vlan on dist switch n access switch puzzling me...

[cindylee27]

Hi Experts,

got one qn to ask u..it looks simple but doesn;t work to prove on the technically side.. I have created vlan 20 at access switch 2950 for one user, n this access switch is connected to 3750 which is Distribution switch. In turn, this distribution switch is connected to the core switch. The problem now is..user vlan 20 is not in the same vlan 20 as in core switch ip add range 10.36.20.254 255.255.255.0 until create another vlan 20 at the distribution switch.

Why does this happens? as the trunkings are suppose to span all VLANs across.. which in this case 3750 connected to 4506 is trunked..and 3750 connected to 2950 is also trunk..

very puzzling..

Another info is , 3750 has a domain vlan name and is a transparent mode n no password set.

interface vlan 20 : ip add 10.36.20.254 255.255.255.0

Vlan 20 Vlan 20

4506 --------------------------- 3750 ------------------------------------------ 2950 ----------------------- USer PC

gi0/1(trunk) gi2/0/1(trunk) fa0/1 (trunk) fa0/1 (trunk)

Thanks in advanced.

[cindylee27]

Thanks Paul..

Somehow it happened..due to history i presumed... ;)

well, "multi-homed" get into me now.. what is that actually ?

Well,am still lost..:) due to the "trunk" word as well..still dun get it why..

[Jon Marshall]

Cindy

Multi-homed just means you have more than one uplink between the switches so if you lose one of the connections you still have a path through your network.

If you are interested in changing to VTP server/client setup attached is a doc that will help you

http://www.cisco.com/en/US/tech/tk389/tk689/technologies_configuration_example09186a00807d5d42.shtml

HTH

Jon

[Jon Marshall]

Cindy

To try and answer you question.

If all switches are set to transparent mode then to have a vlan that spans your switches you will as Paul says have to create that vlan on all the switches.

Now lets say host A is on sw1 and in vlan 20.

Host B in sw2 and is in vlan 20.

Both switches are in VTP transparent mode and both switches have a vlan 20.

All switches in this example are connected via trunk links.

Host A wants to send a packet to Host B, gets the mac-address for host B, sends the packet which is switched across the trunk link and then delivered to Host B on the sw2.

Now lets say you add a switch in between sw1 and sw2, call it sw1a. On sw1a you do not have a vlan 20. If sw1a does not have a vlan 20 then in effect the vlan 20 on sw1 and the vlan 20 on sw2 are completely separate vlans. Neither sw1 nor sw2 see vlan 20 down the other end of the trunk link, they only see vlan 20 locally.

Only when you have actually created a vlan 20 on the sw1a have you in effect "joined" up the two isolated vlan 20's.

VTP server/client mode takes care of all of this for you.

Does this make sense ?

Jon

[paul.matthews]

By multi homed I mean you have two (or more) core switches so each distribution switch will link back to two core switches, at the next layer, each access switch also links back to two distribution switches, so that you have resilience for device or link failure.

See attached diagram as an example.

[cindylee27]

Thanks guys for all your input..post rated..

will try to digest..:)

[paul.matthews]

You are welcome.

Paul.

[cindylee27]

Guys,

sorry to bring up this issue but would like to get deep out of it on what is happening..I found some info from the switch..silly me..not sure if this could be the course of it..

VTP Version : 2

Configuration Revision : 0

Maximum VLANs supported locally : 1005

Number of existing VLANs : 44

VTP Operating Mode : Transparent

VTP Domain Name : LTTA

VTP Pruning Mode : Disabled

VTP V2 Mode : Disabled

VTP Traps Generation : Enabled

MD5 digest : 0x40 0xF5 0x0D 0xE3 0x5F 0xCA 0x1B 0x48

Configuration last modified by 136.121.10.101 at 0-0-00 00:00:00

The VTP Version 2 seems like disable..Could this be the reason which not able to propagate the vlan info across the trunk interface connected to core switches??

[paul.matthews]

Disabled means ignore the info but forward it. A switch in VTP mode transparent will not learn any VLANs vis VTP, so it could well be part of your problem.