multilink ppp troubleshooting - serial interfaces

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Apr 3rd, 2008
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I have two serial t1's bonded for multilink PPP with Sprint on a 12.4 IOS 2811 (Sprint's PE is a Cisco router as well).


The symptoms we see are download speeds are 1.3Mbit and upload speeds are 3.0Mbit. If I shut one serial interface down and run the same test I get 1.2Mbit down/1.3Mbit up. If I bring that one back up and shut the other one down I get roughly 1.2Mbit down/1.2Mbit up - (during all these speed tests there is a little bit of traffic crossing, but they were all done within minutes of each other so there is no bursty traffic that could be skewing this). When both interfaces are up we regularly are seeing 1.3Mbit down and 2.8-3.0Mbit up. There are no physical layer issues on the T1 controllers (no code violations, slip seconds, errored seconds). There are no input/output errors on the multilink virtual interface, no drops, etc. Sprint verifies seeing similar results on their interfaces.


Has anyone ever seen this before? Any idea what could be causing such an issue.


The config of the serial and multilink interface are: (ip address changed)

interface Multilink1

ip address 1.2.3.4 255.255.255.252

ip nbar protocol-discovery

ip nat outside

load-interval 30

ppp multilink

ppp multilink interleave

ppp multilink group 1

ppp multilink multiclass

max-reserved-bandwidth 100

!


interface Serial0/2/0:0

no ip address

ip nbar protocol-discovery

encapsulation ppp

no fair-queue

ppp multilink

ppp multilink group 1

max-reserved-bandwidth 100

!

interface Serial0/2/1:0

no ip address

ip nbar protocol-discovery

encapsulation ppp

no fair-queue

ppp multilink

ppp multilink group 1

max-reserved-bandwidth 100


show ppp multilink (with the above config):

Multilink1, bundle name is sl-gw14-fw

Endpoint discriminator is sl-gw14-fw

Bundle up for 01:48:10, total bandwidth 3072, load 1/255

Receive buffer limit 24000 bytes, frag timeout 1000 ms

Interleaving disabled

0/0 fragments/bytes in reassembly list

90 lost fragments, 5073 reordered

0/0 discarded fragments/bytes, 0 lost received

0xC0A80 received sequence, 0x882F3 sent sequence

Member links: 2 active, 0 inactive (max not set, min not set)

Se0/2/0:0, since 01:48:10, 5760 weight, 1496 frag size

Se0/2/1:0, since 01:00:08, 5760 weight, 1496 frag size

No inactive multilink interfaces


NOTE: The ppp multilink interleave command was removed and the same symptoms occur, however show ppp multilink shows:

Multilink1, bundle name is sl-gw14-fw

Endpoint discriminator is sl-gw14-fw

Bundle up for 01:49:06, total bandwidth 3072, load 1/255

Receive buffer limit 24000 bytes, frag timeout 1000 ms

0/0 fragments/bytes in reassembly list

90 lost fragments, 5073 reordered

0/0 discarded fragments/bytes, 0 lost received

0xC0D91 received sequence, 0x88632 sent sequence

Member links: 2 active, 0 inactive (max not set, min not set)

Se0/2/0:0, since 01:49:06

Se0/2/1:0, since 01:01:04

No inactive multilink interfaces


also ppp multilink multiclass was removed with the same symptoms


'ppp multilink fragment disable' was added to the config with the same symptoms.


ideas? thanks in advance!


ray


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Edison Ortiz Thu, 04/03/2008 - 16:10
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I've seen that behavior before. The provider had to fix their MLPPP configuration. I recommend escalating this issue with the provider as your configuration looks fine.


HTH,


__


Edison.

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