[c-nsp] 3750 Metro internal vlan allocation for loopback?

[Jared Gillis]

Hi Manu,

I did try what you suggested. Simply shutting the lo1 interface wasn't enough to remove the internal vlan assignment, the only way I could make that happen was to delete the lo1 interface and reload the chassis (ouch). Post-reload, I manually assigned vlan 1006 and gave it a name as you suggested, and then re-created lo1. This time it took vlan 1007.

This isn't really a solution for me, because my deployed switches have many vlans assigned to them, in ascending order, so 1007 is usually in use (this continues up to 1050 or so on some switches).

If I could change the vlan allocation policy, I could work around this issue by letting lo1 take vlan 4000 or so. This isn't possible on 3750s though:
vlan internal allocation policy ?
  ascending  Allocate internal VLAN in ascending order

No descending option. =(

On 10/25/2011 02:05 PM,  wrote:
> Hi Jared,
> 
> Have you tried this:
> 
> conf t
> int lo1
> shut
> exit
> vlan 1006
> name HANDS_OFF
> exit
> int lo1
> no shut
> 
> Shutting down the loopback will let you reconfigure vlan 1006 and when
> you re-enable the loopback, it'll assign the next available internal
> vlan to it (you can't manually assign an internal vlan). Not sure why it
> ignored your existing vlan 1006 on code upgrade though. Bug?...
> 
> 
> Manu.
> (Feel free to feed this back into the list but please remove any mention
> of my email address - thanks)
> 
> 
> 
>> -----Original Message-----
>> From: cisco-nsp-bounces at puck.nether.net [mailto:cisco-nsp-
>> bounces at puck.nether.net] On Behalf Of Jared Gillis
>> Sent: 25 October 2011 20:39
>> To: cisco-nsp at puck.nether.net
>> Subject: [c-nsp] 3750 Metro internal vlan allocation for loopback?
>>
>> Hello,
>>
>> I just upgraded one of my 3750ME switches from 12.2(46)
> (c3750me-i5k91-
>> mz.122-46.SE.bin) to 12.2(58) (c3750me-i5k91-mz.122-58.SE2.bin) and
>> suddenly the switch has allocated an internal vlan for the loopback
>> address:
>>
>> #show vlan internal usage
>>
>> VLAN Usage
>> ---- --------------------
>> 1006 Loopback1
>>
>> interface Loopback1
>>  description Primary Management/Peering IP
>>  ip address a.b.c.d 255.255.255.255
>>
>> This internal vlan usage did not occur on the older code, and is a
>> problem because I've got 80+ of these out in the field, and I've
>> manually used 1006 on almost all of them. When the router reloaded
> from
>> the code upgrade, it blew away my manually configured vlan 1006.
>>
>> I need to find some way to work around this new "feature". The 3750
>> won't let me change the vlan allocation model to start high and count
>> down, and I can't find any way to manually assign a vlan to the
>> loopback address.
>>
>> Additionally, I am curious why this behavior changed suddenly. I can
>> find no mention of this in Google or on Cisco's site.
>>
>> Does anyone have any suggestions for this?
>>
>> Thanks,
>> Jared Gillis
>> _______________________________________________
>> cisco-nsp mailing list  cisco-nsp at puck.nether.net
>> https://puck.nether.net/mailman/listinfo/cisco-nsp
>> archive at http://puck.nether.net/pipermail/cisco-nsp/
>>
>>
>>
>>
>> ***************************************************************
>> The information contained in this e-mail and any files transmitted 
>> with it is confidential and may be subject to legal professional 
>> privilege. It is intended solely for the use of the addressee(s). 
>> If you are not the intended recipient of this e-mail, please note 
>> that any review, dissemination, disclosure, alteration, printing, 
>> copying or transmission of this e-mail and/or any file transmitted 
>> with it, is prohibited and may be unlawful. 
>> If you have received this e-mail by mistake, please promptly 
>> inform the sender by reply e-mail and delete the material. 
>> Whilst this e-mail message has been swept for the presence of 
>> computer viruses, eircom does not, except as required by law, 
>> represent, warrant and/or guarantee that the integrity 
>> of this communication has been maintained nor that 
>> the communication is free of errors, viruses, interception or 
>> interference. 
>>
>> eircom Limited. Private Company Limited by Shares. 
>> Registered in Dublin. Registration Number 98789.
>> Registered Office - 1 Heuston South Quarter, St. John’s Road, Dublin 8.
>>
>> ***************************************************************