Frank,
Thanks for the explaination. That does help with the vlan issues. I also did
some more spelunking and found this at the Cisco site.
The following caveats have been resolved in Release 12.0(5.2)XU:
The software now supports frames larger than 1518 bytes. (CSCdr70758)
So maybe I was right in the fact that there might have been a code issue as
well???
Thanks,
Regards,
Steve Clevenger
Frank Wells wrote:
> When using ISL or 802.1q trunking, the sizes of the frames is only increased
> inside the switches. Once the frames exit the switches they are reduced back
> down to their original size by removal of the coloring info. If a frame
> must traverse multiple VLAN capable switches, each switch will reapply its
> own coloring info to the frame as it enters that switch and remove it as it
> leaves.
>
> In you are unfamiliar with the coloring concept, it is a way to describe how
> the VTP domain defines individual VLANs. By thinking of each VLAN as a
> color, it is helpful in understanding what is being done during the inter
> VLAN processes etc. Example: a switch receives a frame from VLAN 2 destined
> for VLAN 3, the switch identifies each VLAN as colors blue and red
> respectively. By adding a red field to the incoming VLAN 2 frame header it
> can easily identify the destination VLAN.
>
> This is a crude example of the frame tagging process but I hope it shed a
> little light.
>
> >From: srclevenger <[EMAIL PROTECTED]>
> >Reply-To: srclevenger <[EMAIL PROTECTED]>
> >To: Anthony Awatefe <[EMAIL PROTECTED]>
> >Subject: Re: Question about ISL and 802.1Q encapsulation
> >Date: Wed, 27 Sep 2000 14:28:00 -0700
> >
> >Anthony,
> >
> >I agree with you but have taken this a step further. If you have 802.1Q
> >tagging
> >applied to interfaces, Standard ports will not know what to do with it
> >because
> >it is tagged special (unless we are talking vlan aware / hybrid ports, then
> >they
> >take on both ends of the world in switching.) Therefore the packet drops at
> >a
> >standard port if not 802.1q aware. Right? Will you will see this as the
> >mini-giant? If it is aware of the 802.1q tag at each end will you not see
> >the
> >frame just pass thru the switch and not register the error? Could you have
> >a
> >code bug on the switch then if you see the pass thru 802.1q tag as an
> >error? I
> >understand that switches should adjust to different tags so that you do not
> >see
> >them as errors or have I been given a smoke screen? Could there be a
> >configuration error in the setup of the switch, ie a combo of the 802.1q
> >and
> >hybid?
> >Understand that this is the sort of thing I am still learning for the BCMSN
> >test
> >in October, so I maybe in the same boat as you are. So please let me know
> >what
> >you find out.
> >
> >regards,
> >Steve Clevenger
> >
> >
> >Anthony Awatefe wrote:
> >
> > > Normal Ethernet frames sizes can not exceed 1518 bytes. When 802.1q
> >tagging
> > > is used frame sizes can increased to a maximum of 1522 bytes. This is
> >known
> > > as a mini giant, switches have no problem handling these frame types,
> > > although it my register on the switch as an error.
> > >
> > > With ISL Encapsulation the switch identifiies the frame as an ISL frame
> >type
> > >
> > > Regards
> > > Anthony
> > >
> > > ----- Original Message -----
> > > From: "Dove" <[EMAIL PROTECTED]>
> > > Newsgroups: groupstudy.cisco
> > > To: <[EMAIL PROTECTED]>
> > > Sent: Wednesday, September 27, 2000 7:28 AM
> > > Subject: Question about ISL and 802.1Q encapsulation
> > >
> > > > Hi,
> > > >
> > > > I have a question about ISL and 802.1Q encapsulation/tagging. As I
> >know,
> > > ISL
> > > > will encapsulate a frame with adding 26 bytes to header and 4 bytes to
> > > > trailer; and 802.1Q will modify the existing header and add 4 bytes to
> >it.
> > > > My question is: if the frame is already in its maximum size (i.e.
> >1,518
> > > > byte), after ISL or 802.1Q encapsulation/tagging, the frame size will
> >be
> > > > greater than the ethernet maximum size. Will it cut the frame into 2
> >parts
> > > > or ignore the frame size checking?
> > > >
> > > > Regards.
> > > > dovelet
> > > >
> > > >
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