From: ccie2be (ccie2be@nyc.rr.com)
Date: Fri Nov 19 2004 - 13:53:44 GMT-3
Hi Bob,
Your answer to this (very old) post was specific to 802.1q trunks. Would
your answer be any different if ISL trunks were being used instead?
TIA, Tim
----- Original Message -----
From: "Bob Sinclair" <bsin@cox.net>
To: <jfaure@sztele.com>; <ccielab@groupstudy.com>
Sent: Saturday, November 29, 2003 7:50 PM
Subject: Re: Catalyst 802.1q trunking issues
> Juan,
>
> I put a sniffer on a 3550 dot1q trunk and observed the following when I
> removed Vlan 1 from the dot1q trunk, but left it as the native vlan:
>
> 1. All traffic leaving the port is tagged
> 2. VTP, CDP and DTP traffic leave the port with Vlan 1 tags
> 3. No other Vlan 1 traffic is seen leaving the port (including no Vlan 1
> BPDUs)
> 4. All BPDUs are PVST+ encapsulated, to address 01-00-0c-cc-cc-cd
>
> This should not cause a problem as long as all of your switches are Cisco
> and similarly configured:
> a. The Cisco switches recognize that CDP, VTP and DTP are not to be
> forwarded
> b. The Cisco switches recognize the encapsulated BPDUs
>
> You very well might have an STP issue if you connect such a port to a
> non-Cisco switch, because the brand X switch will not see any recognizable
> BPDUs, and the Cisco switch may not recognize the untagged BPDUs on the
> native vlan coming from the Brand X switch. It would seem prudent to
allow
> the native vlan across the trunk.
>
> But then, you would never put a Brand X switch in your network...
>
> would you?
>
> -Bob Sinclair
> CCIE #10427, CISSP, MCSE
> bsinclair@netmasterclass.net
>
>
> ----- Original Message -----
> From: <jfaure@sztele.com>
> To: <ccielab@groupstudy.com>
> Sent: Saturday, November 29, 2003 12:55 PM
> Subject: Catalyst 802.1q trunking issues
>
>
> > Hi all:
> >
> > -From the 6500 CCO configuration guide, about removing vlan1 from the
> > trunk:
> >
> > "You can remove VLAN 1. If you remove VLAN 1 from a trunk, the trunk
> > interface continues to send and receive management traffic, for example,
> > Cisco Discovery Protocol (CDP), VLAN Trunking Protocol (VTP), Port
> > Aggregation Protocol (PAgP), and DTP in VLAN 1. "
> >
> > -But also, in the same document:
> >
> > "Disabling spanning tree on the native VLAN of an 802.1Q trunk without
> > disabling spanning tree on every VLAN in the network can cause spanning
> > tree loops. We recommend that you leave spanning tree enabled on the
> native
> > VLAN of an 802.1Q trunk. If this is not possible, disable spanning tree
on
> > every VLAN in the network. Make sure your network is free of physical
> loops
> > before disabling spanning tree"
> >
> > And then my question is:
> > If you have several dot1q trunks configured in your swiched network in
> such
> > a way that these trunks don't allow pass the vlan1, the vlan1 is the
> native
> > vlan for them (you can see this doing a "sh int trunk") and the
interface
> > vlan 1 is in shutdown state in all the switches (but no STP disabled on
> > this vlan 1), can you have any stp issues like to be unable to block
some
> > loops?
> > What happens with the STP control traffic if vlan 1 isn't included on
the
> > trunks? Having vlan 1 in shutdown state maybe interpreted by the system
as
> > it has stp disabled for this vlan? I'm usign RAPID PVSTP
> >
> > Any thoughs will be greatly apreciated.
> >
> >
> >
> >
> >
> > Juan Faure Ferrer
> > email: jfaure@sztele.com
> >
> > Lmnea de Negocio de Telematica y CC
> > Ingeniero de Integracisn de Redes y Sistemas
>
> --------------------------------------------------------------------------
> --
> >
> > SOLUZIONA TELECOMUNICACIONES
> > Servicios Profesionales de UNION FENOSA
> > Jerez, 3
> > 28016 MADRID
> > tel 91 579 30 00 fax 91 350 72 83
>
> --------------------------------------------------------------------------
> -
> >
> > _______________________________________________________________________
> > Please help support GroupStudy by purchasing your study materials from:
> > http://shop.groupstudy.com
> >
> > Subscription information may be found at:
> > http://www.groupstudy.com/list/CCIELab.html
>
> _______________________________________________________________________
> Please help support GroupStudy by purchasing your study materials from:
> http://shop.groupstudy.com
>
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html
This archive was generated by hypermail 2.1.4 : Thu Dec 02 2004 - 06:57:47 GMT-3