04-14-2021 12:49 PM
Hi Cisco people,
I've just inherited a Cisco L2 device running IOS XR 6.6.12. This switch has a bundle connection to another identical switch. I see this subinterface on the switch-to-switch bundle connection in the running config:
interface Bundle-Ether3.1000 l2transport description vlan 1000 to other switch encapsulation dot1q 1000 second-dot1q 123
I understand enough to know that the the above allows all traffic tagged with VLAN 1000 across the Bundle. Easy enough. But what is that "second-dot1q" VLAN 123? Is that a double-tagged VLAN? The "?" menu isn't much help:
RP/0/RP0/CPU0:SW-1#conf t RP/0/RP0/CPU0:SW-1(config)#interface Bundle-Ether3.1000 l2transport RP/0/RP0/CPU0:SW-1(config-subif)#encapsulation dot1q 1000 ? , <comma> exact Do not allow further inner tags ingress Perform MAC-based matching second-dot1q IEEE 802.1Q VLAN-tagged packets <cr> RP/0/RP0/CPU0:SW-1(config-subif)#encapsulation dot1q 1000
I'm not a Layer 2 guy, so I'm not sure what "IEEE 802.1Q VLAN-tagged packets" could mean here. What is VLAN 123's relationship to VLAN 1000 in my example? What traffic will be permitted across the bundle with this config? Thank you!
Solved! Go to Solution.
04-14-2021 01:01 PM
The second tag is for Q-in-Q vlan traffic.
see link below for more info:
https://www.cisco.com/en/US/docs/ios/lanswitch/configuration/guide/lsw_ieee_802.1q.html
HTH
04-14-2021 01:01 PM
The second tag is for Q-in-Q vlan traffic.
see link below for more info:
https://www.cisco.com/en/US/docs/ios/lanswitch/configuration/guide/lsw_ieee_802.1q.html
HTH
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