From: Carlos G Mendioroz (tron@huapi.ba.ar)
Date: Thu Aug 12 2004 - 14:45:44 GMT-3
I've just labbed some interesting (at least for me :-) side of prunning.
Namelly, what happens when a trunk is not running VTP in a switch that
has prunning enabled.
Seems to be the case that the switch requests all allowed vlans as being
connected, so if you don't configure the allowed vlans in such a trunk,
you will be effectivelly disabling much of the prunning.
BTW, prunning is SLOW and the switch will only requests the vlans when
the trunk is up, so after the trunk comes up, it takes a while for the
traffic to flow.
This, IMHO, makes the solution guide answer to IEWB lab 2 wrong for
point 1.4, because SW1 fast0/6 is a non VTP trunk carrying only vlans 6
and 26 but allowed vlans are not configured, so traffic on e.g. vlan 52
of SW2 will be flooded to SW1.
Brian McGahan wrote:
> John,
>
> Use "show interface fastethernet0/13 pruning" to see what is
> being pruned.
>
> Pruning does not have any affect when you are in transparent
> mode, as the transparent switch's VLAN database is only locally
> significant. The reason that you would edit the "switchport trunk
> pruning" list (called the prune-eligible list) is to stop certain VLANs
> from being pruned.
>
> By default, all standard VLANs (2-1001) are prune-eligible.
> This means that a pruning message can be sent for these VLANs. If for
> some reason you do not want a VLAN to be pruned, remove it from the
> prune-eligible list by issuing the "switchport trunk pruning" command on
> the appropriate trunk link.
>
>
> HTH,
>
> Brian McGahan, CCIE #8593
> bmcgahan@internetworkexpert.com
>
> Internetwork Expert, Inc.
> http://www.InternetworkExpert.com
> Toll Free: 877-224-8987 x 705
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>
>
>>-----Original Message-----
>>From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
>
> Of
>
>>John Michalek
>>Sent: Monday, August 09, 2004 7:36 AM
>>To: ccielab@groupstudy.com
>>Subject: 3550 VTP pruning
>>
>>I have a 3550 (CATA) configured as a VTP server and a 3550 (CATB)
>>configured
>>as a VTP client.
>>I then enable VTP pruning on the VTP server using the "vtp pruning"
>>command.
>>The VTP server is also the root for VLAN 10, 20, 30, 40 ,50.
>>I'm using fa0/13 as the trunk port.
>>
>>1) How do I verify that vtp pruning is actually working.
>>When I issue the "show interface trunk" on either ther VTP server or
>
> the
>
>>VTP client I get the following information:
>>
>>CATA#sh int trunk
>>
>>Port Mode Encapsulation Status Native vlan
>>Fa0/13 on 802.1q trunking 1
>>
>>Port Vlans allowed on trunk
>>Fa0/13 1-4094
>>
>>Port Vlans allowed and active in management domain
>>Fa0/13 1,10,20,30,40,50
>>
>>Port Vlans in spanning tree forwarding state and not pruned
>>Fa0/13 1,10,20,30,40,50
>>
>>CATB#sh int trunk
>>
>>Port Mode Encapsulation Status Native vlan
>>Fa0/13 on 802.1q trunking 1
>>
>>Port Vlans allowed on trunk
>>Fa0/13 1-4094
>>
>>Port Vlans allowed and active in management domain
>>Fa0/13 1,10,20,30,40,50
>>
>>Port Vlans in spanning tree forwarding state and not pruned
>>Fa0/13 1,10,20,30,40,50
>>
>>
>>2) why does the "show interface trunk" show that VLAN 10,20,30,40,50
>
> are
>
>>not
>>pruned?
>>
>>3) do I only use the "switchport trunk pruning" command when I'm
>
> using
>
>>VTP
>>transparent?
>>My understanding is that if a vlan is pruning ineligible it will not
>
> be
>
>>pruned from the trunk and that using the "switchport trunk pruning"
>>command
>>will change the pruning eligble list.
>>Is that correct?
>>
>>
>
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-- Carlos G Mendioroz <tron@huapi.ba.ar>
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