MTU size for PPPOE with QinQ

[anas.abdullkarim]

i have router asr1006 , i used at as A pppoe server i have used QINQ secend tag in rotuer

interface TenGigabitEthernet2/0/0.904
 description Cust1-QINQ
 encapsulation dot1Q 904 second-dot1q any
 pppoe enable group PPPOE-SERVER3



interface Virtual-Template2
 **mtu 1492**
 ip unnumbered Loopback0
 ip nat inside
 no logging event link-status
 peer default ip address pool interface localpool2
 keepalive 15
 ppp mtu adaptive
 ppp authentication chap ms-chap ms-chap-v2 eap pap
 ppp ipcp dns 8.8.8.8 8.8.4.4
 ppp timeout idle 172800 either
end

the used is connected but they have some website not open and some application not working too i think the issue with MTU because i used double tag (qinq) so what MTU size must be ?

[Joseph W. Doherty]

I recall any and all VLAN tagging (including Q in Q) extends the frame size, so MTU shouldn't need to be adjusted.

[anas.abdullkarim]

hello , my client have many issues , like website not open ,like dns issues , and upload is too slow

[Giuseppe Larosa]

Hello @anas.abdullkarim ,

try to use a reduced MTU like  1484 to take in account  two 802.1Q Vlan tags.

I agree the symptoms are compatible with MTU issues that cause fragmentation that is the real problem.

Hope to help

Giuseppe

[anas.abdullkarim]

ok , i will try
about tcp mss ? not change it ?

[Giuseppe Larosa]

Hello @anas.abdullkarim ,

you can reduce by 8 also the TCP MSS to 1844 bytes

Hope to help

Giuseppe