Rebuild VLAN to VTP

[David Kondicz]

Hi,

we have a big MAN network based on licensed radios. On each hop is of course Cisco SW 2960 witl LAN BASE or ME 3400.

I want rebuild out static VLAN configs on switches. At this time we are using only 1 Trunk line fo 2 Vlans.

The problem is that on 1 side of radio link we have VLAN1 and the other side of radio link we have VLAN2 (Vlans are changing on each radio hop but it is the same network). In this situation i think we cant makeTRUNKING for other vlans on this radio link.

Solution?

Will it helps if I configure one VLAN for eg VLAN 50 that will be used for our MAN netwok on each switch? After that on uplinks and downlink i configure switchport mode trunk,  switchport trunk allowed vlan 50-300 on all switches in our network?

After that configure VTP

server will be in the centre of star topology. All other switch are on clients mode.

And is possible to change VLANs from VLAN 1 o VLAN 2 to VLAN 50 withot blackout ?

Thank you

Best regards

Dave

[ajasti]

Dave,

For your first question where one side of radio link is on vlan 1 and other side is on vlan 2, you were correct in saying that 'trunking' will not work. This is classic example of vlan leaking where data from one vlan goes into other vlan. Works fine on access ports. But on trunk ports, usually you will see 'native vlan mismatch' errors or tagging issues; once trunk encapsulation is in place, packets from a certain vlan are placed back into same vlan on other end of trunk.

For second question, I don't think it's possible because, once you add a switch to a VTP domain as client, its vlan database is refreshed with the server copy. So, all the vlans configured manually on a switch will be wiped out.

VTP is just for vlan database management and has no control over how trunks are configured and what vlans are being passed. So typical configuration flow is i. configure trunk ports, ii. configure VTP server, iii. configure VTP clients.  If you have multiple switches with VTP already configured, change them to transparent, make VTP changes and then revert them back to clients. This process will make sure VLAN database on VTP server remains intact.

Changing Vlans is possible but not on a trunk port and it's definitely not a scalable solution. Would prefer to fix the vlan configuration on radio links and you can implement trunking w/o any issues.

Regards,

AJ

[David Kondicz]

Hi AJ

exastly as you worte! Log message of native VLAN mismatch is on all of our switches.

As you wrote i think only solutin will be manualy set one VLAN for network on radio link, for eg. VALN 50 in whole network and manualy configure trunk allowed vlan 50-300.

Am I right?

Thank you!

BR Dave

[ajasti]

Correct. Once you decide on a Vlan for radio link (vlan 50), you can configure trunks. If you think most of the traffic will be on Vlan 50, assign it has native vlan; reduces tagging overhead on switches.

Sample config for the ports connected to radio links:

interface

switchport trunk encapsulation dot1q

switchport trunk native vlan 50 <<<< Optional

switchport trunl allowed vlan 50 - 300

Switcport mode trunk

As long as your radio links are point-to-point (no mesh network), you shouldn't see any issues.

AJ.

[David Kondicz]

Thank you!

But must i use native vlan ? Can I use simple vlan? Our radios are supporting vlan packets.

Thank you

BR

dave

[ajasti]

Dave,

By default, native vlan is 1. Not sure what you meant by 'simple vlan', but you can use any vlan as native vlan as long as it is configured same on both sides of the link.

Traffic in native vlan goes untagged. Typically it is either the managment vlan or the vlan with most traffic is set as Native vlan.

AJ

[David Kondicz]

Sorry,

as simple vlan i mean - switchport acces vlan 50

i just dont know what is the different betwen - switchport acces vlan 50 and switchport acces native vlan

I just never used native vlan in config before

[ajasti]

Thanks for the clarification.

Switchport access vlan 50   --  This command is used when a port is configured as access.Port will allow ONLY vlan 50 traffic only. No other vlan traffic will be allowed.

switchport trunk native vlan 50 - This command is used when a port is configured as trunk.Port will all VLANS which are being allowed on trunk port (Default 1-4094 vlans). If you want to allow vlans 50 to 300, then you have configure the port as trunk.

Native Vlan: When you configure a trunk, all frames in all vlans except native vlan gets tagged so that destination knows to which vlan receiving frame belongs to. Native vlan (by default vlan 1) doesn't get tagged (Frames remains untouched). An untagged traffic goes into native vlan at the destination.

AJ.