Posts Tagged ‘VLAN’

Quite often I hear people reference the Native VLAN and they’re unsure what exactly they’re talking about. In the RFC standards “Native” is considered an “Untagged” VLAN on a port and that is the preferred terminology. So, this is really simple, “native” means “Untagged” because on each Cisco “Trunk” port you can have a different native VLANs on each Cisco “Trunk” port. Thus, the concept of a native VLAN isn’t always VLAN 1 it is just a convenience that VLAN 1 is the default VLAN on Cisco switches when they’re unpacked and that confuses most people. In reality, you won’t have an untagged port on a Cisco trunk because you’d rather have all inter-switch traffic tagged to prevent VLAN-hopping.


You can’t disable spanning-tree on a per-port bases in IOS but you can disable spanning tree per VLAN using the global command:

no spanning-tree vlan vlan-id


If you’re using the HP A-series E5500 switches and find that filtering traffic between VLANS whose layer 3 interfaces reside on that switch are not working, I have found the solution if you’re using the 2215 code.

Quite simple, downgrade to the 2208 or 2210 code because as of this writing 08/21/2012 they are working on the bugs in the 2215 code


Core vs. Edge Routing Topology

There isn’t a lot of talk about this; however, there is a lot of training material that references this debate and makes recommendations for edge based routing. For those not familiar with the topic I am talking about “Campus LANs” and not ISP networks where you essentially have to push routing to the edge for some customers. In my article I am talking about Core vs Edge in the aspect of where we perform all of our routing in a “Campus LAN” Read the rest of this entry »


Let me start by saying that Superscopes are not a standard mechanism of DHCP, just a “hack” by Microsoft to support networks that don’t understand the concept of “1 IP subnet PER vlan, not 10 IP subnets per VLAN”. The only, and I do mean ONLY, time that you use Superscopes is when you have a network design that has multiple IP subnets inside the same VLAN. Let me explain the ONLY instance where this is needed and WHY you need multiple interfaces configured for this to work… Read the rest of this entry »