vtp summary advertisements, subset advertisements.

Answered Question
Jan 10th, 2009

Hi every body!

I have few questions:

1)Does each subset advertisement carry single vlan information?

2)My book says about" Advertisement request from clients"

(Here the client refer to switch in vtp client mode)

" A vtp client can request any vlan information it lacks"

The question is how does switch determine it lacks particular vlan information?

You might say when switch in client mode receives summary advertisement with high config number, client switch can know if it lacks particular vlan information.

My point is high config number shows the updated information, and there is no field in summary advertisement for vlan information.

The feild in summary advertisements are:

version/type/number of subset advert to follow/domain name length/management domain name/config revision number/updater identity/update time stamp/md5 digest hash code.

There is no field for vlan information.

Any thoughts about it?

thanks a lot!

I have this problem too.
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Correct Answer by lejoe.thomas about 7 years 11 months ago

Hi Sarah,

Yes it is.

Lejoe

Correct Answer by lejoe.thomas about 7 years 11 months ago

Hi Sarah,

1) No the subset information can carry information for many vlans

2)Advertisement request is send when a switch changes its VTP domain or it receives a summary advertisement with higher config revision number. In the summary advertisement, there is field which indicates the number of subset advertisements (contains vlan information) that will be included next. So lets say the client expected to receive 4 subset adv based on the summary advertisement. It got only the 3, it can request the subset instance 4.

So by keeping track of subset advertisement it should receive based on summary advertisement, the switch knows whether or not it lacks VLAN information.

HTH

Lejoe

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Correct Answer
lejoe.thomas Sat, 01/10/2009 - 18:53

Hi Sarah,

1) No the subset information can carry information for many vlans

2)Advertisement request is send when a switch changes its VTP domain or it receives a summary advertisement with higher config revision number. In the summary advertisement, there is field which indicates the number of subset advertisements (contains vlan information) that will be included next. So lets say the client expected to receive 4 subset adv based on the summary advertisement. It got only the 3, it can request the subset instance 4.

So by keeping track of subset advertisement it should receive based on summary advertisement, the switch knows whether or not it lacks VLAN information.

HTH

Lejoe

sarahr202 Sat, 01/10/2009 - 19:22

Thanks Lejoe!

Here is my understanding from my book.

1)vtp server switch sends summary advertisements with higher confg number 6, at this time the field ' number of subset advto follow" is empty.

2)vtp client switch finds the config revision number higher and check the domain name if it matches. At this time client switch does not know if it needs any information for a particular vlan. All it knows the vtp server has updated information.

3) client send request to vtp server.

4)vtp server sends summary advertisements this time with the number of subset advertisement to follow.

5)client switch receives the summary advertisement and then wait for subset advertisements indicated in summary advertisements.

Is it correct understanding?

thanks a lot!

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