Vlan & Hubs

Everything will be tagged VLAN2.

Regards, Steve

In article , wrote: :I have a vlan with 3500 series switches.

:If I have the switchport a hub is plugged into configured on vlan2, :will everything on the hub also be in vlan2 or will it be untagged?

It depends on whether the port is configured as an "access" port or a trunk, and if it is a trunk, it depends on what the "native" vlan setting is for the port. Ona trunk, everything except the "native" vlan (sometimes called the Primary Vlan ID) will be tagged.

Note: if you are running a tagged vlan onto a hub, it is possible that you will have problems. The VLAN tag extends the maximum ethernet packet size by a few bytes, so if the hub has more intelligence than merely blindly regenerating and redistributing signals, the hub could end up rejecting the longer packets.

Hi Walter,

I think the frame is restored to normal by the time it exits the switch port, unless the port is a trunk connection. Otherwise, a NIC plugged in to the port would have similar problems with the frame.

Bill

|> :If I have the switchport a hub is plugged into configured on vlan2, |> :will everything on the hub also be in vlan2 or will it be untagged?

|> It depends on whether the port is configured as an "access" port or |> a trunk, and if it is a trunk, it depends on what the "native" vlan |> setting is for the port.

|I think the frame is restored to normal by the time it exits the switch |port, unless the port is a trunk connection.

As I said, it depends on whether the port is configured access or trunk. And in the case of a trunk connection, it -also- depends on the native VLAN setting.

|Otherwise, a NIC plugged in |to the port would have similar problems with the frame.

The OP does not currently -have- a hub connected and wants to know whether it is safe to do so. The OP did not indicate whether the port is access or trunk, and if trunk whether the vlan was the native one or not, and the OP did not indicate what is to be connected through the hub. So the best we can say is "Maybe".

The OP might, for example, be wanting to use a hub in order to be able to sniff the traffic without using SPAN/RSPAN. Will the vlan information be there or not? It doesn't depend on the fact that it is a "hub" connected up, it depends on how the port is configured.

The one thing implied by hooking up a hub is that you will certainly be forced to half duplex.

To be more specific, here is my actual scenario.

Currently, we have a mobile tractor trailer with about three pc's in it that links up to a cat 5e connection outside our building - a hospital. .

The Rig is not ours; it's a third party vendor - a PET scanner to be exact.. Inside the rig they have three pc's hooked up to a netgear hub. Also on the netgear hub they have a small router. On their router they have one of our IP addresses assigned as their secondary ip. That is how they route on our network.

Recently we installed a PACS system (medical imaging) on our network

- which is bandwidth intensive.. We have several legacy novell (ipx) servers generating butt loads of broadcasts. Our entire network moves at a snails pace. I only took over the network recently and need to get things efficient. I have 700 nodes on a flat network being routed by a 2691.

What I want to do is to create a vlan for the pacs servers, etc, and I would like the outside rig's hub to be tagged in that vlan. Is that possible with their existing equipment?

TIA!

In article , wrote: :To be more specific, here is my actual scenario.

:Inside the rig they have three pc's hooked up to a :netgear hub.

:What I want to do is to create a vlan for the pacs servers, etc, and I :would like the outside rig's hub to be tagged in that vlan. Is that :possible with their existing equipment?

Dunno, you didn't say which model of Netgear hub.

DG834G DM602 DS104 DS106 DS108 DS116 DS309 DS508 DS516 DS524 EA101C EA201C EN104 EN104TP EN106TP EN108 EN108TP EN116 EN308 EN308TC EN516 EN524 FA101 FA120 FA310TX FA311 FA331

The EN10x* series have automatic partitioning to protect against "jabber", which you would not have on a simple multi- port repeater, as a plain repeater would not know or care where a frame started or ended. Therefore at least some of the Netgear hubs have ideas about what a valid packet length is, so there is the possibility that some of the won't like the extra packet length due to vlan tags.

There is a relatively simple work-around to this: you could slightly lower the MTU on the link. That might end up creating a lot of fragments, though, which is not good for performance.

:The Rig is not ours; it's a third party vendor - a PET scanner to :be exact.. Inside the rig they have three pc's hooked up to a :netgear hub.

My advice would be to get rid of the hub and replace it with a switch that supports 802.1Q. But is the hub even really involved? You mentioned they have a router at that end. You aren't going to get the PC's at that end to support VLAN tags themselves, so something is going to have to strip off the VLAN tags: that would be the router, and that router should be strictly between you and the hub.

If the 3rd party won't agree to install a switch, then they aren't going to agree to you wanting to reconfigure the router to support

A possibly easier approach would be to put in a simple switch between your router and your link to them. The switch will act as a traffic filter, leaving all the cross-hub traffic off your net. You'll still get hit with all of their NETBIOS broadcasts...

Is there a reason why their router must be directly in your main VLAN and address space? Perhaps a simple Linksys BEFS* or BEFW* nat'ing router between you and them would do a lot. Does your new PACS rely on broadcasts, or would your PACS not work properly if you were PAT (Port Address Translating) those PCs down into a single IP ?