From: Bob Sinclair (bsin@cox.net)
Date: Wed Nov 26 2003 - 12:12:30 GMT-3
Sasa,
VTP and CDP will come out of the switch with Vlan 1 tags under this
scenario.
I redid the experiment with the following configuration on the 3550 running
12.1(19)EA1 EMI software. I connected the port to my PC runnning Sniffer.
1. trunk dot 1.q
2. native vlan 2
3. vlan 1 removed from trunk
4. vlan dot1q tag native
The results showed:
1. all frames coming out of the switch were tagged
2. VTP and CDP frames had vlan 1 tags
3. No other vlan 1 traffic came across the link: no vlan 1 broadcasts, no
vlan 1 bpdus.
4. DISL frames came tagged on the native vlan.
Hope that helps. I can send the sniffer capture offline if you want it.
-Bob Sinclair
CCIE #10427, CISSP, MCSE
bsinclair@netmasterclass.net
----- Original Message -----
From: "Sasa Milic" <smilic2@pexim.co.yu>
To: "Tasuka Amano Hsu" <tasuka@mac.com>
Cc: "ccielab Groupstudy" <ccielab@groupstudy.com>
Sent: Wednesday, November 26, 2003 8:58 AM
Subject: Re: Fwd: 3550 Switch VLAN native ?
> VTP, CDP etc. would you lowest numbered VLAN allowed on the trunk.
>
> Sasa
>
>
> Tasuka Amano Hsu wrote:
> >
> > Thanks Bob,
> > But if I disallow the VLAN 1, then the VTP still passthrough or not ?
> > I mean if disallow the VLAN, and native to other vlan, then the VTP
> > traffics will still at VLAN 1 or will change to native VLAN ?
> >
> > Sincerely,
> > Tasuka
> >
> > Begin forwarded message:
> >
> > > Tasuka,
> > >
> > > Looks to me like instruction 1 is pointing to VTP pruning.
> > >
> > > I think these instructions are telling us to allow only the listed
> > > vlans
> > > across the link. The 3550 will allow you to remove vlan 1 from a
> > > trunk, so
> > > I would do that and make another vlan native. CDP and VTP will come
> > > out
> > > with vlan 1 tags, but no other vlan 1 traffic will be seen.
> > >
> > > I guess #3 is talking about UDLD? Maybe someone else can help on this?
> > >
> > > Good catch on the "vlan dot1q tag native " command.
> > >
> > >
> > > Hope that helps,
> > >
> > > -Bob Sinclair
> > > CCIE #10427, CISSP, MCSE
> > > bsin@cox.net
> > >
> > >
> > > ----- Original Message -----
> > > From: "Tasuka Amano Hsu" <tasuka@mac.com>
> > > To: "ccielab Groupstudy" <ccielab@groupstudy.com>
> > > Sent: Friday, November 14, 2003 11:25 AM
> > > Subject: 3550 Switch VLAN native ?
> > >
> > >
> > >> Hi, my english not very well, so I need to make sure the I am
> > >> understand what it said:
> > >>
> > >> 1.If a downstream switch does not process a port in a VLAN that your
> > >> switch is advertising, you are responsible for making sure that your
> > >> switch does not propagate broadcast traffic for those VLANs.
> > >>
> > >> 2.Create VLANs 10,20,30,40,55,70 and 100. Name each VLAN; VLAN_A,
> > >> VLAN_B. etc.
> > >>
> > >> 3.Configure the two interfaces connecting the 3550's to appear as 1
> > >> link to STP, If either of the interface is damaged, both switches
> > >> should actively manage one-way links.
> > >>
> > >> 5.This link should allow all VLANs to travel across with their VLAN
ID
> > >> in tact. You can not use Cisco Proprietary protocol to archive this.
> > >> Every packet that traverses the link must have the VLAN ID, no
> > >> exceptions.
> > >>
> > >> 6.Only allow the defined VLANs across this link.
> > >>
> > >> So I will configure a port group with a 802.1q trunk mode and make
> > >> sure
> > >> that link has a native VLAN tag for un-tag traffic packets, but does
> > >> that mean I can use VLAN 1 ? or VLAN 10 as the native VLAN. and just
> > >> allow the define VLAN traffic passthrough the switch, does it need
> > >> include VLAN 1 ?
> > >>
> > >>
> > >> Sincerely,
> > >> Tasuka
> > >>
> > >>
This archive was generated by hypermail 2.1.4 : Fri Dec 12 2003 - 12:29:17 GMT-3