Trunk Problem between Switches.

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May 30th, 2008
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I have attached Network Diagram as well as Config of each device involved.

I am not able to Ping from R2 or a PC if connected in that Switch Port Fa0/8.Similarly i am not able to Ping from R1 - 7206.

Please suggest.

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n.nandrekar Fri, 05/30/2008 - 04:29
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Config looks absolutely fine. Do you have any additional config / paths than what you have provided? Can you enable " debug ip icmp" on both the routers and see what messages you are getting?

1. Ensure links are up.

2. Verify the vlans are correctly assigned to the ports.

3. Look at the counters and see where the packets are dropped ( on which device).



sushilpandita78 Sun, 06/01/2008 - 21:26
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no i don't have any other config.

i would like to mention one thing here that i have already one vlan working on this switch and it is working absolutely fine without any issues.All the related ports are up.

glen.grant Fri, 05/30/2008 - 07:24
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Did you create the layer 2 vlans for vlan 35 on the 3560's in the middle of this setup ?

sushilpandita78 Sun, 06/01/2008 - 21:13
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No i didn't create using any interface vlan commands.I just assigned Port to this particular VLAN and it got created automatically.

bvsnarayana03 Sun, 06/01/2008 - 21:28
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yes, if you dont have a vlan & you assign port to a particular vlan than it gets created automatically.

Regarding your case, are all the trunk links up? "sh int trunk"

Did you check pinging hop by hop. i.e. ping switch 1 1st then switch 2 & finally router. Similarly repeat this from the other router. this would help get to the device having problems.

n.nandrekar Sun, 06/01/2008 - 22:20
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I am not sure if it creates the vlan automatically. Atleast not in c6500. Can you provide the show commands for the vlans and spanning tree?

Sh vlan id xx and sh spanning tree vlan xx...

It will give an idea of whether the vlan is created or not.

Second thing is check the mac-address-table on the switches to see till where the frames are travelling. If you see via the counters that packets are sent out of the router but not learnt on the switch mac table, chances are that your vlans are not active and the packets dropped on ingress.



sushilpandita78 Mon, 06/02/2008 - 23:23
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now working.

actuall that vlan 35 was not showing in Switch-1 when i checked it with sh vlan command.

i then created vlan 35 in witch-1 by issuing command vlan 35 in global config mode.

it means when ever i have to assign a port to a new vlan in Switch-2 i will need to create it in Switch-1 also then only can i communicate end to end through that Vlan.

is this the correct way or there is some other way out also.please suggest.

Rick Morris Tue, 06/03/2008 - 05:22
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Please see my other post.

It explains VTP Domain and setting one up as a server and the other as a client.

Then you will only need to create it one time and it will propigate to all other switches in the domain in client state.

raj_ctech1103 Mon, 06/02/2008 - 05:04
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Can u provide the full configuration of the devices.


Raj Kumar

Rick Morris Mon, 06/02/2008 - 07:08
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couple of things to check.

1. Verify the interfaces are up/up

2. On the switch verify the VLAN is in the database.

3. Ping the router ip

4. Verify the interface the PX is plugged in is up/up

From router:

sh ip int br

From switch:

sh ip int br

We are looking for the interfaces we are dealing with to make sure they are active.

From switch:





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