Comments on: cannot ping from router-2

By: bobkberg

bobkberg — Fri, 27 May 2005 11:56:00 +0000

Do a search on Ping in the web site archives. There was a recent thread on this exact subject within the last week or two. Since it’s quieted down, I’ve already deleted it, or would send you the reference number.

Bob

By: xevier

xevier — Fri, 27 May 2005 00:02:18 +0000

hi,
thanks to all of you for your interest and persistance,the problem is solved ultimately .it was a loose connection at a point.the fault was not observed in loop test but a small blink after a very long dalay in trans.we were suspecting router configuration instead.

but one more thing i want to ask– sometimes when we try ping we get successful ping from a pc command prompt but not from router(CLI). the pc traffic itself goes from the router.then why?the pc is able to ping but router is not.what is the difference between the two?

By: poppaman2

poppaman2 — Thu, 26 May 2005 08:40:38 +0000

I agree that it sounds like some sort of interference or line/signal quality. IF this is xDSL, be aware that it is sensitive to all sorts of strange issues: are there any new neon lights in the area (not necessarily on your customer’s premises)? Does the line run near any flourescent lights? (I have seen a case where a DSL connection in a basement office worked fine until the overhead lights were turned on…)?

One way to eliminate the external (Telco) connection is to connect the LECAR at the NID and ping: do you still get packet loss? If so, contact the telco; if not, the issue is internal to your customer’s location…

The fact that this started happening two (?) weeks ago points to some new environmental variable…

By: richarddoe

richarddoe — Thu, 26 May 2005 07:44:07 +0000

Don’t forget to double check speed and duplex settings for mismatch. Seen too many times where a router or switch was reset and the config changes weren’t written to NVRAM. This would explain the change in behavior and a mismatch would explain the packet loss.

By: johnbf

johnbf — Thu, 26 May 2005 04:30:23 +0000

If you’re getting occasional succesful pings but with droppped packets try using a higher Time To Live value in the Ping command (type Ping on its own and hit return to see all the switches available) as it sounds like there is a problem with the lines somewhere. As some one else has suggested Tracert (or Pathping) will let you see the route that the packets are taking and identify the slow link.

By: xevier

xevier — Thu, 26 May 2005 03:03:58 +0000

thanks all,
first i am sory for the pc question i included with this one.

as far as tracert is concerned, as it is our client we are having a direct connection through a serial port in router to the customer, so when i try tracert it reaches upto my router only.

as asked by bob,

1)i have checked for line errors . i also took loop from the customer end(as telephone company does),and observed it for more than 20 mins continously, it was fine.the telephone company says as the loop was fine there was no error in the line.

2)also the line is up all the time(shown in router) but no ping.and the customer is not able to browse the Internet.

3)we are having fibre in between with HDSL lines.

4)the router at the customer end is maintained by nontechies,so i don’t suspect that they would have dared to change any configuration.

can you tell me Dargandk how to create virtual interface and how to use it.
i think it must be something in network layer but we have made no changes in the configuration.i am not able to understand what has happened.

please help

By: bobkberg

bobkberg — Wed, 25 May 2005 11:32:18 +0000

Have you checked the router stats for line errors and such?

You say that you’ve been trying to ping to the customer end, and to a Windows PC. Would you please expand on that?

What does the problem look like from the customer’s point of view? – or is there onem meaning does the customer have a problem, or is this only visible to you?

Who controls the router at the customer end?

Have you checked with your phone company to see what stats are visible from their point of view?

You mentioned V.35, but not the actual transport mechanism – Some form of DSL I’d guess because of the Lecar modem.

Another thing to check (if DSL) is whether or not anyone has added unfiltered equipment to the phone line in question. I recall one of my customers where it turned out that the alarm company had connected their equipment to the customer’s DSL line, without permission and unfiltered to boot!

Others have already commented on the IP characteristics, but the heavy loss you’re describing sounds more like line trouble to my ears.

Bob

By: carlositurrioz

carlositurrioz — Wed, 25 May 2005 10:05:05 +0000

Like john said, sounds like a Internet protocol is blocked, try to use some sniffer to trace the net traffic or if you have some packeteer or somethign similar

By: dargandk

dargandk — Wed, 25 May 2005 09:46:58 +0000

Some Obvious things to check would be

A- Routing , making sure that destination router has route back to orignating router.

B- Second option would be to check the access list to block pings. Sometime the pings are blocked to the interface itself. You may want to create a virtual interface and then try the ping test

Hope it helps

Dharminder Dargan

By: xevier

xevier — Wed, 25 May 2005 07:48:01 +0000

it was working fine till the day before,from two days it is causing problem.also i can get pinging but with packet loss i.e. 1-2 pinging after 10-12 Request timed out.if it were access-list or something in the configuration it shouldnot have ping even once???
any help?