multiple VLANs assigned to a server/workstation port

[dburd]

Yes this subject has been raised before - many times. But Dell's PowerConnect switches seem to contradict what so many have said is not possible, that one server/workstation can communicate with multiple VLANs using a non 802.1Q compliant NIC nor operating system - using an *untagged* port on their switch. and no L3 routing.

For any given interface on a Dell 33xx: "General mode allows the administrator to configure multiple VLANs that can be either tagged or untagged; this is useful for nodes that must communicate on more than one VLAN." Whole 6 page PDF here: http://www.dell.com/downloads/global/products/pwcnt/en/app_note_8.pdf

does this not contradict what I have read so many times in this forum and CISCO documentation? (Cisco allows multiple VLANs on a tagged port, for communications with an 802.1Q compliant switch, router or NIC.) Maybe this is a Dell only 'feature'? It seems that this 'feature', while not part of 802.1Q rfc, is what many companies want. though i don't want a dell switch.

[tbaranski]

I've never heard anyone say that multiple untagged VLANs on a port isn't possible. It's extremely uncommon in the world of Cisco because Cisco hasn't implemented some features that are frequently seen from other vendors, but it's certainly possible via a number of methods.

The easiest way is just to treat a port as if it's always in multiple VLANs; i.e., allow all member VLANs to send traffic to the port and allow hosts on the port to send traffic to all member VLANs. So on a per-packet basis there's no VLAN classification: each packet is treated as if it's potentially a member of any member VLAN.

Other ways include classifying traffic into a VLAN based on identifiers other than VLAN tags, such as layer-2 or layer-3 addresses. For example, a packet entering a port which is a member of multiple VLANs can be dynamically assigned to the appropriate VLAN based on it's source MAC or IP address.

So there are a lot of options, and I don't why Cisco has yet to implement any of these (sometimes useful but usually ugly) features.