Bridge IDs

Unanswered Question
Sep 9th, 2008

Which of the following Bridge IDs would win the election.

32768:0200.1111.1111

32768:0200.2222.2222

200:0200.1111.1111

0200:0200.2222.2222

40,000:0200.1111.1111

I have this problem too.
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Francois Tallet Tue, 09/09/2008 - 16:02

Assuming there is no trick like 0200 being octal vs 200 decimal;-) I would vote for 200:0200.1111.1111

Regards,

Francois

shane.kearney Wed, 09/10/2008 - 02:00

Am I wrong to think the bridge IDs can only be in multiples of 4096?

by the way you are correct and i was wrong

Giuseppe Larosa Wed, 09/10/2008 - 02:08

Hello Shane,

bridge IDs can only be in multiples of 4096 if using extended system-id otherwise they can be any value between 0 and 65535.

Hope to help

Giuseppe

shane.kearney Wed, 09/10/2008 - 02:19

Last Question,

How do you know if the extended System is used or not?

Thanks for all the help.

Giuseppe Larosa Wed, 09/10/2008 - 05:12

Hello Shane,

two ways

a) from configuration

b) do sh spanning-tree vlan 1

and

sh spanning-tree vlan x

if using extended id:

bridge priority in vlan x will be:

base pri + x

if not using extended id

bridge pri in vlan x = bridge pri in vlan 1

but MAC address differ

(the extended id feature is also called mac address reduction for this reason)

Hope to help

Giuseppe

Francois Tallet Wed, 09/10/2008 - 08:51

Note that even with extended sysid, the priority will end up within the range 0-65535. Sure, you can only configure the higher 4 bits of the priority (by increment of 4096 indeed), but as you eventually add the vlan number to this configured priority, you end up with a figure that utilize the whole 64k range.

Regards,

Francois

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