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connecting multiple networks with switches

Hello everyone,

We need your help to solve a network connection issue.

We need to connect multiple networks through three or four cisco 3560, 3750 switches.

I configured two 3750 stack switches with trunking on all Gig fiber ports and one on gi1/0/48 - fa0/43 3560 as one switch has no fiber ports, for network 1 on 10.1.1.0 network

I configured the two 3750 stack switches with trunking on all Gig fiber ports for our networks we plan to connect to this switch using Vlans and inter Vlan routing.

I was able to connect two networks for both 3750 stacks with a fiber cross over cable, adding Vlans on both stacks with the first stack Vlan 1 ip address 10.1.1.30 255.255.255.0, stack 2 with Vlan 1 ip address 10.1.1.31 255.255.255.0, set the ip default-gateway on switch stack 1 with 10.1.1.30 and on switch stack 2 with 10.1.1.31, and we are able to communicate to all Vlans on each stack.

My problem is when we add another network with a cisco 3560 switch on network 192.168.1.0 255.255.255.0, configured the FA0/43 port with trunking, and on the 3750 stack we configured trunking on gi1/0/48, then create the new interface Vlan 2 with ip address 192.168.1.247 255.255.255.0 in the same subnet as the 3560 switch. I have two console windows up as one for the 3750 stack and another for the 3560 and see the trunk ports come up and online along with the protocol online. I setup IP route 192.168.1.0 255.255.255.0 192.168.1.1 so all traffic for the 192.168.1 networks will go to the 3560 switch.

I then try pinging the 3560 from the 3750 stack with no response. I checked the cdp neighbors detail and see each other on Layer 2, but we can't ping from either 3560 or 3750 switches and both are on the same subnet.

I'm not sure why the Layer 3 works for the 10.1.1.0 network but fails to work on the 192.168.1.0 network

I need your help to figure this out.

Thank you

Everyone's tags (4)
10 REPLIES
Silver

connecting multiple networks with switches

Hi Pain,

So if we focus on the area where you have the ping problem, we have the illustration below. 

3750_Stack (Vlan2_192.168.1.247 /24)-Gi1/0/48   <----trunk--->   Fa0/43_3560 (Vlan2_192.168.1.1 /26).

I understand you have enabled ip routing on the 3750s (with "ip routing"), configured the static route (btw as the routing is enabled the default route should be defined with 'ip route 0.0.0.0 0.0.0.0 x.x.x.x), created the L3 interfaces, have validated the status of the trunk..

One question has the VLAN 2 been created in the vlan database (show vlan  [id 2]) ? Is this vlan allowed on the trunk ('show interface trunk) ?

Best regards.

Karim

New Member

connecting multiple networks with switches

I have thr trunks working from 3750 stack to 3560 switch - we created vlan 2 on 3750 with ip 192.168.1.247 ok but on the 3750 switch the Vlan is 1 with 192.168.1.1 - will this cause a problem?

Now on the new 3750 stack we did the IP route 192.168.1.0 /24 to 192.168.1.1 but we did not add route 0.0.0.0 0.0.0.0 to what interface or IP address should we use.

We did add the switchport trunk allowed vlan 1, 2

Thanks

Silver

connecting multiple networks with switches

Hello,

Is the vlan 2 (+ interface vlan 2= 192.168.1.1) created on the 3560 as well ?

I do not think "ip route 0.0.0.0 0.0.0.0 x.x.x.x" in global config mode on the 3750s is part of the problem, it was just a suggestion for the default . Moreover you have added a more specfic static route to 192.168.1.0 /24 towards the 3560..

Is 192.168.1.1 the ip @ of the vlan 2 on the 3560 ??

If it can help you also post the intersting configuration parts on both 3750 and 3560.

Best regards.

Karim

New Member

connecting multiple networks with switches

I the vlan for the 3560 is vlan 1 already on the switch when we began this project with 192.168.1.1 /24

I removed everything from the 3750 stack - confirmed trunk ports are online for 3750 stack / 3560 switch, created the interface vlan 2 with ip address 192.168.1.247 /24 - confirmed port in vlan 2 and see vlan online or up up - then create the ip route 192.168.1.1 255.255.255.0 192.168.1.1 and still not able to ping - still able to see the switches using cdp neighbors detail

Not sure what's going on

Thank you

Silver

connecting multiple networks with switches

Hello Pain,

Thanks for the feedback.

So I understand that :

- On the 3750 - int Vlan2 is on subnet 192.168.1.0 /24 / int vlan 1 is on subnet 10.1.1.0 /24

- On the 3560 - int vlan1 is on subnet 192.168.1.0/24

- There is a trunk allowing vlan 1 & 2 between them.

I think there is mismatch in the vlan/subnet definition that has been set up between 3560 and 3750..The configuraiton should be consistent between both switch.

So could you please test to change the adressing on the 3560.

On the 3560 Instead of =>

interface vlan 1

ip address 192.168.1.1 255.255.255.0

Please configure =>

interface vlan 1

no ip address

interface vlan 2

ip address 192.168.1.1 255.255.255.0

no shut

================================

Also I had to indicate this but on the 3750 you do not have to configure "ip route 192.168.1...." as this subnet is DIRECTLY CONNECTED...We are on the same subnet...

If it is not possible to change this on the 3560 then could you please try to put the 192.168 under the vlan 1 interface on the 3750.

Regards.

Karim

New Member

connecting multiple networks with switches

I will try this in the morning, thanks for your help

New Member

connecting multiple networks with switches

Hello,

I was able to complete the steps outlined in your posting but we still have the same issue - we can coonect the 3750 stacks  and able to ping the IP address on them. We are able to connect the 3750 stack to the 3560 switch with trunking only, not able to ping the 192.168.1.0 network from either the 3560 or 3750 stack - layer 3 not working on one network.

I will wipe the 3750 stack only as the 3560 is in production, then configure Vlan 1 with the 192.168.1.0 network verses the original configuration with the 10.1.1.0 network.

Question - can this be aNative vlan issue - as the 10.1.1.0 network works find on Vlan 1 - the 192.168.1.0 network is on Vlan 2 , the trunk port takes care of this as all trunk ports are in the Native Vlan right?

Thank you Sir

Silver

Re: connecting multiple networks with switches

Hello Pain,

Thanks for the feedback.

About your last question I do not think it is a native vlan mismatch between the two switches, because it would have caused a spanning-tree PVID inconsistency just like described on the second point of this chapter =>

http://www.cisco.com/en/US/tech/tk389/tk621/technologies_tech_note09186a00801d11a0.shtml#topic2

You can also check what is the native vlan on each side (3560 and 3750), with the command 'show interface trunk'.

By default, the Native vlan is 1 => So if you have not modified this value, the native is 1 between the 3750 and the 3560.

================You can check with the command ===================

Switch #show interfaces trunk 

Port             Mode             Encapsulation  Status        Native vlan

Gix/y(/z)         on               802.1q         trunking        1

......

and so on ..Be sure that the intersting vlans are allowed and active and not pruned on the trunk.

===================================

It is important to have a consistency between the created vlan (in the vlan database - L2) and the L3 associated address on each side of the trunk.

If you cannot change the vlan ip address on the production 3560, so yes you can try it on the 3750.

It should work as we would be directly connected through the vlans allowed on the trunk, in the same broadcast domain, with a consistent IP addressing on each side.

You can also test by plugging a PC on the 3560, put the 3560 interface in vlan 2, assign to the PC a static address in the 192.168.1.x/24 range and try to ping the 3750 on this range. It would confirm it is just an addressing problem.

Best regards!

Karim

New Member

connecting multiple networks with switches

Karim,

I wiped the 3750 stack we are adding to the network then configured Vlan on the 192.168.1.x network and same as the 3560.

I then created the trunk links for 3750 stack and connected to the 3560 and the links came up. I'm able to talk with the 192.168.1.x network, and not able to test the 10.1.1.x network as I located we have a bad gbic fiber module - I think this was causing our problem connecting the switches.

I can't thank you enough for all the time spent help me with this crazy problem, I really appreciate your help and hope the gbic module is the root cause for the issue.

Thank you my friend.

Silver

connecting multiple networks with switches

Hello,

You are very welcome my friend  !

Thank you for you kind feedback and the rating. Glad to be of some little help..

Feel free to ask if needed.

Best regards.

Karim

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