From: Kenneth Wygand (KWygand@customonline.com)
Date: Thu Jan 15 2004 - 19:58:27 GMT-3
Hello everyone! Nice weather here in the Northeast!
I am trying to test out pruning between a 6509 and a 3550-24PWR.
1) Is there a command I can use the output from to determine if my VLANs
are being pruned properly? (both CAT OS on 6509 and IOS on
3500XL/3550-series)
2) If I have a port assigned on a switch for VLAN 10 (pruning enabled)
and the ports are up/down (administratively up, but nothing is plugged
in so the line protocol is down), should VLAN 10 be pruned until my
device becomes active on that port?
3) Is there any disadvantage (besides for VTP coding bugs) *NOT* to
enable global VTP pruning for every VLAN (if all devices support it, of
course)? I cannot think of a reason why not to make all networks more
efficient with this feature.
4) I've heard the maximum amount of VLANs you can run an instance of
spanning tree on is 64 within a 3500XL series switch. Since VTP pruning
does not disable spanning tree, I'm assuming that pruning does not
address this limitation.
5) Is there any problem with running 100 or so VLANs on a 3500XL switch
if a loop-free topology is ensured?
Thanks in advance!
Kenneth E. Wygand
Systems Engineer, Project Services
CISSP #37102, CCNP, CCDP, ACSP, Cisco IPT Design Specialist, MCP, CNA,
Network+, A+
Custom Computer Specialists, Inc.
"Real Engineers Debug in Binary."
-kw
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Brian McGahan
Sent: Wednesday, January 07, 2004 6:18 PM
To: 'Kurt Kruegel'; 'Rajagopal S'; 'phase90'; 'NathashaAleyevka';
ccielab@groupstudy.com
Subject: RE: Pruning!
Pruning stops the sending of broadcast and unknown unicast
frames
out trunk links. Unicast traffic is never a problem, because the CAM
table
knows which port to flood it to.
Suppose a frame comes into the switch destined for host X. The
switch looks in the CAM table to see what the outgoing interface is for
host
X. If there is an entry, it sends the frame out that interface. If
there
is not an entry, it sends the frame out all interfaces in that VLAN
(except
that which it was received on), including any trunk interfaces that are
forwarding that VLAN.
Broadcast traffic uses the same method. When a broadcast frame
comes in the switch sends the frame out all interfaces in that VLAN
(except
that which it was received on), including any trunk interfaces that are
forwarding that VLAN.
What pruning prevents is the sending of broadcast frames
(unknown
unicasts are effectively broadcast) by determining whether the adjacent
switch either has the VLAN in question locally assigned, or is in the
transit path for the VLAN. Suppose you have the following:
SW1---SW2---SW3
SW2 has trunk links to both SW1 and SW3. SW1 has VLANs 10, 20,
and
30 assigned, SW2 has VLAN 20 assigned, and SW3 has VLAN 30 assigned.
SW1 receives a broadcast (or unknown unicast) frame in VLAN 10.
Without pruning, this traffic will be forwarded to SW2, and SW2 will
forward
it to SW3. With pruning on, SW3 will send a prune message to SW2 for
VLAN
10. SW2 will in turn send a prune message to SW1 for VLAN 10. SW1 will
no
longer send SW2 broadcast traffic for VLAN 10.
SW1 receives a broadcast (or unknown unicast) frame in VLAN 20.
Without pruning, this traffic will be forwarded to SW2, and SW2 will
forward
it to SW3. With pruning on, SW3 will send a prune message to SW2 for
VLAN
20. Since SW2 has VLAN 20 assigned, it will report to SW1 that it has
it
assigned. SW1 will therefore forward broadcast traffic in VLAN 20 to
SW2,
but SW2 will not forward it on to SW3.
SW1 receives a broadcast (or unknown unicast) frame in VLAN 30.
Without pruning, this traffic will be forwarded to SW2, and SW2 will
forward
it to SW3. With pruning on, SW3 will send a prune message to SW2
reporting
that VLAN 30 is assigned. Although SW2 does not have VLAN 30 assigned,
it
is in the transit path for it. Therefore SW2 cannot send SW1 a prune
message for VLAN 30. SW1 will therefore forward broadcast traffic in
VLAN
30 to SW2, and SW2 will forward it on to SW3.
Regarding bugs in pruning, it's always a possibility. New
features
should always be put into a test environment before implementing them.
If
this is not possible you should at least check the bug toolkit for any
bugs
relating to the feature in question.
I *would* however recommend turning pruning on in your switch
block.
Pruning can significantly reduce the risk of a broadcast storm on an
isolated segment of the network bringing the entire switch block down.
HTH,
Brian McGahan, CCIE #8593
bmcgahan@internetworkexpert.com
Internetwork Expert, Inc.
http://www.InternetworkExpert.com
Toll Free: 877-224-8987
Direct: 708-362-1418 (Outside the US and Canada)
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
Of
> Kurt Kruegel
> Sent: Wednesday, January 07, 2004 12:38 PM
> To: Rajagopal S; phase90; Nathasha Aleyevka; ccielab@groupstudy.com
> Subject: Re: Pruning!
>
> pruning removes broadcast,unicast and unknown traffic on pruned vlans
from
> trunks ....
> simply because it's not there.
> without pruning all trunks carry all traffic at all times
>
> therefore trunks only carry that traffic to switches that particpate
in
> certain vlans.
> spanning tree remains ...
>
>
> ----- Original Message -----
> From: "Rajagopal S" <raj_ccie@yahoo.com>
> To: "phase90" <phase90@comcast.net>; "Nathasha Aleyevka"
> <naleyevka@yahoo.com>; <ccielab@groupstudy.com>
> Sent: Wednesday, January 07, 2004 12:02 PM
> Subject: Re: Pruning!
>
>
> > Hello Natasha,
> >
> > Pruning increases available bandwidth on a trunk ??
> >
> > Pruning basically reduces the VTP broadcasts on the trunk.. You
cannot
> remove traffic flowing on a trunk by pruning. You need to use access
lists
> in this case...
> >
> > use the command : vtp pruning on the global mode.
> >
> > YOu can also selectively prune the broadcasts on the trunk by the
> command
> : switchport trunk allowed vlan x,y,z on the trunk interface.
> >
> > Cheers
> > Raj
> >
> >
> > phase90 <phase90@comcast.net> wrote:
> > Nathasha,
> >
> > I would prune your trunks manually on as needed basis per
> > interface. Unless all your switches in you VTP domain are running
images
> > where the pruning code is stable, and proven
> > reliable, you could break your network. How do I know this? Because
it
> > happened to me once
> > although it was a while ago on some catalyst 6509s. I used the
global
> > command "set vtp pruning enable" and 1 of the switches had a bad
image
> in
> > it. This caused the vlan to break - dhcp and other
> > network services. Good Luck.
> >
> >
> >
> > Jerry
> > ----- Original Message -----
> > From: "Nathasha Aleyevka"
> > To:
> > Sent: Monday, January 05, 2004 5:23 PM
> > Subject: Pruning!
> >
> >
> > > Hi,
> > >
> > > I know that Pruning increases available bandwidth on a
> > > trunk link, now if I have to remove traffic from a
> > > VLAN that is not locally assigned to it, would I
> > > enable prunning(global configuration mode) on both
> > > sides of the link and be done with it.
> > >
> > > Is there any additional configuration needed to
> > > accomplish this?
> > > Thank you
> > >
> > >
> > >
> > >
> > >
> > > __________________________________
> > > Do you Yahoo!?
> > > New Yahoo! Photos - easier uploading and sharing.
> > > http://photos.yahoo.com/
> > >
> > >
>
This archive was generated by hypermail 2.1.4 : Mon Feb 02 2004 - 09:07:44 GMT-3