This article specifies the limitation of the " no-fragmentation " knob on a channelized LSQ interface in MX and M Series routers.

LFI (Link Fragmentation and Interleaving) reduces excessive delays by fragmenting large packets into smaller packets and interleaving them with real-time frames. This allows real-time and non-real-time data frames to be carried together on lower-speed links, without causing excessive delays to the real-time traffic.

Users will get a commit error while mapping the forwarding-map (configured with no-fragmentation) to a channelized LSQ interface.

set class-of-service fragmentation-maps FRAGMENT forwarding-class h1 no-fragmentation

{MASTER}[edit]
labroot@jtac-mx104-r2008# set class-of-service interfaces lsq-0/0/0:2 unit 500 fragmentation-map FRAGMENT

[edit]
MX104# commit check
[edit class-of-service interfaces lsq-0/0/0:2 unit 500 fragmentation-map]
  'fragmentation-map FRAGMENT'
    Fragmentation-map FRAGMENT invalid for lsq-0/0/0:2.500 (FC-to-LFI mapping not applicable)
error: configuration check-out failed

This behavior is by design. "no-fragmentation" is not supported on channelized LSQ units. The fragmentation map, which contains any of the forwarding classes mapped to the LFI, is not allowed.