Will my QINQ configuration work ?

[yann.boulet]

Hi all,

I would like to use QINQ on my metro network, I have 2 sites A and B, on A side the EDGE switch support dot1q-tunnel on the B side the EDGE switch doesnt't support dot1q-tunnel. so here is what I want to do, can you please tell me if it will work :

A SIDE : CUSTOMER SWITCH WITH VLAN DOMAIN

A SIDE : CUSTOMER CONNECTED TO MY EDGE SWITCH THAT SUPPORT QINQ WITH A TRUNK and DOT1Q-TUNNEL (VLAN 300)

BETWEEN A and B : L2 LINK

B SIDE : MY EDGE SWITCH THAT DOESN'T SUPPORT QINQ CONFIGURED WITH TRUNK AND VLAN 300

B SIDE : MY SWITCH THAT SUPPORT QINQ WITH TRUNK FROM EDGE SWITCH AND DOT1Q-TUNNEL (VLAN300 TERMINATION) TO CUSTOMER B SIDE SWITCH

B SIDE : CUSTOMER SWITCH WITH VLAN DOMAIN

I know that double tagged ethernet frames are differents so I want to know if my Edge switch on B side will switch double tagged packets ?

thanks

[Giuseppe Larosa]

Hello Yann,

the proposed setup can work, but all of your switches have to be configured for a bigger MTU because QinQ adds a 4 byte overhead. The switch in the middle has only to switch frames with external Vlan tag 300 between two trunk ports.

Native Vlan in all trunk links must be different then Vlan 300 to avoid to expose client Vlans.

Hope to help

Giuseppe

[yann.boulet]

Thank you giuslar,

can you give me some configuration example, it means that I only have to increase MTU on the switch that doesn't support DOT1Q-TUNNEL ?

thanks

[Giuseppe Larosa]

Hello Yann,

you have to increase the MTU on all of your devices as all of them have to handle double tagged frames not only in the switch in the middle.

In low end devices you may need to increase the system MTU and you are not allowed to increase the MTU only on specific interfaces.

Read this chapter from C3560 configuration guide

http://www.cisco.com/en/US/docs/switches/lan/catalyst3560/software/release/12.2_58_se/configuration/guide/swtunnel.html

System MTU

The default system MTU for traffic on the switch is 1500 bytes. You can  configure Fast Ethernet ports to support frames larger than 1500 bytes  by using the system mtu global configuration command. You can configure Gigabit Ethernet ports to support frames larger than 1500 bytes by using the system mtu jumbo global  configuration command. Because the IEEE 802.1Q tunneling feature  increases the frame size by 4 bytes when the metro tag is added, you  must configure all switches in the service-provider network to be able  to process maximum frames by increasing the switch system MTU size to at  least 1504 bytes. The maximum allowable system MTU for Gigabit Ethernet  interfaces is 9000 bytes; the maximum system MTU for Fast Ethernet  interfaces is 1998 bytes.

Hope to help

Giuseppe