[rancid] VLAN information flapping since 3.0

[David Adam]

Over the years, I see many threads[1][2][3] discussing the 
oscillating/flapping of output as VLAN members change in response to links 
going up and down. The consensus seems to be that this is not desirable 
behaviour.

Interestingly, we've just upgraded from 2.3.8 to 3.6.2 and this behaviour 
has appeared. It looks like the test was changed in 3.0[4] to switch from 
showing VLANs except in transparent/server VTP mode to showing VLANs 
except in VTP client mode.

We have VTP disabled entirely (VTP Operating Mode: Off) on our Cisco 4507, 
but are having problems with frequent updates to the configuration 
appearing in our system with machines being powered up and down[5].

In ios.pm, is there any sense in setting "DO_SHOW_VLAN" to 1 in cases 
where VTP is disabled entirely? All the VLAN configuration is contained in 
`show running-config`, so it's not like we're losing anything here. I've 
patched my local version for now.

Alternatively, could it be stripped if FILTER_OSC is turned on?

My perl is very ordinary, but it seems like the variable is misnamed: I 
think it should be called DONT_SHOW_VLAN. 

Thanks

David Adam
zanchey at ucc.gu.uwa.edu.au

[1]: 
http://www.shrubbery.net/pipermail/rancid-discuss/2010-July/005054.html
[2]: 
http://www.shrubbery.net/pipermail/rancid-discuss/2011-February/005487.html
[3]: 
http://www.shrubbery.net/pipermail/rancid-discuss/2017-January/009387.html
[4]: 
http://www.shrubbery.net/pipermail/rancid-discuss/2013-August/007001.html
[5]: 
http://cvs.ucc.asn.au/cgi-bin/viewvc.cgi/rancid/ucc/configs/bitumen.ucc.gu.uwa.edu.au?r1=398&r2=399