VLANs across WAN

mark.wood · ‎12-12-2007

We have several sites linked by 10MB leased lines. They are generally connected by 3560 switches and are members of the same VTP domain. I have two questions:

1. VLAN information is propogated correctly and the spanning-tree root is selected according to the switch config for every VLAN except VLAN1, which is always located at the switches local site. Why does this happen and is it important?

2. We are considering putting a group of our servers in a single VLAN that spans all of the sites (servers only, no PCs). Is this a bad idea?

Many thanks

Mark

richf · ‎12-12-2007

I personally do not like spanning VLANs across slow links. The reason being an issue at one site can down your entire network by flooding all the links. I have seen this on campuses with gig links. If you have the ability to do it connect your sites with L3 links and use a routing protocol like EIGRP. Otherwise use transparent VTP, and configure each VLAN per switch and do not let them traverse your uplinks.

As for #1 this is normal for VLANS which have not been specifically set for root.

Here is a link on how to do that.

http://www.cisco.com/en/US/docs/switches/lan/catalyst3560/software/release/12.1_19_ea1/configuration/guide/swstp.html#wp1039614

skhirbash · ‎12-12-2007

This topic touched on a question that I was intending to post. I have a lab consisting of 3 segments;

Segment 1: R1 with 2 swithces: 5 VLANS, ports trunked with dot1q, vtp was configured, sub-interfaces have been configured with different subnets for each VLAN, and everything is working just fine.

Segment 2 and 3: uplink ports and interswitching ports have been trunked with dot1q, vtp domain has been set; however, the VLANs from segment 1 aren't traversing to segment 2 or 3. What am I missing here?

Thanks,

sK

padramas · ‎12-12-2007

Hello All,

I had posted similar question few months ago.

Here is the link

http://forum.cisco.com/eforum/servlet/NetProf?page=netprof&forum=Network%20Infrastructure&topic=LAN%2C%20Switching%20and%20Routing&CommCmd=MB%3Fcmd%3Ddisplay_location%26location%3D.1ddfdf9f

Experts might be able to help us further on this issue.