[c-nsp] [nsp] Strange multilink ppp issue with T1s
Bill Wichers
billw at waveform.net
Thu Jul 29 17:01:40 EDT 2004
Below is my posting again from June 11. Usually a reload of the router
will correct the issue for a time (which seems to vary somewhat), at which
point it starts dropping packets again. We see delayed packets as well as
dropped packets, the delays usually being about 100-200 ms while normal
RTTs are in the 3-5 ms range. The problem seems to be unrelated to loading
on the link.
-Bill
---- snip 8< ----
We have three T1 circuits on one end (a 7507) going into a PA-MC-4T1 in a
vip2-40, the other end consists of three channels on a DS3 in a PC-MC-2T3+
on another vip2-40 in one side of a 7576. Both routers have RSP4's running
IOS v12.2(6a).
What we are seeing is the the multilink bundle has large levels of packet
loss at times, and at other times none -- but all three T1 circuits are
clean at all times. The link seems to have unpredictable lag (and behaves
especially poorly in packet lag and loss when loaded) regardless of the
settings for fragmentation. The strangest part is that the 7507 end sees
the circuit frequently moving far more traffic than the bundles max
capacity of 4.6 Mb/s, while the other end sees more believeable traffic
numbers. The available bandwidth is reported correctly on both ends. I
included results of 'show ppp multilink' and 'show multilink1' for each
end. And we have tried the 7507 both with distributed CEF and without. No
difference... Fragmentation is disabled on both ends at the moment (and in
the 'show' info below).
Really hoping someone can provide a bit of insight since we can't seem to
find any info on this anywhere and have tried everything we can think of
to fix it.
-Bill
[7507 begin]
troy1>show int multilink1
Multilink1 is up, line protocol is up
Hardware is multilink group interface
Internet address is x.x.x.x/30
MTU 1500 bytes, BW 4608 Kbit, DLY 100000 usec,
reliability 255/255, txload 27/255, rxload 135/255
Encapsulation PPP, loopback not set
Keepalive set (10 sec)
DTR is pulsed for 2 seconds on reset
LCP Open, multilink Open
Open: IPCP
Last input 00:00:00, output never, output hang never
Last clearing of "show interface" counters 4w3d
Queueing strategy: fifo
Output queue 0/40, 2069415 drops; input queue 0/75, 396 drops
30 second input rate 2442000 bits/sec, 654 packets/sec
30 second output rate 5698000 bits/sec, 1018 packets/sec
692034835 packets input, 3061367520 bytes, 0 no buffer
Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
1017262671 packets output, 1171349294 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets
0 output buffer failures, 458140128 output buffers swapped out
0 carrier transitions
troy1>
troy1>show ppp multilink
Multilink1, bundle name is sfld2core1
Bundle up for 3w0d
118828 lost fragments, 43010323 reordered, 5 unassigned
120023 discarded, 120023 lost received, 1/255 load
0x534FDF received sequence, 0x192D02 sent sequence
Member links: 3 active, 0 inactive (max not set, min not set)
Serial4/0/1:0, since 3w0d, last rcvd seq 534FE7
Serial4/0/2:0, since 3w0d, last rcvd seq 534FDF
Serial4/0/0:0, since 1w2d, last rcvd seq 534FE6
[7507 end]
[7576 begin]
sfld2core1>show int multilink1
Multilink1 is up, line protocol is up
Hardware is multilink group interface
Internet address is y.y.y.y/30
MTU 1500 bytes, BW 4608 Kbit, DLY 100000 usec,
reliability 255/255, txload 4/255, rxload 164/255
Encapsulation PPP, loopback not set
Keepalive set (10 sec)
DTR is pulsed for 2 seconds on reset
LCP Open, multilink Open
Open: IPCP
Last input 00:00:02, output never, output hang never
Last clearing of "show interface" counters 3w0d
Queueing strategy: fifo
Output queue 0/40, 0 drops; input queue 0/75, 5 drops
30 second input rate 2972000 bits/sec, 587 packets/sec
30 second output rate 86000 bits/sec, 128 packets/sec
335627760 packets input, 2579977254 bytes, 0 no buffer
Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
124442011 packets output, 1807068880 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets
0 output buffer failures, 0 output buffers swapped out
0 carrier transitions
sfld2core1>
sfld2core1>show ppp multilink
Multilink1, bundle name is troy1
Bundle up for 3w0d
Bundle is Distributed
5318 lost fragments, 3944230 reordered, 0 unassigned
441 discarded, 441 lost received, 84/255 load
0x193A1C received sequence, 0x555F07 sent sequence
Member links: 3 active, 0 inactive (max not set, min not set)
Serial1/0/0/25:0, since 3w0d, no frags rcvd
Serial1/0/0/24:0, since 3w0d, no frags rcvd
Serial1/0/0/26:0, since 1w0d, no frags rcvd
[7576 end]
> Can you ask the question again for me?
>
> What platform?
> What code?
> What problem?
>
> Thanks,
> Rodney
>
> On Thu, Jul 29, 2004 at 01:56:18PM -0400, Bill Wichers wrote:
>> I'm assuming you are referring to my post from some time back.
>> Unfortunatly, no, I have not found any solutions to the problem and I've
>> tried just about everything I can find info on. This seems to be a big
>> stumper -- I didn't even get any responses here :-(
>>
>> Our ultimate solution was to cheat and order a DS3 with has the added
>> advantage of being faster too... Since there is already fiber in the
>> building, and the other end is our facility in a CO, this was a
>> reasonable
>> (although more expensive) option for us. I would still like info on the
>> MPP issue since we do have some POPs still fed this way, but for
>> whatever
>> reason the problem doesn't seem to have as much effect on 2 T1 bundles
>> as
>> bundles with 3 or more.
>>
>> -Bill
>>
>> > Did you every find a solution to this problem? I have a problem that
>> is
>> > very very similar. Thanks in advance.
>> >
>> >
>> >
>> > John
>> >
>> *****************************
>> Waveform Technology
>> UNIX Systems Administrator
>>
>>
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>
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