cancel
Showing results forĀ 
Search instead forĀ 
Did you mean:Ā 
cancel
320
Views
3
Helpful
4
Replies

VLAN configurations on trunk ports

Manish Manwal
Level 1
Level 1

Hi 

I have a question regarding VLAN configurations on trunk ports for Cisco switches. Specifically, if I remove some VLANs from the trunk port configuration, is there any impact on the traffic for the remaining VLANs on that port?

For example, if a trunk port currently allows VLANs 10, 20, and 30-40, 60 62 and I decide to remove VLAN 30-40, 60 62 from the allowed VLANs list, will this affect the traffic for VLANs 10 and 20 on that trunk?

and how to remove the vlans is below command is correct?( nexus Switches)

switchport trunk allowed vlan remove 30-40, 60, 62

Thanks for your help!

THANKS
MANISH MANWAL
4 Replies 4

switchport trunk allowed vlan remove 30-40, 60, 62 <<- this command correct 

If your SW is  not transport between two SW then you can remove it' if not keep it.

If you dont get this point please ask anything not clear

MHM

current config is 

interface Ethernet1/38
switchport
switchport mode trunk
no shutdown

 

and client wants to allow only VLAn 100, 86 and 90. is there any impact of adding just these vlan if i run below command?

switchport trunk allowed vlan add 100,86,90

THANKS
MANISH MANWAL

Yes that's correct. Make sure you are NOT using one of those removed VLANs to access that device or others. You will lose connectivity immediately.

 

-David 

Joseph W. Doherty
Hall of Fame
Hall of Fame

@Manish Manwal wrote:

I have a question regarding VLAN configurations on trunk ports for Cisco switches. Specifically, if I remove some VLANs from the trunk port configuration, is there any impact on the traffic for the remaining VLANs on that port?

For example, if a trunk port currently allows VLANs 10, 20, and 30-40, 60 62 and I decide to remove VLAN 30-40, 60 62 from the allowed VLANs list, will this affect the traffic for VLANs 10 and 20 on that trunk?


Most any configuration change, even successful, has the potential to affect the traffic subject to the change.  However, for this specific change, if there is an impact, it's likely to be just a network "blip".  I.e. possibly a few packets will be dropped or delayed; usually not very noticeable.

To avoid any possible impact, configuration changes should be restricted to a scheduled maintenance period where all network users are aware of a possible impact.

Interestingly, the last company I worked at had, set aside the time period, 12 AM to 6 AM (local to network being changed), available every day, for performing any maintenance.  We only needed to submit a "change" request, which included a description of the work to be done.  Even a change as simple as yours, would follow this process, and for a change like yours, the "paperwork" to allow the change would take much longer than the change itself.  But, this "paperwork" kept track of who was doing what (and did what) and also precluded different engineers bumping heads.  It was also reviewed/approved by a senior or principle engineer, NetOps and management.  (A very "vetted" approach, but with 5,000 Enterprise network devices and 100,000 users, taking down a huge chunk of the Enterprise network was not well received, especially during business hours.)

Even if you're just a one network engineer shop, you might want to consider what of the above you might mimic, such as keeping your manager, and network users, apprised (or their agreement to) when changes will be make, and actually knowing exactly what you're going to do when you make your changes.  There is some benefit to CYA - laugh.

Review Cisco Networking for a $25 gift card