-outs when it hits the router and then it moves on. This is on a cisco.
I placed the hostname in and the domain name but it seems that's not it. Any ideas?
I get the following when I do the traceroute:

11     *        *        *     Request timed out.
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Question by:ntmyflt
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3 Comments
 
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by:wingatesl
ID: 20379707
make sure you are permiting all ICMP on the router

    access-list 110 permit icmp any any echo
    access-list 110 permit icmp any any echo-reply
    access-list 110 permit icmp any any time-exceeded
    access-list 110 permit icmp any any traceroute
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CCIE8122 earned 500 total points
ID: 20380082
this could actually be two problems.  1) connectivity, and 2) DNS.

1) connectivity: the fact that the trace times out at the router indicates that it is not responding to the traceroute, which could either be because there is a breakage (i.e., circuit or router is down), or more likely, as wingatesl suggests, the traceroute is being filtered.  As you appear to indicate that subsequent devices respond to the traceroute, the issue is almost certainly not a breakage, but a filter.  Again, as wingatesl recommends, make sure you allow ICMP in any access-lists, but note that this ACL may or may not be on the router itself, it could be on another device adjacent, or anywhere in between the tracing host and the router.

however, once you fix the first issue, you will almost certainly run into a second . . .

2) DNS: configuring a hostname and domain-name on the router have nothing to do with your problem, that only determines how the router sees itself and interacts with the DNS.  your problem is that the IP addresses on this 2800's interfaces do not have PTR records in the zone to which they (the IP addresses) belong.  That is, there exist no reverse DNS records for the IP addresses of your router's interfaces.  The exception to this is if one of the interfaces is connected to an IP circuit (Internet or MPLS) provided by a carrier/ISP.  In that case, the interface will have a /30 that belongs to the carrier/ISP and will already have a reverse DNS record that lies within the carrier/ISP's DNS zone, something like "ny-edge-04.inet.att.com," and no matter what DNS name you associate with that IP address will not matter, since the reverse DNS zone is owned by the carrier, and they likely will not change it.  The upshot is in this case, that you will always see a DNS name, it just will never be one you set.  

The reason you have to check both interfaces, is that it depends on which direction you do the traceroute from.  The router will respond to a traceroute with a source IP address of the interface that is closest to the tracing host.  So, if you are tracing from the Internet, this will be the IP address of the serial interface connected to your ISP.  If from the inside of your network, the Ethernet interface connected to your firewall.  The good news is that you have (or can have, if you request the carrier delegate the rDNS zone to you) adminstrative control of the rDNS zone for the IP block that the inside interface of the router connects to.  So you can create an rDNS zone with an entry for the IP address of the inside interface of the router, and voila, you will get name resolution for traceroutes to that hop.  But again, you have to resolve the connectivity issue first, before any DNS fixes will be noticed.

HTH

kr
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Author Comment

by:ntmyflt
ID: 20380180
Awesome responses guys. I'll give it a run and let you know, much appreciated!
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