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PPPoE MTU and fragmentation

Hello all

We have subscribers having issues on one of our aggregation routers (asr9001) that sound like MTU problems but I can't seem to work out how to fix them - any pointers would be greatly appreciated.


We are trying to use an MTU of 1492, does the following look OK? I don't understand why there is fragmentation at this MTU value



pppoe bba-group PPPoE-BBA-Link2
mtu 1492
sessions mac limit 1
control-packets priority 0


arp scale-mode-enable
pta tcp mss-adjust 1452


type ppp PPPOE_TPL
ppp authentication pap chap
keepalive 60 5
ppp mru ignore
ppp ipcp dns
ppp ipcp peer-address pool WAN_IPv4_PRIVATE_POOL
accounting aaa list default type session periodic-interval 5 dual-stack-delay 5
ipv4 mtu 1492
ipv4 verify unicast source reachable-via rx
ipv4 unnumbered Loopback1
ipv4 unreachables disable
ipv4 access-group subscriber_acl_out egress


interface Bundle-Ether20
description Link #2 aggregation bundle
mtu 1600
service-policy output WAN-OUT
ipv4 tcp-mss-adjust enable
ipv6 enable
lacp mode active
interface Bundle-Ether20.0
service-policy output egress subscriber-parent resource-id 0
ipv4 tcp-mss-adjust enable
ipv6 tcp-mss-adjust enable
service-policy type control subscriber PPP_PM
pppoe enable bba-group PPPoE-BBA-Link2
bundle load-balancing hash dst-ip
encapsulation ambiguous dot1q 3000-3227 second-dot1q any


The following counter is always increasing

RP/0/RSP0/CPU0:EQ-ASR-9001-NBN#sh contr np counters np0 location 0/0/CPU0 | i FRAG
Tue Apr 28 10:11:54.644 AEST
1050 PUNT_PPPOE_FRAG_NEEDED 434132510 1001
1051 PUNT_PPPOE_FRAG_NEEDED_EXCD 174290821 317


An example subscriber

RP/0/RSP0/CPU0:EQ-ASR-9001-NBN#show im database interface BE20.0.pppoe1775
Tue Apr 28 10:14:37.724 AEST

View: OWN - Owner, L3P - Local 3rd Party, G3P - Global 3rd Party, LDP - Local Data Plane
GDP - Global Data Plane, RED - Redundancy, UL - UL

Node 0/RSP0/CPU0 (0x1)

Interface Bundle-Ether20.0.pppoe1775, ifh 0x007451a0 (up, 1500)
Interface flags: 0x0000000000220847 (SUBSCRIBER|REPLICATED
Encapsulation: ppp
Interface type: IFT_PPPOE
Control parent: Bundle-Ether20.0
Data parent: Bundle-Ether20.0
Views: UL|G3P|L3P|OWN

Protocol Caps (state, mtu)
-------- -----------------
None qos_out (up, 1500)
None ppp (up, 1500)
ipv4 ipcp (up, 1492)
ipv4 ipv4 (up, 1492)
ipv4 ipv4_acl_out (up, 1472)



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