Dell 6248 vlan settings and IP Helper assistance

Posted on 2010-08-24
Last Modified: 2012-05-10
I know there are a plethora of posts going over VLAN's - I just want to confirm I am doing everything right for my situation before I start configuring (I don't have a test environment to mimic live so it is difficult to test).

Dell 6248p - primary layer 3 device.
5x Netgear GS724TP

Currently the setup is pretty straight forward - the Netgears are all on VLAN2, which is set by the Dell...the ports linking the Netgear to the Dell are simply assigned to only VLAN2 as untagged.

What I am looking at into doing now is adding a Voice VLAN into the mix and breaking a few of the switches off onto another VLAN.  We are in an older building, so the line is currently being shared by both an Avaya IP Office VOIP system as well as the data, the phones are acting as a switch (Avaya 5602 and 5610's mainly).

The part I am a bit fuzzy on is for two parts:

the first is regarding the link going from the Netgear to the Dell.  Since the link port is going to be handling two VLAN's (at least one of them tagged) I know I need to change the Link Port from Access...but should I be changing it to General or Trunk?

the second goes along with the answer to the first - if using a Trunk port I then need to have all traffic Tagged, the voice channels will already be tagged by the phone but for the data VLAN, which is currently untagged, do I need to Tag is prior to it getting to the Dell (that being configuring the VLAN on the Netgear) or can it be tagged by the Dell?

The best case scenario for us is to keep as much, if not all, of the configuration changes on the Dell.  So if a Trunk port requires the traffic to be tagged before getting to the Dell, is it possible to use a 'General' port and keep the traffic untagged or tag it at the Dell?
I have IP Helper portion working now, leaving the below portion in but it is now irrelevant:
The second part of the question is regarding the IP Helper...i have the newer Firmware for the Dell which gets rid of DHCP relay and changes to IP Helper.  The part I am not sure on is if I can just use the following command which Dell CLI manual indicates "To relay DHCP packets received on any interface to DHCP server"

DHCP server location setup:
ip helper-address x.x.x.x dhcp

This appears to indicate I can do this one global command (while not under a VLAN, just at the config #) to enable IP Helper for the entire device...and realistically once that is set I am done (at least for DHCP relay)

Am I missing anything?
Question by:americaneldercare
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Accepted Solution

cdowdy earned 500 total points
ID: 33519641
Looks to me like you could use either, trunk or general.  The difference seems to be that the general port offers additional options including the ability to send more than one vlan untagged. In your case, this looks to be unnecessary as you do not seem to be using any protocols like LACP which require vlan 1 to be untagged as well, so you could just as easily use vlan 2 as your native on a trunk port and it will be the only untagged vlan.

Here is a pretty good document that explains the various commands on the dell:

That said - Personally, after reading Dell's doc, I might even try using the general port type as it seems interesting and provides some additional capability. I'll see if I can sum it up a bit:

Port type trunk - Here, you would be tagging all outgoing frames from the dell other than those in the vlan you configure as the native vlan. So, since you are currently using vlan 2 as your standard data vlan, and are not trunking on your netgear switches, you would want to go with native vlan 2. This config would look something like this:
(config)#interface ethernet g1
(config-if)#switchport mode trunk
(config-if)#switchport trunk allowed vlan 2,
(config-if)#switchport trunk native vlan 2

So, with the above, your voice vlan will be the only one tagged as it NOT the native vlan. The way this works is that outgoing frames that are from the native vlan (in this case vlan 2) are sent untagged and can connect right into an access port, such as the ports on your netgear switches. Incoming frames which show up untagged, again in this case the data from the netgear access ports, will be placed in the native vlan (vlan 2). All other vlans that are placed in the "allowed vlan" statement above, will be tagged as such.

As far as port type general, this gives you a few extra options as outlined in the Dell guide above. After reading the above paragraph, refer back to the multiple options for using the general port type and they should make more sense. IF you wanted to use type general, I think it would look something like this, but would be functionally equivalent in this configuration:
(config)#interface ethernet g1
(config-if)#switchport mode general
(config-if)#switchport general allowed vlan 2, tagged
(config-if)#switchport general pvid 2


Expert Comment

ID: 33519690
Re-reading the above, specifically under the example for port type general, there may be an issue with the "allowed vlan" statement containing vlan 2 and then specifying that it be tagged. This is contradictory to the following line "pvid 2" which states that vlan 2 should be untagged. I am not sure if you would need to leave vlan 2 out of this command line, or if the "pvid 2" command would take precedence over the preceding line requiring vlan 2 to be tagged. I don't have a Dell so I can't test this. But I am sure you can see what I mean and this may take some playing around with if you choose the general port type.  

Author Comment

ID: 33524399
Thanks for the comment.  I will hopefully have a chance to test this and let you know the results.

Author Closing Comment

ID: 33773187
For the moment I have everything setup as Access (general) ports along with the IP Helper and everything is working.

I will later on be adding some more complexity to it which will probably require getting back into the trunking ports a bit more.

Thanks for your assistance.

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