VTP vs. 802.1q

Okay, I'm probably asking something that many of you may laugh at, but here it goes...

I'm reading through Odom's book for ICND2 and he seems to be saying that VTP and 802.1q (and ISL) are different without clarifying why.

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alan2308

802.1q and ISL are trunking protocols, which allow VLAN's to span multiple switches. The VLAN's can be configured on each switch individually, or they can be copied from switch to switch automatically.

VTP is a (poorly named) protocol which lets you configure VLAN's on one switch and that information is copied to all the other switches participating in the same VTP domain.

veritas_libertas

alan2308 wrote: »

802.1q and ISL are trunking protocols, which allow VLAN's to span multiple switches. The VLAN's can be configured on each switch individually, or they can be copied from switch to switch automatically.

VTP is a (poorly named) protocol which lets you configure VLAN's on one switch and that information is copied to all the other switches participating in the same VTP domain.

That sounds like the same thing. Sorry, I'm a tad confused by this concept.

alan2308

veritas_libertas wrote: »

That sounds like the same thing. Sorry, I'm a tad confused by this concept.

After re-reading my post, I agree. I'll try again a different way.

Let's say that you have two hosts, PC-A and PC-B that are in the same VLAN, but connected to different switches. 802.1q and ISL connect the switches in a way that allow PC-A and PC-B to communicate as if the were plugged into the same switch. It also allows for a switch to connect to a router while all traffic on the correct VLAN.

VTP really has nothing to do with trunking (hence my comment that it's a horribly named protocol). What VTP does is allow switches to send their VLAN database to other switches. It doesn't have anything to do with communication within a VLAN, it just information about VLAN's to other switches. Let's say you plug a brand new switch into another switch that is participating in VTP. All of the existing VLANs will now appear on the new switch.

thehourman

veritas_libertas wrote: »

That sounds like the same thing. Sorry, I'm a tad confused by this concept.

[SW1]

[SW2]
------\

\--/

[SW3]
Lets assume that we have 3 switches, like in the topology above. And all the switches are in the same VTP domain.
SW1 is the VTP server, and the other two are VTP clients.
The admin on SW1 created VLAN2. The new VLAN2 will be delivered to the other 2 switches, which are SW2 and SW3, by VTP. Meaning, SW2 and SW3 will automatically learn the new VLAN2 without the admin going to the switches.

veritas_libertas

So if I understand this correctly:

It's really dynamic vs static input of VLANs? I'm also gathering from this thread that VTP is not a protocol and only allows for VLANs to be dynamic?

thehourman

veritas_libertas wrote: »

So if I understand this correctly:

So it's really dynamic vs static input of VLANs? I'm also gathering from this thread that VTP is not a protocol and only allows for VLANs to be dynamic?

[R1](fa0/0)

(fa0/12)[SW1](fa0/1)

(fa0/2)[SW2]

((fa0/2)\

/(fa0/1)

\---/

(fa0/1)[SW3](fa0/2)
802.1q is a trunking protocol.
Lets use the same diagram above again. Lets say we have vlan1, 2, 3, 4, 5, 6, 7, 8, 9, and 10.
R1's fa0/0 is connected to SW1's fa0/12. SW1's fa0/1 is connected to SW2's fa0/2, and SW1's fa0/2 is connected to SW3's fa0/1. SW2's fa0/1 is connected to SW3's fa0/2. Those ports are in trunk mode, which is either 802.1q or ISL.

Now, you know since all the switches have all the VLANs (thanks to VTP), what the trunk does it lets all the vlans to travel from switch to switch with just one connection instead of one connection per vlan. It would be a waste of ports if we are going to use one connection per vlan.

Now, if a vlan wants to communicate to other vlans, it will use R1's fa0/0 and then R1's will forward the back the frame to its fa0/0 to the destination vlan. Also, R1's would use sub-interfaces for each vlan as their default-gateway.

alan2308

Let me try another way.

802.1q and ISL are concerned with traffic within VLANs, VTP is concerned with traffic about VLAN's.

Here's another scenario. PC1 is connected to SW1. PC2 is connected to SW2. PC1 and PC2 are both within the same VLAN (let's say VLAN10), and therefore both on the same subnet (I'll just leave routers out of this for now). Since the two PC's are on the same subnet, they should be able to communicate with one another (despite which switch they're physically connected to). In order to do so, the traffic crosses the 802.1q trunk. The trunk allows the PC1 and PC2 to talk to each other, and any other hosts within VLAN10 while at the same time, keeping that traffic segregated from any other VLAN. The traffic for every VLAN is able to cross that trunk, but it's tagged so every switch that sees it will know which VLAN it belongs to.

In this same scenario, let's say that you set up VLAN 10 on SW1. VTP will then let SW1 tell SW2 that VLAN10 now exists.

Edit: and don't worry, it's not as difficult in practice as it is to try to explain.

veritas_libertas

alan2308 wrote: »

Let me try another way.

802.1q and ISL are concerned with traffic within VLANs, VTP is concerned with traffic about VLAN's.

Here's another scenario. PC1 is connected to SW1. PC2 is connected to SW2. PC1 and PC2 are both within the same VLAN (let's say VLAN10), and therefore both on the same subnet (I'll just leave routers out of this for now). Since the two PC's are on the same subnet, they should be able to communicate with one another (despite which switch they're physically connected to). In order to do so, the traffic crosses the 802.1q trunk. The trunk allows the PC1 and PC2 to talk to each other, and any other hosts within VLAN10 while at the same time, keeping that traffic segregated from any other VLAN. The traffic for every VLAN is able to cross that trunk, but it's tagged so every switch that sees it will know which VLAN it belongs to.

In this same scenario, let's say that you set up VLAN 10 on SW1. VTP will then let SW1 tell SW2 that VLAN10 now exists.

Edit: and don't worry, it's not as difficult in practice as it is to try to explain.

Okay, now that makes sense! Thanks for taking the time to explain this to me.

IRONMONKUS

What an excellent topic! I was trying to learn VLANs the other day and was tired of typing in every VLAN on every switch. I guess it's a good way of burning it into my memory. I'm going to have to read up on this VTP action as that might make it easier in building up, breaking down, building up, and breaking down test scenarios.

Technology1

I've also been trying to learn about VLANs and VLAN Trunks.

Very interesting topic how a VLAN Trunk is a point to point ethernet connection from a switch to a switch or a switch to a router that can carrry traffic from multiple VLANs simultaneously on the same line.

1 - 1005 (1 and 1002 - 1005 are reserved)

Extended VLANs (1006 - 4094)

VTP Pruning

Server, Client, Transparent mode. From what I read, all cisco switches are intially configured as VTP servers.

Very interesting information to learn about VLANs and Trunks.

IRONMONKUS wrote: »

What an excellent topic! I was trying to learn VLANs the other day and was tired of typing in every VLAN on every switch. I guess it's a good way of burning it into my memory. I'm going to have to read up on this VTP action as that might make it easier in building up, breaking down, building up, and breaking down test scenarios.

seekrit

Just some quick clarifyers..

VTP is what is called a switch management domain protocol. It allows you to have a centralized management point for all of the VLANS within a single broadcast domain.
There are a lot of little quarks about VTP that can make it confusing to learn, like how Vlan data base information is stored on each mode (server, client, transparent).
VTP also exclusively uses VLAN1 even if you prune it from doing so in VTPv3.

802.1q and ISL will differ on how they handle VLAN tags. 802.1q uses something called native vlan over a trunk.. It's had slightly less frame overhead becasue it only uses 4bytes tag inside of a frame header. ISL encapsulates itself around a frame.

greenerek

8021q-this is a Trunk which u can use when u use cisco switches and different vendors(IEEE standard), whilst ISL is only cisco.However now the 8021q is more used

please find bellow

Configuring InterVLAN Routing and ISL/802.1Q Trunking on a Catalyst 2900XL/3500XL/2950 Switch Using an External Router - Cisco Systems

Willaynto

hello, i wanna to give one comment :
Function ISL 802.1Q
Defined by ISL Cisco -802.1Q IEEE
Inserts another 4-byte header instead of completely encapsulating the
original frame
ISL No- 802.1QYes
Supports normal-range (1–1005) and extended-range (1006–4094) VLANs
ISL Yes- 802.1Q Yes
Allows multiple spanning trees ISL Yes- 802.1Q Yes
Uses a native VLAN ISLNo -802.1Q Yes

Technology1

Very good article here about VLAN Tagging.

- The World's First Free Cisco Lab - Firewall.cx

Some other thoughts about VLANs:

VLANS do not have to be on the same switches but they are always in the same broadcast domain regardless of what switch a VLAN is on. Each VLAN can be on the same switch and they can also be on different switches. That's why they need VLAN Trunks to carry traffic from multiple VLANs simultaneousy on the same line.

You can think of a VLAN as a separate network that must have either a router or layer 3 switch to communicate with a different VLAN.

If you had 10 VLANS, traffic from all 10 can go over 1 trunk link instead of using 10 different ethernet cables and ports for each VLAN. That's the beauty of a VLAN Trunk.

Every VLAN must have a name and a number.

veritas_libertas wrote: »

Okay, I'm probably asking something that many of you may laugh at, but here it goes...

I'm reading through Odom's book for ICND2 and he seems to be saying that VTP and 802.1q (and ISL) are different without clarifying why.