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Re: VTP and ISL and 802.1q trunks posted 09/12/2003
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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.



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

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.


----- Original Message ----- From: "MADMAN" <dmadlan@xxxxxxxxx> To: "ccie2be" <ccie2be@xxxxxxxxxx> Cc: "Group Study" <ccielab@xxxxxxxxxxxxxx> 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.


ccie2be wrote:


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


Example 2: Assume Sw1 is VTP server and sw2 and sw3 are VTP clients all


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


test valid config's even if they're not good config's.

Thanks, dt

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"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"