Anyone encountered Cisco ATM PVC large delay bug?
Hi nanog, I'm not sure how many percentage of global NSP/ISP use ATM PVC to provide links between their Cisco routers. It seems there is some large delay bugs in Cisco ATM interface, esp on GSR level routers. In more detail, our situation is: if we get a high bandwidth PVC, say 51M(or 80M), and if the bandwidth utilization reaches 80% percent, the ATM link will encounter a 1500~2000 ms delay - just point to point ping across the link. We have found this situation is associated with "sar txpool" setting in Cisco GSR, and a manipulation of the "sar txpool" together with bandwidth increasing has solved the problem now. But I still wonder if any of you ever encounter this situation(bug), and how did you overcome it? If you are still puzzled by this bug, I'd like share our temp solution with you. regards, Yu Ning ------------------------------------------- (Mr.) Yu Ning ChinaNet Backbone Operation Networking Dep.,Datacom Bureau China Telecom.,Beijing(100088),P.R.C +86-10-66418121/66418122/66418123(fax) -------------------------------------------
Are you accounting for ATM overhead? Remember, the sho in bits/sec do NOT count overhead (another words, they are looking at true bits/sec, not cells/sec). You should check cells/sec on the ATM port you are connected to.
In more detail, our situation is: if we get a high bandwidth PVC, say 51M(or 80M), and if the bandwidth utilization reaches 80% percent, the ATM link will encounter a 1500~2000 ms delay - just point to point ping across the link. We have found this situation is associated with "sar txpool" setting in Cisco GSR, and a manipulation of the "sar txpool" together with bandwidth increasing has solved the problem now.
But I still wonder if any of you ever encounter this situation(bug), and how did you overcome it? If you are still puzzled by this bug, I'd like share our temp solution with you.
regards,
Yu Ning
------------------------------------------- (Mr.) Yu Ning ChinaNet Backbone Operation Networking Dep.,Datacom Bureau China Telecom.,Beijing(100088),P.R.C +86-10-66418121/66418122/66418123(fax) -------------------------------------------
Hi, ----- Original Message ----- From: Alex Rubenstein <alex@nac.net> To: Yu Ning <yuning@cndata.com> Cc: nanog-post <nanog@merit.edu> Sent: Friday, April 21, 2000 8:01 AM Subject: Re: Anyone encountered Cisco ATM PVC large delay bug?
Are you accounting for ATM overhead? Remember, the sho in bits/sec do NOT count overhead (another words, they are looking at true bits/sec, not cells/sec).
You should check cells/sec on the ATM port you are connected to.
Yes. I get the utilization statistic from ATM PVC statistic.
In more detail, our situation is: if we get a high bandwidth PVC, say 51M(or 80M), and if the bandwidth utilization reaches 80% percent, the ATM link will encounter a 1500~2000 ms delay - just point to point ping across the link. We have found this situation is associated with "sar txpool" setting in Cisco GSR, and a manipulation of the "sar txpool" together with bandwidth increasing has solved the problem now.
But I still wonder if any of you ever encounter this situation(bug), and how did you overcome it? If you are still puzzled by this bug, I'd like share our temp solution with you.
regards,
Yu Ning
------------------------------------------- (Mr.) Yu Ning ChinaNet Backbone Operation Networking Dep.,Datacom Bureau China Telecom.,Beijing(100088),P.R.C +86-10-66418121/66418122/66418123(fax) -------------------------------------------
I think, the clue is in your accounting - you have 100% used bandwidth when you propose 80%. ATM bandwidth is a pretty twisted thing. If so, some queueries appear and it explain the delays. ----- Original Message ----- From: "Yu Ning" <yuning@cndata.com> To: "Alex Rubenstein" <alex@nac.net> Cc: "nanog-post" <nanog@merit.edu> Sent: Thursday, April 20, 2000 5:06 PM Subject: Re: Anyone encountered Cisco ATM PVC large delay bug?
Hi,
----- Original Message ----- From: Alex Rubenstein <alex@nac.net> To: Yu Ning <yuning@cndata.com> Cc: nanog-post <nanog@merit.edu> Sent: Friday, April 21, 2000 8:01 AM Subject: Re: Anyone encountered Cisco ATM PVC large delay bug?
Are you accounting for ATM overhead? Remember, the sho in bits/sec do NOT count overhead (another words, they are looking at true bits/sec, not cells/sec).
You should check cells/sec on the ATM port you are connected to.
Yes. I get the utilization statistic from ATM PVC statistic.
In more detail, our situation is: if we get a high bandwidth PVC, say 51M(or 80M), and if the bandwidth utilization reaches 80% percent, the ATM link will encounter a 1500~2000 ms delay - just point to point ping across the link. We have found this situation is associated with "sar txpool" setting in Cisco GSR, and a manipulation of the "sar txpool" together with bandwidth increasing has solved the problem now.
But I still wonder if any of you ever encounter this situation(bug), and how did you overcome it? If you are still puzzled by this bug, I'd like share our temp solution with you.
regards,
Yu Ning
------------------------------------------- (Mr.) Yu Ning ChinaNet Backbone Operation Networking Dep.,Datacom Bureau China Telecom.,Beijing(100088),P.R.C +86-10-66418121/66418122/66418123(fax) -------------------------------------------
participants (3)
-
Alex Rubenstein -
Alexei Roudnev -
Yu Ning