ROAS Tag

[Hosam Hassan]

when i have 2 different vlans on a cisco switch . and the switch connected to a router and the router using the subinterface (ROAS). i know that the switch will add a tag on the trunk port .. i am a little bit confused if a router sub interfce can also add a tag when the frame went back from int gig0/0.10 of the router to the trunk port of the switch 

so my final question > can the router sub interfce add a 802.1q tag or just receive it from the switch trunk port and understand it but not tag it him self 

[Richard Burts · Accepted solution]

Yes. If the router is sending a frame out a subinterface to a vlan on a trunk the router does add the vlan tag to the frame.

The router is able to read a tag on an incoming Ethernet frame and to add a tag on an outgoing Ethernet frame.