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VLAN NUMBER QUERY

Posted on 2011-02-27
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Last Modified: 2012-05-11
Im aware of the following:

Default vlan ranges:

1 - Cisco
2 - 1001 - Ethernet used for 'Server/Client'
1002 - 1005 - FDDI
1025 - 4094 - Ethernet also but used with 'Transparent mode'

Ive worked for Datacentres and only seen vlan number ranges in the Single or double figures, but either way presumably as per my info above, a vlan can use a high vlan number as high as 1001?

As ive never worked for small companies do they configure their vlans in the ranges of 1025-4096 setup as 'Transparent', as I have only known lower numbers to ever be used?


can someone advise!!
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Question by:mikey250
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Kvistofta earned 168 total points
ID: 34992009
To keep compatibility between all brands of device I suggest you to keep your vlans in the range below 1001.

/Kvistofta
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Author Comment

by:mikey250
ID: 34992057
the only highest vlan number ive seen has only been in double figures ie vlan 20 for eg.  so dependant on how old some peoples/companies equipment is being below 1001 and below is a safer range to stay below.  ok

yes but for server/client this is ok!!

what about 'transparent'?

I have set 20 30 or whatever on a 'transparent' before but wanted to know if the default ranges are those I mentioned why can or should i use lower?

useless information i realise, just would like to know!!
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by:Kvistofta
Kvistofta earned 168 total points
ID: 34992325
There is never ever any problems using id:s up to 1000. The 802.1q-standard is valid for id:s up t0 4094 but different vendors might or might not support vlan id:s above 1004, for example older cersions of Cisco IOS.

I guess that you with "transparent" means the VTP-mode, right? Transparent just means that the switch doesnt take part of vtp and any vlan id supported by that device can be used.

20, 100 or 900 doesnt matter. If you stay below 1000 you will never have any issues.

/Kvistofta
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by:Don Johnston
Don Johnston earned 332 total points
ID: 34993934
The only time you'll run into problems with VLAN IDs over 1000 is if you need to run ISL trunks (which only have a VLAN ID field of 10-bits). If all of your trunks are 802.1q, then there won't be any problems with VLAN ID's up to 4094.

The reason why you probably haven't seen larger VLAN numbers is they weren't needed in the networks you were working with (they didn't need more than 1000 VLANs).
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Author Comment

by:mikey250
ID: 34997463
according to my book, 'Transparent mode' for VTP yes, has cisco default vlans starting from 1025-4094 not 20, 100 or 900 for example although yes Ive used lower than the default, so im wondering what is going on?

it does not mention in my book anything about 10 bit for ISL, as all it shows is:

DA - Destn address
SA - Source address
Ethertype/Length - ty-e
Data - info inside
FCS - Error checking

Where as 802.1Q - shows 12 bits
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by:Don Johnston
Don Johnston earned 332 total points
ID: 34999370
VTP was designed with ISL in mind. Which is why VTP only supports the propagation of VLANs 1-1023. So I guess that I should have said "if all of your trunks are 802.1q AND you're not running VTP, then there won't be any problems with VLAN ID's up to 4094"

There's a whole bunch of stuff in that 26 ISL header. :-) The 10-bit VLAN ID field is just one of the fields.
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Author Comment

by:mikey250
ID: 35010007
oK "if all of your trunks are 802.1q AND you're not running VTP, then there wont be any problems with VLAN ID's upto 4094."

Ok but if im using 'MST' which allows vlans to cross trunks for example labelled as one 'Region' then does this mean VTP cannot be used?

im assuming then that only with 'ISL' I can cross trunks with 'MST' then?
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by:Don Johnston
Don Johnston earned 332 total points
ID: 35010413
VTP and STP aren't related. You can use VTP with any STP you want.

MST in an industry standard (802.1s). It works fine with 802.1q trunks.
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Author Comment

by:mikey250
ID: 35010550
I haven't mentioned STP.
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Author Comment

by:mikey250
ID: 35010574
trying to understand:

oK "if all of your trunks are 802.1q AND you're not running VTP, then there wont be any problems with VLAN ID's upto 4094."?

Ok but if im using 'MST' which allows vlans to cross trunks for example labelled as one 'Region' then does this mean VTP cannot be used?

im assuming then that only with 'ISL' I can cross trunks with 'MST' then?
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by:Don Johnston
Don Johnston earned 332 total points
ID: 35014011
>does this mean VTP cannot be used?

No. All VTP does is propagate the VLAN database. It doesn't have anything to do with spanning-tree.

You can use RPVST+ or MST with 802.1q or ISL.

You can use VTP with 802.1q or ISL.

You can use VTP with RPVST or MST.

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Author Comment

by:mikey250
ID: 35016255
ok no problem!  thanks for useful points of clarification
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