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?
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