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New Member

About the connection of two Catalyst

Dear Sirs,

How is the port configuration when two Catalyst is connected?

Two Catalyst becomes the same segment.

bridge? or trunk?

Best regards,


Re: About the connection of two Catalyst

There are two port configurations - trunk and access. Access means the port belongs to a single vlan. trunk port means traffic to and from configured vlans on the switch will can propagate through that trunk port. Ports that are in the same vlan are virtually bridged, meaning broadcast traffic from pc in vlan 1 will be heard by all the PCs in the same vlan but not by the PCs in vlan 2 or any other vlan.

New Member

Re: About the connection of two Catalyst

Thank you for the reply.

It extends in two Catalyst though it is same VLAN.

In that case, it is a "trunk port" ?


Re: About the connection of two Catalyst

If the ports in question are configured with the command "switchport mode trunk" then they are trunk ports & if configured with "switchport mode access" they are members of a VLAN and do not participate in trunking.

To check if the port in question is in trunking mode or if it belongs to a particular vlan and is in access mode, use the command "show port module/port"


Re: About the connection of two Catalyst

Both access and trunk port can extend the vlan in both switch (extend means the broadcast domain for that vlan is extended to the other switch). The trunk port simly means that vlans can propagate through that port while access port only allows traffic for the vlan the access port belongs.

I think the main thing is understanding what a vlans is - it is simply a broadcast domain. Think of a vlan as being in the same subnet. In a switch there is a virtual bridge where all the ports that belongs to the same vlans are "bridged" internally. A port belonging to a single vlan is an access port. A trunk is simply a way to connect switches together without using a single port for every vlan. for example, you have ten vlans in your network and you have two switches. you want these same vlans in one switch to extend to another switch. without a trunk you will have to connected ten different "access" port so that these vlans can talk to the other device in that same vlan at the other switch. With a trunk you need only one port and have the same ten vlans go through that same port. Point is "access" port belongs to one vlan - trunk allows propagation of multiple vlan and that single port.

New Member

Re: About the connection of two Catalyst

> bosalaza

Thank you for a detailed explanation.

With two switches for same VLAN, Is it "access port" or "trunk port" ?

New Member

Re: About the connection of two Catalyst

If both switches are in same VLAN swicth port acess if fine

New Member

Re: About the connection of two Catalyst

It is thanks.

Please teach a little more in detail.

Is there a different point in "access port" and "trunk port" for this case?

For instance, "Broadcast" extends.

New Member

Re: About the connection of two Catalyst

well you can use the following configuration

interface gigabitethernet 0/1

switch port

switch port mode trunk

switch port trunk encapsulation dot1q

no shut