Stack

[Mohamad AMmar]

I have 5 cisco switches2 of them are configured as core stack and the others are connected to this stack. I configured vlans on the stack but when i try to connect devices to the edge i only receive vlan1 default.

[sidshas03]

Hello sir,

If you don’t see your custom VLANs listed there, it means those VLANs don’t exist on the edge switches. Remember, just because you created them on the core stack doesn’t mean they automatically appear on the others unless you're using VTP.

If you want the VLANs to sync automatically, you can use VTP (VLAN Trunking Protocol). But be careful, if not set up properly, VTP can wipe out your VLANs. Here’s the safe way to do it:

On core switch (set as server):

conf t
vtp mode server
vtp domain mydomain
vtp password mypassword
end

On edge switches (set as client):

conf t
vtp mode client
vtp domain mydomain
vtp password mypassword
end

Make sure all switches are in same domain and using same password.

Also, check if the interfaces where you are connecting edge devices are assigned to proper VLANs. Use this command:

conf t
interface <interface-name>
switchport mode access
switchport access vlan <vlan-id>
end

This way, device will go to correct VLAN, not just VLAN1. 

[Mohamad AMmar]

I noted that all switches have same vlan, so not just core also edge . But i see that i have 2 units field ! I should config unite 2 like 1 or its automaticaly?

[sidshas03]

Hello sir,

Yes, if you are seeing two units showing differently in the stack, it may be possible that unit 2 is not fully in sync with unit 1. Even though VLANs are same on all switches, sometimes the configuration doesn’t apply properly to all units in the stack.

Best way is to check if unit 2 is properly joined in the stack and has same config like unit 1. You can use show switch command to confirm stack membership and roles. If needed, you can manually configure unit 2 same as unit 1, or copy the config using TFTP or console access.

Also confirm that interface ports on unit 2 are assigned to correct VLAN using:

conf t  
interface <interface-name>  
switchport mode access  
switchport access vlan <vlan-id>  
end  

Sometimes stack sync issues happen due to version mismatch or bad stacking cable also, so just double check that as well.
Hope this helps!

[Joseph W. Doherty]

A tad more info would be used, like representative examples of core and edge switch configs.

[Mohamad AMmar]

My main question for now is: stack meaning that 2 core switshes have same configurations ? Or just database vlans are same and physical ports need to set on 2 units manually!?

[sidshas03]

Yes - in a stack, both core switches share the same configuration and VLAN database, but physical ports must be configured manually per unit.

Explaination:

In a Cisco switch stack, the two core switches operate as one logical switch with a single, unified configuration file. This means the VLAN database is automatically shared between both units when you create or modify a VLAN, it applies to the entire stack. However, physical port configurations are not applied globally. Each port must be configured individually based on its unit and port number. So while VLANs are common across the stack, you still need to manually configure physical interfaces (e.g., access/trunk mode, VLAN assignments) on each unit. For example, a port on unit 1 is referenced as Gig1/0/x, and a port on unit 2 as Gig2/0/x, and both need to be configured separately even though they are part of the same stack.

[Joseph W. Doherty]

From a configuration standpoint, a "stack" is configured very much like a chassis, where each stack unit's ports are configured like a chassis unit's line card ports.