Summary Advertisement in VTP

Answered Question
Jan 4th, 2014
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1. What is the code for an "Summary Advertisement" whereas it is 0x03 for 'Advertisement Request'

2. Can someome please expain about the followers field in a 'Summary Advertisement' ? What does it holds?

I understood that inthis way:It tells the receiving switch that after this message you're going to receive summary advertisements. I'm i correct? If yes what value does it put's in that field.

3. If the switches exchanged the 'Summary Advertisement' if they found that the configuration revision value is same, even then will they sendout subset advertisement?


Regards,

Chandu                        

Correct Answer by Rolf Fischer about 3 years 7 months ago

Hi Chandu,


the VTP message codes are:


0x01: Summary Advertisement

0x02: Subset Advertisement

0x03: Advertisement Request

0x04: Join (=> Pruning)

0x05: ? (VTPv3, I've captured such PDUs but couldn't find out what they are so far)


The Summary Advertisements are send in 5-minute intervals just to make sure that VLAN information keeps synchronized within the domain (e.g. for new devices). The followers field is set to zero in this case.

If a change is made in the VLAN configuration and the Configuration Revision increases, a Summary Advertisement is send with the followers fields set to one, which means that a Subset Advertisement will follow (containing the detail information), so that new information can will be populated within the domain immediately after the change.

You can see this sequence in the Wireshark capture file I've attached.

I don't know if PT supports debug commands, a "debug sw-vlan vtp events" provides some interesting output as well:


VTP LOG RUNTIME: Summary packet received, domain =VTPTEST , rev = 8, followers = 0, length 77, trunk Gi0/1

VTP LOG RUNTIME: Summary packet rev 8 equal to domain VTPTEST rev 8

VTP LOG RUNTIME: Summary packet rev 9 greater than domain VTPTEST rev 8

(...)


HTH

Rolf

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Correct Answer
Rolf Fischer Sat, 01/04/2014 - 03:26
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Hi Chandu,


the VTP message codes are:


0x01: Summary Advertisement

0x02: Subset Advertisement

0x03: Advertisement Request

0x04: Join (=> Pruning)

0x05: ? (VTPv3, I've captured such PDUs but couldn't find out what they are so far)


The Summary Advertisements are send in 5-minute intervals just to make sure that VLAN information keeps synchronized within the domain (e.g. for new devices). The followers field is set to zero in this case.

If a change is made in the VLAN configuration and the Configuration Revision increases, a Summary Advertisement is send with the followers fields set to one, which means that a Subset Advertisement will follow (containing the detail information), so that new information can will be populated within the domain immediately after the change.

You can see this sequence in the Wireshark capture file I've attached.

I don't know if PT supports debug commands, a "debug sw-vlan vtp events" provides some interesting output as well:


VTP LOG RUNTIME: Summary packet received, domain =VTPTEST , rev = 8, followers = 0, length 77, trunk Gi0/1

VTP LOG RUNTIME: Summary packet rev 8 equal to domain VTPTEST rev 8

VTP LOG RUNTIME: Summary packet rev 9 greater than domain VTPTEST rev 8

(...)


HTH

Rolf

chandra_rc16 Mon, 01/06/2014 - 22:43
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Thanks a lot Rolf.


And PT is supporting debug for vtp events, it was very helpful.

So the follower field is just to indicate if there are any subset advertiesements that are going to be transmitted or not. If yes then the count of the subset advertisement messages will be placed in the followers field.


Thanks again for the wireshark captures.


Regards,

Chandu

Rolf Fischer Tue, 01/07/2014 - 05:25
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Chandu, you're welcome. Thanks for the feedback.


So the follower field is just to indicate if there are any subset  advertiesements that are going to be transmitted or not. If yes then the  count of the subset advertisement messages will be placed in the  followers field.



That's actually a more precise description than what I wrote.

You're correct: When the vlan information cannot be storred in a single frame, more than one Subset Advertisement has to be sent and the number is indicated in the followers field:


VTP LOG RUNTIME: Summary packet received, domain = VTPTEST, rev = 1, followers = 2, length 77, trunk Fa0/0

VTP LOG RUNTIME: Summary packet rev 1 greater than domain VTPTEST rev 0

VTP LOG RUNTIME: Subset packet received, domain = VTPTEST, rev = 1, seq = 1, length = 1468

VTP LOG RUNTIME: Subset packet received, domain = VTPTEST, rev = 1, seq = 2, length = 1324


Cheers,

Rolf

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