Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. If you'd prefer to explore, try our test area to get started. And see here for current known issues.

New Member

Packets Larger Than Fragmentation Size Get Dropped in FR

Hello, if anyone can help me with this issue, then i would greately appreciate it.

I have 3 offices with FR links through my ISP MPLS networks. The central office has 1536 kbps link and the other 2 remote offices each has a 512 kbps link.

I am doing VoIP over the FR links with policy-based fragmentation on the subinterface. I configured the fragmentation size to be 640 bytes (the recommended size for 512 link) for each FR link. The central office also has the fragmentation size of 640 bytes even though it has a 1536 kbps link because i needed to keep the fragmentations size consistent with all my FR links.

The problem is when sending packets that are larger than the fragmentation size (>640 bytes), the packets get dropped. When i removed the fragmentation configuration, then everything works fine.

Does anyone have any idea how i can configure fragmentation correctly on FR links? Any help is appreciated. Thanks.



Here is a partial sample of my config.

class-map match-all VoIP_Traffic

match access-group name Voice_Traffic

class-map match-all VoIP_Signalling

match access-group name Voice_Signalling



policy-map VoIP_Priority

class VoIP_Signalling

bandwidth 8

class VoIP_Traffic

priority 500

class class-default


random-detect dscp-based

interface Serial0/0/0

description <<Link to NVPN Networks>>

no ip address

no ip redirects

no ip unreachables

no ip proxy-arp

encapsulation frame-relay IETF

no ip mroute-cache

load-interval 30

no fair-queue

service-module t1 timeslots 1-8

frame-relay traffic-shaping

frame-relay lmi-type ansi


interface Serial0/0/0.1 point-to-point

description <<Point-to-Point FR>>

bandwidth 512

ip address

frame-relay interface-dlci 123

class VOIPovFR

map-class frame-relay VOIPovFR

frame-relay fragment 640

frame-relay cir 512000

frame-relay bc 5120

frame-relay be 0

frame-relay mincir 512000

service-policy output VoIP_Priority


Re: Packets Larger Than Fragmentation Size Get Dropped in FR