VLAN Pruning Trick - Revision history

Casey at 18:36, 29 May 2014

2014-05-29T18:36:45Z

Casey at 20:18, 29 July 2013

2013-07-29T20:18:07Z

Casey at 20:13, 29 July 2013

2013-07-29T20:13:48Z

Casey: Created page with "Let's say you have a trunk port, and your sloppy coworkers never bothered to prune the unnecessary VLANs from the "switchport trunk allowed vlan" statement. It's trunking the..."

2013-07-29T20:11:19Z

Created page with "Let's say you have a trunk port, and your sloppy coworkers never bothered to prune the unnecessary VLANs from the "switchport trunk allowed vlan" statement. It's trunking the..."

New page

Let's say you have a trunk port, and your sloppy coworkers never bothered to prune the unnecessary VLANs from the "switchport trunk allowed vlan" statement. It's trunking the entire 1-4094 range, even through they're not all supposed to be there. If there are a lot of VLANs, it will be time consuming to go through and "switch port trunk allowed vlan remove ##" every VLAN or group of VLANs from the list. And a single typo can knock out a bunch of VLANs.

Here's how to make the switch do the work for you.

The list of VLANs that are supposed to be on the port is '''10,20,30,40,50,60,70,80,90,100'''

Find an available port that has no config on it. It doesn't need to be the same switch.

On that port, do this:

<PRE>
switchport trunk allowed vlan remove 10,20,30,40,50,60,70,80,90,100
</PRE>

That will give you a list of the VLANs that aren't supposed to be on the real port:

<PRE style="color:white;background-color:black;font-weight:bold;font-size:1.2em;">
SWITCH#show run int fa0/30
Building configuration...

Current configuration : 227 bytes
!
interface FastEthernet0/30
switchport trunk allowed vlan 1-9,11-19,21-29,31-39,41-49,51-59,61-69,71-79
switchport trunk allowed vlan add 81-89,91-99,101-4094
switchport mode dynamic desirable
shutdown
no cdp enable
end
</PRE>

Copy that list to a text editor, remove the word "add" and put in the word "remove".

<PRE>
switchport trunk allowed vlan remove 1-9,11-19,21-29,31-39,41-49,51-59,61-69,71-79
switchport trunk allowed vlan remove 81-89,91-99,101-4094
</PRE>

Paste that in to your switch, and you'll be left with a nice clean interface.

← Older revision		Revision as of 18:36, 29 May 2014
Line 1:		Line 1:
	Let's say you have a trunk port, and your sloppy coworkers never bothered to prune the unnecessary VLANs from the "switchport trunk allowed vlan" statement. It's trunking the entire 1-4094 range, even through they're not all supposed to be there.		Let's say you have a trunk port, and your sloppy coworkers never bothered to prune the unnecessary VLANs from the "switchport trunk allowed vlan" statement. It's trunking the entire 1-4094 range, even through they're not all supposed to be there.

−	You can't just paste in "switchport trunk allowed vlan 10,20,30", because it may flap the VLANs on the port, and they'll be down until spanning-tree finishes its work. You have to go through and prune out all the individual VLANs using the "~~switch port~~ trunk allowed vlan remove ##" command. If there are a lot of VLANs, it will be time consuming to manually go through and do that for every VLAN or group of VLANs from the list. And a single typo can knock out a bunch of VLANs.	+	You can't just paste in "switchport trunk allowed vlan 10,20,30", because it may flap the VLANs on the port, and they'll be down until spanning-tree finishes its work. You have to go through and prune out all the individual VLANs using the "switchport trunk allowed vlan remove ##" command. If there are a lot of VLANs, it will be time consuming to manually go through and do that for every VLAN or group of VLANs from the list. And a single typo can knock out a bunch of VLANs.

← Older revision		Revision as of 20:18, 29 July 2013
Line 1:		Line 1:
−	Let's say you have a trunk port, and your sloppy coworkers never bothered to prune the unnecessary VLANs from the "switchport trunk allowed vlan" statement. It's trunking the entire 1-4094 range, even through they're not all supposed to be there. If there are a lot of VLANs, it will be time consuming to go through and ~~"switch port trunk allowed vlan remove ##"~~ every VLAN or group of VLANs from the list. And a single typo can knock out a bunch of VLANs.	+	Let's say you have a trunk port, and your sloppy coworkers never bothered to prune the unnecessary VLANs from the "switchport trunk allowed vlan" statement. It's trunking the entire 1-4094 range, even through they're not all supposed to be there.
		+
		+	You can't just paste in "switchport trunk allowed vlan 10,20,30", because it may flap the VLANs on the port, and they'll be down until spanning-tree finishes its work. You have to go through and prune out all the individual VLANs using the "switch port trunk allowed vlan remove ##" command. If there are a lot of VLANs, it will be time consuming to manually go through and do that for every VLAN or group of VLANs from the list. And a single typo can knock out a bunch of VLANs.
		+

	Here's how to make the switch do the work for you.		Here's how to make the switch do the work for you.

@@ Line 2: / Line 2: @@
 Here's how to make the switch do the work for you.
 The list of VLANs that are supposed to be on the port is '''10,20,30,40,50,60,70,80,90,100'''
-On that port, do this:
+Find an available port that has no config on it.  It doesn't need to be the same switch.  On that port, do this:
 <PRE>
@@ Line 29: / Line 29: @@
 end
 </PRE>
 Copy that list to a text editor, remove the word "add" and put in the word "remove".
@@ Line 36: / Line 37: @@
   switchport trunk allowed vlan remove 81-89,91-99,101-4094
 </PRE>
 Paste that in to your switch, and you'll be left with a nice clean interface.