ping and tracert

Unanswered Question
Oct 10th, 2007

Hello all,

When I was trying ping to 192.0.106.x it's not pinging. Will it trace-route with IP 192.0.106.x? if yes how experts can anybody suggest me.

Regards,

Naidu.

I have this problem too.
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spremkumar Wed, 10/10/2007 - 04:03

Hi

Have you assigned this ip anywhere in your network?

what you are exactly trying to do over there ?

regds

Kevin Dorrell Wed, 10/10/2007 - 04:35

Try it. A trace does not rely on the target responding, and will test each hop on the way. It is great for finding routing loops and black homes. Beware that not all the devices in the path will necessarily repond.

Try it, post the results here, and we will help you interpret them.

Be aware also that for ping to work, there must be a valid route to the destination, and also one from the destination back to the pinging machine.

Kevin Dorrell

Luxembourg

Richard Burts Wed, 10/10/2007 - 10:18

Kevin

I am not sure that I understand your comment about trace does not rely on the target responding. Certainly a traceroute may show useful information even if the target does not respond. But traceroute does need to get the port unreachable from the target to know when it is time to stop. If you meant that trace is not limited to responses from the target then I would agree with that. But to say not rely seems to me to be a bit too strong.

HTH

Rick

Kevin Dorrell Wed, 10/10/2007 - 11:49

Rick,

Sorry, I might have expressed myself badly there. What I meant was that the trace provides useful information even if the final destination is not responding. The original question seemed to imply "well if not even a ping is working, so what is the use of even trying a trace". What I was trying to put over (maybe unsuccessfully) was that getting useful information from a trace relies on each hop in the path responding, and not necessarily on the final destination.

I'll have to read back my postings better from the p.o.v. of the original question. Thanks for clarifying.

Kevin Dorrell

Luxembourg

Richard Burts Wed, 10/10/2007 - 12:02

Kevin

No problem. When I first read your response my reaction was that it was too strong about not rely on the target. I certainly did get the sense that part of your point was that there was useful information even if there is no response from the target - and I certainly agree with that. If fact if I try to ping something and the ping fails I almost always try a traceroute and hope to see how far I get and how I am getting there.

There is another aspect to consider. It is possible that traceroute may succeed even when ping fails. There may be an access list which is denying ping. If you are doing traceroute from an IOS device or from a _nix box then the traceroute is using USP packets and not the ping packets that tracert on Windows boxes uses. In this case the UDP based traceroute might succeed where the ping fails.

HTH

Rick

ilnaiduccna Wed, 10/10/2007 - 21:20

Hi Rick,

Great your explainations,

Your right in the way where ping fails but traceroute works fine you told that there may be any accesslist but there is no access list created, the targate system was off but till I am getting traceroute.

My query without communicate with destination PC how traceroute will works.

Regards,

Naidu.

Kevin Dorrell Wed, 10/10/2007 - 23:56

Naidu,

Traceroute follows the path through the network step by step, using thus procedure ..

First it generates a packet (or actually 3 of them) with a TTL (time to live) of 1 hop. This fails at the first router, but that router reports back to the source with a "TTL exceeded".

It then generates a set of packets with a TTL of 2 hops. These fail at the seocnd router, but it reports back to the source with a "TTL exceeded".

It then generates a set of packets with a TTL of 3 .... you get the picture.

Until finally it gets a response from the destination, and then it stops. Of course, if it doesn't get a response from the destinatio, it carries on up to a TTL of 30, then gives up.

This is very useful for detecting routing loops. If you see the same routers coming up several times throughout the path, then you know you have a loop. It also tells you where you might have a black hole; if you get no more responses after a certain router, then look for a black hole in that router.

Hope this helps.

Kevin Dorrell

Luxembourg

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