From: Salau, Yemi (yemi.salau@siemens.com)
Date: Fri Aug 31 2007 - 10:17:53 ART
Sure,
The definition of your flooded traffic will have to be
Broadcast/Multicast/Unknown Unicast Traffic before I can agree with you.
Ofcourse they don't achieve exactly same thing end result. Below are
excerpts from IEWB material:-
VTP pruning allows a switch to communicate with its directly connected
neighbors about what VLANs they have locally assigned and are in the
transit
path for. Therefore VLANs that are unnecessary can be "pruned" off of
the
interface. VTP pruning can be enabled by issuing the vlan database or
global
configuration command vtp pruning.
BUT Check this out:-
By default all VLANs are allowed to transit a trunk link. As previously
mentioned,
VTP pruning can automatically remove unnecessary VLAN traffic from a
trunk
interface. However, not all devices that support trunking also support
pruning.
This is the case when enabling router-on-a-stick with a Router to a
Switch.
Since a Router does not support the automatic removal of unnecessary
VLAN traffic,
unassigned VLANs must be manually removed from the interface by editing
the
'allowed' list. The allowed VLAN list, as the name implies, specifies
which
VLANs are allowed to transit a trunk link. To edit the allowed VLAN
list, issue to
switchport trunk allowed vlan interface level command.
NOW from CCO
(http://www.cisco.com/univercd/cc/td/doc/product/lan/cat3560/12225see/cr
/cli3.htm#wp1948736 and
http://www.cisco.com/univercd/cc/td/doc/product/lan/cat3560/12225see/scg
/swvtp.htm#wp1035139):-
Allowed List: Set the list of allowed VLANs that can receive and send
traffic on this interface in tagged format when in trunking mode.
VTP Pruning: VTP pruning increases network available bandwidth by
restricting flooded traffic to those trunk links that the traffic must
use to reach the destination devices. Without VTP pruning, a switch
floods broadcast, multicast, and unknown unicast traffic across all
trunk links within a VTP domain even though receiving switches might
discard them. VTP pruning is disabled by default.
From the Above analysis, shouldn't both vtp pruning and switchport trunk
allowed vlan will achieve the same thing for broadcast/multicast/unknow
unicasts?
REFERENCE
IEWB .... Version 3 by InternetworkExpert
CCO .... Cisco Systems
Many Thanks
Yemi Salau
________________________________
From: Ronnie Angello [mailto:ronnie.angello@gmail.com]
Sent: Friday, August 31, 2007 1:41 PM
To: Salau, Yemi
Cc: NET HE; thomas.rader@freesurf.ch; ccielab@groupstudy.com
Subject: Re: VTP Pruning
VTP pruning does not remove the VLAN from the trunk like pruning
manually with the switchport trunk allowed vlan command. It just
prevents flooded traffic from going over trunk links where the traffic
is not needed. Manually pruning VLANs from trunks actually removes the
STP instance for the VLAN from the trunk as well.
On 8/31/07, Salau, Yemi <yemi.salau@siemens.com> wrote:
Just to add to this in a lay-man language that I understand :-),
vtp-pruning is an automated implementation of vlan-allowed list
at trunk
boundaries. Basically, you're allowing/denying tagged frames as
they
come in on that port depending based on vlan_id. But the good
thing is,
I don't need to accept a tagged frame with a vlan_id which
doesn't exist
on the Switch, so I "prune" such as it's coming into that trunk
port.
Could do this via vlan-allowed list, but vtp prunning is the
automated
variation of doing this.
VTP Pruning is still useful these days, trust me.
Many Thanks
Yemi Salau
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On
Behalf Of
NET HE
Sent: Friday, August 31, 2007 2:52 AM
To: thomas.rader@freesurf.ch; ccielab@groupstudy.com
Subject: RE: VTP Pruning
Give you an example, then you will understand it.
Let's say there are 3 switches linked by trunks in a VTP domain,
switch1
as
vtp server, other 2 as vtp clients.
Switch1 has host A1, B1, C1 connected to VLAN 1, 2, 3
respectively,
switch2
has hosts A2, B2, C2 connected to VLAN 2, 3, 4 respectively, and
switch3
has
hosts A3, B3, C3 connected to VLAN 1, 2, 3 respectively
After a period of silence, A1 is trying to ping A3, A1 first
will send
an
ARP broadcast asking for MAC address of A3. If VTP pruning is
not on at
switch2, you will see ARP message on the trunk between switch1
and
switch2,
switch1 and switch3. But if VTP prunning is on at switch2,
switch2 has
already reported to switch1 saying that I don't have any hosts
at VLAN
1,
please don't send any VLAN 1 traffic to me. Therefore you will
only see
that
ARP message on the trunk between Switch1 and Switch3, not the
trunk
between
Switch1 and Switch2.
Best Regards,
Net (Xin) He
>Hello,
>
>I've never really understood VTP Pruning.
>
>Sure I know that it reduces VTP traffic and is enabled using
the "vtp
>pruning" syntax, but I've never seen this deployed in any
networks.
>
>Has anyone got any experiences with this or can share light on
this
matter
>?
>
>Thanks, Thomas
>
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