From: Gustavo Novais (gustavo.novais@novabase.pt)
Date: Thu May 24 2007 - 14:34:53 ART
I agree with you, the problem is that I cannot change or activate
pruning, as it is not my network.
My doubt is just that I cannot find any specific info confirming that
behaviour, as it results of not-so-good design in my opinion, but that
happens to work.
Thanks
Gustavo Novais
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Mohammad Saeed
Sent: quinta-feira, 24 de Maio de 2007 18:16
To: Cisco certification
Subject: Re: Question about 802.1q trunking - Do not have any switch
near to test...
In my opinion, as no Pruning is in place, all VLANS will be allowed on
trunk link and flooded traffic from all VLANS will pass through the
trunk even if the respective VLAN does not exist on the other switch.
So, if that VLAN does not exist on the other switch traffic will
dropped. This is where Pruning comes, if you want to let the traffic
pass on the trunk only for the VLANS that exist on the other end,
enable VTP pruning on both switches.
By default 802.1Q trunk tag all VLANS traffic except the Native VLAN,
so as per this rule, if traffic is flooded in VLAN 10, suppose, when
it will cross the Dot1Q trunk it shall be tagged with the respective
VLAN ID, VLAN 10, so that receiving switch shall be able to contain
the traffic in the VLAN 10.
Hope this helps.
Regards,
Mohammad Zahed Saeed
On 5/24/07, Gustavo Novais <gustavo.novais@novabase.pt> wrote:
> Hello,
>
>
>
> Lately I faced a doubt while on a customer audit, that although does
not
> affect performance, has left me thinking...
>
>
>
> You have two switches (lets say 3550 and 2950) in VTP mode
transparent,
> interconnected through a dot1q trunk, without any vlan filtering on
the
> trunk ports, but both switches have different vlan databases. Some
vlans
> in common, some not.
>
>
>
> What will happen to the flooded traffic on those trunk ports on the
> not-in-common (nic) vlans?
>
>
>
> Sh interface trunk tells me that not-in-common vlans are STP
forwarding
> and are obviously allowed on the trunk.
>
>
>
> Will the flooded traffic for one of those vlans cross the patch cable
> (tagged), and be dropped by the other switch, who doesn't know that
vlan
> ID?
>
> Or will it simply not be forwarded over that particular link?
>
> Or will it be flooded through the trunks native vlan (on the receiving
> switch)?
>
>
>
> Any ideas/comments/links pointing to info are helpful.
>
>
>
> Thanks
>
>
>
> Gustavo Novais
>
> #15622
>
>
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