Cannot ping certain VLANs

[william.luzdossantos]

Hi all, this is my first time posting in the community. As a beginner, naturally, there are simple things that I still don't understand, I hope someone may help me. Please can you consider the following scenario:

- In my network, I have two main switches Catalyst 3750-X working as L3 routers, each one in different locations, routing the same VLANs (approximately 30). The thing is that although they're routing the same VLANs, the VLANs are routed having different IPs on each switch, something similar to this (the numbers are just examples):

	Switch 1 IP routing (IP xxx.xxx.0.1)	Switch 2 IP routing (IP xxx.xxx.0.2)
VLAN1	xxx.xxx.1.1	xxx.xxx.1.2
VLAN2	xxx.xxx.2.1	xxx.xxx.2.2
VLAN3	xxx.xxx.3.1	xxx.xxx.3.2
VLAN4	xxx.xxx.4.1	xxx.xxx.4.2
VLAN5	xxx.xxx.5.1	xxx.xxx.5.2
VLAN6	xxx.xxx.6.1	xxx.xxx.6.2
VLAN7	xxx.xxx.7.1	xxx.xxx.7.2
VLAN8	xxx.xxx.8.1	xxx.xxx.8.2

...and so on for all the other VLANs. The subnet mask is /24 to all VLAN.

Now, let's say that a device is on VLAN 2, for example, listening to the router 2, its gateway will be xxx.xxx.2.2 . Even though my PC's gateway is xxx.xxx.0.1 (router 1), I can ping the device without any problem. 

This works fine for most of my VLANs regardless the PCs or devices' gateways/VLANs. However, I'm trying to add some other VLANs to the system, following the pattern mentioned above, and, unless my PC is configured to same router as the device, I cannot ping it. In other words, the example that I mentioned above does not work. For my PC to see a device that is on VLAN 31, listening to router 1 (IP routing would be xxx.xxx.31.1), my PC's gateway must be configured to router 1 as well (xxx.xxx.0.1).

My question is, why I can connect to certain VLANs from my PC regardless of its gateway, but I can't connect to others? Is the configuration that I presented correct in the first place? I assume that as I can successfully do it with most of my VLANs, I should be able to do it with all the other that I create. 

Sounds a dumb question but I will appreciate any help as I am stuck with this small problem.

[Reza Sharifi]

Hi and welcome to the forum.

Your question is not dumb and valid. 

It maybe that you are running a routing protocol (OSPF, EIGRP, etc..) between the 2 routers or between switches and routers and the new vlans that are not working have not been added to your routing protocol. You can take a look at that or just post the output of "show run" from both core switches/routers here for us to look.

HTH

[william.luzdossantos]

Hi Reza, thanks for replying me.

The only routing protocol present in both core switches is the "Static" which is configured to their Gateway IPs. So, when I add new VLANs to the routers, should I reconfigure the routing protocol?

Thanks for your help, I really appreciate.

[Reza Sharifi]

Hi,

Ok, so you are using static routes and not dynamic routing protocol.  So, most likely you have a set of static routes configured in each core switch.  Now you need to add static routes for these new vlans you are creating so they are reachable from other devices and subnets.

something like this example:

ip route vlna31 subnet (10.10.10.0 255.255.255.0  x.x.x.1 or 2

HTH

[william.luzdossantos]

Hi Reza,

We finally found the problem here! One of our switches located between the two core ones was not tagging the problematic VLANs to the trunk port. Now we learnt the lesson to always double check the configuration of all the hardware once we get this sort of situation.

Thank you so much for your help, I am very appreciated!