VLAN tag. When it is taken out?

VLAN tag. When it is take out?

I have a question related with the tag which it's inserted in the Layer-2 frame. What happens when an equipment which doesn't implement 802.1q get a packet whit his mac address as destination address?

For example, there is a switch with the port Fa0/1 configured with a VLAN with vlan-id=1. And there is the port Fa0/2 which is in trunk mode and connected to a router which is the LAN's gateway. When the equipment that is connected at Fa0/1 send a package to the somewhere out of the LAN, the package when it goes out from Fa0/2, It has the TAG? or the F0/2 as it is a mode trunk take out the tag? where the tag is taking out? if it's take out. Thats my question.



If ones of that IP phone which are configure with vlan-id=7. send a package to a sip server out of the LAN. When the packages goes out from the switch by port Fa0/1 (which it's in trunk mode). It take out the tag? The tag will arrive to the sip server with the tag?

Regards.

Re: VLAN tag. When it is take out?

I think it depends on whether the LAN gateway supports 1522 byte frames or not. One that only supports 1518 byte (untagged) frames will probably report an error and not pass the frame at all. Ones that do support 1522 byte frames will pass the tag unchanged. I'm not sure but I would guess it isn't possible to strip out the tag information and pass the remainder of a frame onwards or misinterpret the tag field as part of something else.

There is a good reference to the mechanism here:


Brian.

Re: VLAN tag. When it is take out?

Thank you for you reply betwixt. But, the switch and router that are implemented in the network which I attached the image before, use actual version (so it take care 802.1q). So as the frame is in the network there is not problem, the switch and the router treat the VLANs by what it's configure in them. But the connection between the border routers, thats which connects the core network with the ISP (internet services provider). What happends there? or the ISP has to treat the VLANs as the ower core network do or the border router has to take out the tag. I think that the ISP would like to use his rules to treat the clients as they want. so I don't know what happends there.

Re: VLAN tag. When it is take out?

Well for what I'm seeing the router or every L3 equipment take out the VLAN tag. That's because when a package arrives, the router steps are:

1: see if the mac address destination is the own address or the broadcast address. If the destination address is not, the frame is eliminated.
2: Look the CRC

And that is just what a router see in the ethernet layer.

3: Take out Ethernet frame and just use the IP frame, seeing first the TTL and all that stuff.
4: See the ip destination and compare it with the router table, if the destination network is not in the router table the router eliminates the package and if it is, the router creates the new IP frame and send it encapsulating it in a new MAC frame (IEEE 802.3)

To keep the VLAN tag in the ethernet frame it necessary to use inter VLAN routing.

Re: VLAN tag. When it is take out?

That is my understanding too. The tag only exists within a LAN and is never imported or exported to a WAN. If it went outside the LAN, it's number could no longer be used to identify an end point anyway.

Brian.