Thank you very much for your information. I get that page, and know it's for debugging reason. regards, Yu Ning -----Original Message----- From: Blake Fithen <fithen@NetworksPlus.com> To: 'Yu Ning' <yuning@cndata.com>; Dumb Kid <dumbkid0@yahoo.com>; nanog-post <nanog@merit.edu> Date: Thursday, May 11, 2000 10:07 AM Subject: RE: ??: Strange result while ping serial interface

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From the Cisco "System Management" document:

http://www.cisco.com/univercd/cc/td/doc/product/software/ssr90/tsc_r90/5401 9 .htm

"Note If the IP version of the ping command is used on a directly connected interface, the packet is sent out the interface and should be forwarded back to the router from the far end. The time travelled reflects this round trip route. This feature can be useful for diagnosing serial line problems. By placing the local or remote CSU/DSU into loopback mode and "pinging" your own interface, you can isolate the problem to the router or leased line."

blake

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-----Original Message----- From: Yu Ning [SMTP:yuning@cndata.com] Sent: Wednesday, May 10, 2000 9:00 PM To: Dumb Kid; nanog-post Subject: ??: Strange result while ping serial interface

Hi,

But it's obviously inefficient. Is it due to some inability of PPP ? Or can you tell what reason makes the packets a round trip ?

Since the router should have the information of its local interface, why should it always send packets out, the get it back ?

regards,

Yu Ning

-----Original Message----- From: Dumb Kid <dumbkid0@yahoo.com> To: Yu Ning <yuning@cndata.com>; nanog-post <nanog@merit.edu> Date: Thursday, May 11, 2000 9:45 AM Subject: Re: Strange result while ping serial interface

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Yeah , it's normal. The packet actually travels to the other end of the router over the serial and back. That's why the response time is doubled.

--- Yu Ning <yuning@cndata.com> wrote:

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Hi nanog,

Strange thing happens everyday. When I were troubleshooting yestoday, I found a ping to my local serial interface (no matter it's 155M POS, or 2M Serial interface) takes nearly twice delay compared with a ping to the remote side of the serial interrface ! When I trace to my local serial interface, I got the first hop to the remote end, then second hop back to my local interface !

For example, 202.97.2.1 is local serial interface, while 2.2 is remote side. A trace on 2.1 to 2.1 first go to 2.2, then back to 2.1. And this situation can be verified on both side.

Have you ever seen this situation ? Is it due to our misconfiguration? or it's sheerly a mis-display of result in Cisco box (can't believe it)

The background is: we're using ISIS as IGP, and utilized level-1/2 link.

thanks for any input.

regards,

Yu Ning ------------------------------------------- (Mr.) Yu(2) Ning(2) ChinaNet Backbone Operation Networking Dep.,Datacom Bureau China Telecom.,Beijing(100088),P.R.C +86-10-66418121/66418122/66418123(fax) -------------------------------------------

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-- D.U.M.B.K.I.D.

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