VLAN IDs/Headers

[TimOnCisco]

Hi Guys!

I'm working my way through the ICND2 book in preparation for taking the CCNA exam.

Chapter three deals with troubleshooting and the bit I'm concerned with is at the top of p149 (if you have access to it).

The text states: "... both SW1's trunks use 802.1Q, with native VLAN 1, so SW1 will add an 802.1Q header, with VLAN ID 3, to each copy of the broadcast frame..."

The issue I have is, for VLAN 1 why is would the VLAN ID be 3?

I looked back at pages 11 & 12, which seem to confirm that VLAN 1 should have a VLAN ID of 1, and VLAN 2 a VLAN ID of 2.

Is this just a typo on page 149, or have I missed something important about the way VLAN IDs are created/assigned?

Tim

[Kevin P Sheahan]

Sounds like a typo to me. Vlan 1 actually will not have a 802.1Q header applied to it because it is the native vlan and will traverse the link untagged. The other vlans will be tagged respectfully as you've stated with vlan 2 being tagged with vlan id 2 and so on.

Cisco Press offers some outstanding study material, but you will find typos in almost every release. Pat yourself on the back for challenging it though! Sometimes I think they do that on purpose to keep you on your toes

Kind Regards,

Kevin

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[TimOnCisco]

Kevin,

thanks for getting back to me.

Having read, and re-read, the relevant chapter again, I would be inclined to agree with you, but (and I'm now sorry for this!) I realise now that I didn't include enough about the situation.  My bad, but at least it got me to read, and re-read the text.

The section is actually dealing with a broadcast in VLAN 3.  Although the native VLAN is 1, the VLAN ID of 3 is needed to ensure that the broadcast remains within the correct VLAN.

So, to conclude, the book is (of course) right.

I just wish that I'd figured it out sooner.  The trouble is, sitting at home with a book doesn't give you anyone else knowledgable to discuss matters with. You just end up talking to yourself, and that doesn't always lead to a useful conclusion, regardless of how much you might agree with yourself!

Thanks again.

Tim