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Lost Fragments Multilink PPP

Dear Experts,

Good Morning,

I am getting lot of lost discards on my T1 link. Its a SPA-2X-T3/DS0 card which is channelized to T1 and bundled to a multilink,What might be the reason for lost fragments ?

Please find the output below:

Multilink1, bundle name is TESTING
  Bundle up for 12w6d
  Bundle is Distributed
  7733426 lost fragments, 0 reordered, 0 unassigned
  0 discarded, 0 lost received, 85/255 load
  received sequence unavailable, 0xB511 sent sequence
  Member links: 2 active, 0 inactive (max not set, min not set)
    Se3/0/0/5:0, since 12w6d, no frags rcvd
    Se3/0/0/7:0, since 3w0d, no frags rcvd
  Distributed fragmentation on. Fragment size 512.  Multilink in Hardware.

7733426 lost fragments

Warm Regards,

Pramod

1 REPLY
Hall of Fame Super Silver

Re: Lost Fragments Multilink PPP

Hello Pramod,

hardware based fragmentation is supported only if the MLPPP has only one member according to SIP and SPA configuration guide

http://www.cisco.com/en/US/docs/interfaces_modules/shared_port_adapters/configuration/6500series/76cfgct3.html#wp1168724

Hardware MLPPP LFI Guidelines

LFI using MLPPP will function only in hardware if there is just one  member link in the MLPPP bundle. The link can be a fractional T1 or full  T1. Note the following guidelines:

The ppp  multilink interleave command must be configured to enable  interleaving.

Only three fragmentation sizes  are supported: 128 bytes, 256 bytes, and 512 bytes.

Fragmentation is enabled by  default, and the default size is 512 bytes.

A policy map having a priority  class must be applied to the main interface.

When hardware-based LFI is  enabled, fragmentation counters are not displayed.

in your case we see that there two members that are two T1 derived from the same channelized T3 port.

Member links: 2 active, 0 inactive (max not set, min not set)
     Se3/0/0/5:0, since 12w6d, no frags rcvd
    Se3/0/0/7:0, since 3w0d,  no frags rcvd

the show provides information that is in contrast:

7733426 lost fragments

but no frags received on member link, meaning other side is not fragmenting, so where are lost these fragments in sending?

in your case using two member links LFI is software based on the SPA and this can be the cause of lost fragments but I have some doubts if the counters are real or not. Are you experiencing a real issue?

An FTP file transfer performs poorly over the bundle?

>> Distributed fragmentation on. Fragment size 512.  Multilink in Hardware.

Hope to help

Giuseppe

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