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Misconfiguring LFI on LSQ interface causes MLPPP connectivity loss

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Article ID: KB23545 KB Last Updated: 20 Jun 2013Version: 3.0
Summary:
This article describes the behavior of a misconfigured LFI with the MLPPP on M120.

Symptoms:
After migrating the MLPPP circuit with CE from M20 to M120, the connection was lost.

Environment:
  • LS- (Link Service PIC) was used on the M20.
  • LSQ- (AS2 Layer-2 Services PIC) was used on M120.
  • CE is a Cisco router.

Command output:

> show interfaces terse
Interface                      Admin       Link        Proto        Local            Remote
......
ce1-1/2/7                     up            up
ds-1/2/7:1                    up            up
ds-1/2/7:1.0                  up            down       mlppp        lsq-1/3/0.2
.....
lsq-1/3/0                     up            up
lsq-1/3/0.2                   up            down       inet         202.160.194.189/30


> show log messages | match ppp
Apr 9 14:50:30 m120-re0 /kernel: if_pfe_mlppp_ifl_config lsq-1/3/0: ifl config: op: 2; sub: 2; flags: 0x8010, curr: 0xc010. rlsq 0
Apr 9 14:50:30 m120-re0 /kernel: [mlppp] ds-1/2/7:1.0 of lsq-1/3/0.2 is down
Apr 9 14:50:30 m120-re0 /kernel: [mlppp] ds-1/2/7:1.0 leaves lsq-1/3/0.2
Apr 9 14:50:30 m120-re0 /kernel: [mlppp] lsq-1/3/0.2 reset remote MRRU to N/A
Apr 9 14:50:30 m120-re0 /kernel: [mlppp] reset lsq-1/3/0.2 family MTUs to configured value

Cause:

After troubleshooting, it was determined that the LFI with the MLPPP on M120 was misconfigured.

The MLPPP configuration of the working M20 was compared with the MLPPP configuration on M120:


MLPPP configuration on M120:

> show configuration interfaces lsq-1/3/0 unit 2
encapsulation multilink-ppp;
mrru 1524;
fragment-threshold 128;
minimum-links 1;
multilink-max-classes 4;
......

> show configuration class-of-service interfaces lsq-1/3/0 unit 2
scheduler-map aaa_00007636BKK_Scheduler-Map;
fragmentation-map aaa-TEST;
shaping-rate 256k;

> show configuration class-of-service fragmentation-maps aaa-TEST
forwarding-class {
   premiumrt {
      fragment-threshold 128;
      multilink-class 2;
   }
   standard {
      fragment-threshold 128;
      multilink-class 0;
   }
   business {
      multilink-class 1;
   }
   nc_premiumnrt {
      fragment-threshold 128;
      multilink-class 3;
   }
}



MLPPP configuration on M20 which was working:

> show configuration interfaces ls-0/0/0 unit 2
encapsulation multilink-ppp;
mrru 1524;
fragment-threshold 128;
interleave-fragments;


"interleave-fragments" is NOT valid on LSQ-,  to remove MCML from M120, just enabled LFI as below while keeping the CE configuration unchanged.

> show configuration interfaces lsq-1/3/0 unit 2
encapsulation multilink-ppp;
mrru 1524;
fragment-threshold 128;
minimum-links 1;              # “multilink-max-classes” was removed
......

> show configuration class-of-service interfaces lsq-1/3/0 unit 2
scheduler-map aaa_00007636BKK_Scheduler-Map;
fragmentation-map aaa-TEST;
shaping-rate 256k;

> show configuration class-of-service fragmentation-maps aaa-TEST
forwarding-class {
   premiumrt {
      no-fragmentation;   # “multilink-class” option was set to use "no-fragmentation" option to make the voice traffic in this queue become LFI packets, while keep the packets in other queue to be fragmented into 128 Bytes
   }
}

Solution:

Conclusion:
When comparing, it was concluded that the CE was using LFI with MLPPP, NOT Multi-class MLPPP.  Whereas customer enabled MCML on the M120, which caused the LCP negotiation between M120 and CE to fail.

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