09-02-2017 03:14 AM - edited 03-08-2019 11:54 AM
Hey fellow geeks, you were so helpful with my other VTP question I found another here.
I was working within a lab environment on Switch A and Switch B connected by a single trunk port, and configured VLAN 12, both in Server mode running version 2 VTP. I entered only the domain name "CCNP" on Switch A, and Switch B dynamically learned it and its VLAN, and changed its domain name to CCNP as well.
So I then manually configured the switch with a domain name of "ccnp" to see what the reaction would be on Switch B, and configured in the output of "sh vtp status" the Domain name changed, but it still has the VLAN 12 lingering on it.
I have tried doing first a wr, reload, then delete vlan.dat / reload, yet the VLAN remains.
Does anyone know what causes this behavior, that even though there are only two switches, both running version 2 but using different Domain Names, why Switch B is having Switch A's VLAN stuck in its config?
Any input appreciated, thanks!
Solved! Go to Solution.
09-02-2017 03:41 AM
Hi David,
I was working within a lab environment on Switch A and Switch B connected by a single trunk port, and configured VLAN 12, both in Server mode running version 2 VTP. I entered only the domain name "CCNP" on Switch A, and Switch B dynamically learned it and its VLAN, and changed its domain name to CCNP as well.
This is expected. A switch whose domain name is empty (sometimes shown as NULL) will adopt the first non-null domain name it hears from its neighbor. Once you configured Switch A with a domain name, it sent out a series of VTP messages indicating its new name, and Switch B - considering itself unconfigured yet - adopted the non-null domain name happily along with the VLAN database from Switch A.
So I then manually configured the switch with a domain name of "ccnp" to see what the reaction would be on Switch B, and configured in the output of "sh vtp status" the Domain name changed, but it still has the VLAN 12 lingering on it.
This is also expected. You have changed the domain name, but you did not touch the VLAN database contents, so whatever the switch B had learned before the domain name change, it retained it afterwards. Changing a domain name is not going to erase the existing VLANs on a switch, it is just going to make the switch stop sharing and synchronizing its VLAN database with the neighbors whose domain name is different.
I have tried doing first a wr, reload, then delete vlan.dat / reload, yet the VLAN remains.
There are multiple possible reasons why the VLAN 12 was recreated:
You would actually need to do write erase, delete vlan.dat, and reload with Switch B disconnected from Switch A to make sure that it does not sync up to it again.
Feel welcome to ask further!
Best regards,
Peter
09-02-2017 03:41 AM
Hi David,
I was working within a lab environment on Switch A and Switch B connected by a single trunk port, and configured VLAN 12, both in Server mode running version 2 VTP. I entered only the domain name "CCNP" on Switch A, and Switch B dynamically learned it and its VLAN, and changed its domain name to CCNP as well.
This is expected. A switch whose domain name is empty (sometimes shown as NULL) will adopt the first non-null domain name it hears from its neighbor. Once you configured Switch A with a domain name, it sent out a series of VTP messages indicating its new name, and Switch B - considering itself unconfigured yet - adopted the non-null domain name happily along with the VLAN database from Switch A.
So I then manually configured the switch with a domain name of "ccnp" to see what the reaction would be on Switch B, and configured in the output of "sh vtp status" the Domain name changed, but it still has the VLAN 12 lingering on it.
This is also expected. You have changed the domain name, but you did not touch the VLAN database contents, so whatever the switch B had learned before the domain name change, it retained it afterwards. Changing a domain name is not going to erase the existing VLANs on a switch, it is just going to make the switch stop sharing and synchronizing its VLAN database with the neighbors whose domain name is different.
I have tried doing first a wr, reload, then delete vlan.dat / reload, yet the VLAN remains.
There are multiple possible reasons why the VLAN 12 was recreated:
You would actually need to do write erase, delete vlan.dat, and reload with Switch B disconnected from Switch A to make sure that it does not sync up to it again.
Feel welcome to ask further!
Best regards,
Peter
09-04-2017 04:17 PM
Wow that was conclusive, thank you so much for that input!
09-05-2017 01:02 AM
David,
You are very much welcome!
Best regards,
Peter
Discover and save your favorite ideas. Come back to expert answers, step-by-step guides, recent topics, and more.
New here? Get started with these tips. How to use Community New member guide