From: ccie2be (ccie2be@nyc.rr.com)
Date: Sat Sep 13 2003 - 18:25:08 GMT-3
Hi Lee,
Thank you again. If I had a couple of 3550's I would definately try this
myself - afterall cisco has 2 of them in the lab and I suspect that they're
back to back ( the better to test more switching features ), so I'm
expecting Cisco to try to nail us candidates with stuff like that.
I've got one more scenario that I think is really interesting - more from an
academic point of view than because I think I'd see this on the lab.
sw1 ---trunk---fa0/0 router fa0/1 ---trunk --- sw2
On the router, fa0/0 and fa0/1 are BRIDGED together, assume vlan 1 is
running over both trunks and sw1 is a vtp server and sw2 is a vtp client.
What happens to vtp frames when they reach the router? Does the router
forward the frames back and forth from one trunk to the other? Will sw2, as
a vtp client, learn the same stuff as it would if the router were an actual
switch? Would the answers to the above questions depend on whether both
trunks are running the same trunking protocol? or a particular trunking
protocol?
Although I've looked, I haven't found any vtp commands that I can use on the
router to make it a member of the vtp domain and therefore I can't figure
out what the router does with vtp frames and what the impact of the above
config is.
As I said, I'm not concerned about this as a practical matter. But, I think
the above questions are really interesting. How bout you?
dt
----- Original Message -----
From: "Carter, Lee" <Lee.Carter@CommerceBank.com>
To: "'ccie2be'" <ccie2be@nyc.rr.com>; "Carter, Lee"
<Lee.Carter@CommerceBank.com>
Sent: Saturday, September 13, 2003 4:50 PM
Subject: RE: VTP and ISL and 802.1q trunks
>
> If you have a configuration like this:
>
> -------- --------
> | | | |
> | 6509 |<<------ISL------>>| 6509 |
> | | | |
> | | | |
> | |<<-----Dot1.q---->>| |
> | | | |
> -------- --------
>
> Obviously these can't be part of a channel group since they are using
> different encapsulation methods but you can configure something like
> uplinkfast for faster redundancy failover.
>
> I would have to set up this scenario before I could give you any definite
> answers as to what to look out for. I would mention the usual and look for
> layer 2 loops.
>
> Pick a vlan and start on one of the for ports above and look to see if
that
> vlan is in forwarding or blocking state (one of the four MUST be in
blocking
> or you have a loop)
>
> For 'sudo' load balancing you can spanning-tree priorities and change the
> default behavior of the layer 2 path. Or to be safe (but you loose
> redundancy) you can send only certin VLANs down one link and other VLANs
> down another (but again, this is a bad design because you would lose all
> redundancy. If one of the links fails half of your vlans (what ever you
> configure) will not trunk!
>
> I'll keep this e-mail in my inbox and if I get time I'll try this scenario
> and see if I find any little got-ya's.
>
>
>
>
>
> -----Original Message-----
> From: ccie2be [mailto:ccie2be@nyc.rr.com]
> Sent: Saturday, September 13, 2003 1:50 PM
> To: Carter, Lee
> Subject: Re: VTP and ISL and 802.1q trunks
>
> Hi Lee,
>
> Thank you for taking the time to get back to me on this. Your response is
> the only one that comprehensively answered my question and I very much
> appreciate that.
>
> Maybe I'm over reaching but is there any chance that, if you know, you
could
> answer any of the other questions below, especially the one about 2 Cat's
> connected back to back by 2 trunks - 1 using ISL and the other using
802.1q.
>
> As I mentioned, I don't think there would be any problems with doing that
> but the one thing I do know is that Cisco is incredible in coming up with
> odd ball topologies that excel at exposing any weakness one has.
>
> Thanks again, dt
>
>
> ----- Original Message -----
> From: "Carter, Lee" <Lee.Carter@CommerceBank.com>
> To: "'MADMAN'" <dmadlan@qwest.com>; "ccie2be" <ccie2be@nyc.rr.com>
> Cc: "Group Study" <ccielab@groupstudy.com>
> Sent: Saturday, September 13, 2003 1:55 PM
> Subject: RE: VTP and ISL and 802.1q trunks
>
>
> > To answer the first question below:
> >
> >
> > SW1 --- (ISL) ---- SW2 ---- (DOT1.Q) ----- SW3
> >
> > (server) (client) (client)
> >
> > same vtp domain.
> >
> > Yes this configuration works just fine. The only special consideration I
> can
> > think of (but you wouldn't see this on the lab)..
> >
> > SW1 - Cisco Device (has to be (ISL)
> > Sw2 - Cisco Device (has to be (ISL)
> > SW3 - NON Cisco device (like some bay piece of @!@#$%)
> >
> > The Dot1.q trunk link between SW2 and SW3 will only have one instance of
> > vlan spanning tree for any and all vlans that are trunked across it. If
a
> > single vlan were to bounce on SW3 it would send one TCN (topology change
> > notification) to Sw2 without a specific VLAN (since it does not support
> per
> > vlan spanning-tree) SW2 would then send out a TCN for each and every
vlan
> to
> > SW1 since it does not know which vlan bounced on SW3. (I have seen this
in
> 3
> > different large networks and this has caused serious layer 2 outages).
> >
> > My suggestion to fix this would be to run a layer 3 link between SW2 and
> SW3
> > and stop the trunking or to use the same vendor throughout.
> >
> >
> > -----Original Message-----
> > From: MADMAN [mailto:dmadlan@qwest.com]
> > Sent: Friday, September 12, 2003 3:34 PM
> > To: ccie2be
> > Cc: Group Study
> > Subject: Re: VTP and ISL and 802.1q trunks
> >
> > I know I have both encap types on the same swithes in the lab and
> > some customers have both encaps, ISL from legacy days and 802.1q cause
> > some platforms only support dot1q.
> >
> > I can't honestly say I recall a setup as you describe but I think it
> > would work. Would I do this for a customer, no.
> >
> > HTH
> >
> > Dave
> >
> > ccie2be wrote:
> >
> > > Hey Dave,
> > >
> > > Thanks for getting back to me.
> > >
> > > Are either of the below scenarios, scenarios that you've actually
> > > implemented and know from 1st hand knowledge?
> > >
> > > If you were able to implement the 1st scenario, did you do any vlan
load
> > > balancing between the 2 switches, for example, make sw1 the root for
> vlan
> > > 1,3, and 5 and make sw2 the root for vlan 2,4, and 6.
> > >
> > > Also, I've got one more interesting scenario regarding VTP and
trunking.
> > >
> > > Sw1 -----ISL trunk------router--------802.1q trunk----------Sw2
> > >
> > > Assume Sw1 is a VTP server and Sw2 is a VTP client. On the router,
the
> 2
> > > fast ethernet interfaces are bridged together. Q? Do VTP frames
> transit
> > > the router from Sw1 to Sw2 and enable Sw2 to be in the same VTP domain
> as
> > > Sw1?
> > >
> > > Q? If this doesn't work when the 2 trunks are different, like above,
> will
> > > it work if the 2 trunks are ISL? 802.1q?
> > >
> > > As you say, in a production network, it would be better for both
trunks
> to
> > > be the same, but Cisco doesn't care about that in the lab.
> > >
> > > dt
> > >
> > >
> > > ----- Original Message -----
> > > From: "MADMAN" <dmadlan@qwest.com>
> > > To: "ccie2be" <ccie2be@nyc.rr.com>
> > > Cc: "Group Study" <ccielab@groupstudy.com>
> > > Sent: Friday, September 12, 2003 12:57 PM
> > > Subject: Re: VTP and ISL and 802.1q trunks
> > >
> > >
> > >
> > >> no though I tend to use 802.1q, try to keep configs consistant.
> > >>
> > >> Dave
> > >>
> > >>ccie2be wrote:
> > >>
> > >>
> > >>>Hi,
> > >>>
> > >>>Are there any problems or issues when both ISL and 802.1q trunks are
> > >
> > > used in
> > >
> > >>>the same VTP domain?
> > >>>
> > >>>For example, suppose the following:
> > >>>
> > >>> ----ISL trunk --------
> > >>>Sw1 Sw2
> > >>> ----802.1q trunk----
> > >>>
> > >>>Is the above a valid configuration? If so, do any special
precautions
> > >
> > > need to
> > >
> > >>>be taken related to STP or VTP because one trunk is ISL but the other
> > >
> > > one is
> > >
> > >>>802.1q?
> > >>>
> > >>>
> > >>>Example 2: Assume Sw1 is VTP server and sw2 and sw3 are VTP clients
> all
> > >
> > > in
> > >
> > >>>the same VTP domain.
> > >>>
> > >>>
> > >>>Sw1----ISL trunk--------Sw2-------802.1q trunk--------Sw3
> > >>>
> > >>>Is this a valid configuration? Any gotcha's I need to be aware of?
> > >>>
> > >>>I know that these aren't preferred configs but the Cisco lab is
reputed
> > >
> > > to
> > >
> > >>>test valid config's even if they're not good config's.
> > >>>
> > >>>Thanks, dt
> > >>>
> > >>>
> >
>>>_______________________________________________________________________
> > >>>You are subscribed to the GroupStudy.com CCIE R&S Discussion Group.
> > >>>
> > >>>Subscription information may be found at:
> > >>>http://www.groupstudy.com/list/CCIELab.html
> > >>>
> > >>
> > >>--
> > >>David Madland
> > >>CCIE# 2016
> > >>Sr. Network Engineer
> > >>Qwest Communications
> > >>612-664-3367
> > >>
> > >>"Emotion should reflect reason not guide it"
> > >>
> > >
> > >
> > >
> >
> > --
> > David Madland
> > CCIE# 2016
> > Sr. Network Engineer
> > Qwest Communications
> > 612-664-3367
> >
> > "Emotion should reflect reason not guide it"
> >
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This archive was generated by hypermail 2.1.4 : Wed Oct 01 2003 - 07:24:27 GMT-3