router on a stick - intervlan

What kind of a router is it?  Model, etc.

What does "VLAN" really mean?  I think it means: electronic/software defined copper wires ... as distinct from a subnet such as 10.0.10.0 10.0.20.0 10.0.30.0, etc.

So, if all the LAN ports are grouped like a commodity router would do, then the ports look like a switch and all the ports are on the "same copper" if you will.
To have an *additional* LAN or VLAN then at least one of the ports has to be disconnected from the others.

So, for starters I'd say that there really is no default VLAN on a router.  There are just the ports and how they are connected internally.  But, if you want to call that LAN a VLAN, you may if you wish.

Perhaps the question derives from methods for VLAN tagging?  I'm not sure because the description here needs a bit of expansion.

Router do not have default VLAN, because it is a layer 3 device. It deals with IP, VLAN is a layer 2 thing

not true.  You can configure vlan on a router. That's what it is called router on a stick (making your router acts as a layer 3 switch). As a matter of fact, I just discovered that vlan1 is the default vlan on the router.

1841Router#sh vlans
 
Virtual LAN ID:  1 (IEEE 802.1Q Encapsulation)
 
   vLAN Trunk Interface:   FastEthernet0/0
 
This is configured as native Vlan for the following interface(s) :
FastEthernet0/0
 
   Protocols Configured:   Address:              Received:        Transmitted:
           IP              192.168.1.250        112698817           100300750
        Other                                           0             4316955
 
   114119817 packets, 86815819169 bytes input
   104617705 packets, 25894622847 bytes output
 
Virtual LAN ID:  10 (IEEE 802.1Q Encapsulation)
 
   vLAN Trunk Interface:   FastEthernet0/0.10
 
   Protocols Configured:   Address:              Received:        Transmitted:
           IP              192.168.10.1           3289152             5300640
        Other                                           0               25255
 
   3289152 packets, 1844160049 bytes input
   5325895 packets, 6434062930 bytes output
 
Virtual LAN ID:  20 (IEEE 802.1Q Encapsulation)
 
   vLAN Trunk Interface:   FastEthernet0/0.20
 
  Protocols Configured:   Address:              Received:        Transmitted:
           IP              192.168.20.1          80089788            88293869
        Other                                           0              400201
 
   80089788 packets, 21576507314 bytes input
   88694070 packets, 75990106155 bytes output
 
Virtual LAN ID:  30 (IEEE 802.1Q Encapsulation)
 
   vLAN Trunk Interface:   FastEthernet0/0.30
 
   Protocols Configured:   Address:              Received:        Transmitted:
           IP              192.168.30.1           4708866             4467782
        Other                                           0               37730
 
   4708866 packets, 1439338993 bytes input
   4505512 packets, 2974238866 bytes output

Hi,

This depends on the router. If you're using sub interfaces then there is no default, you have to specify the vlan with the encapsulation sub interface command.

Some of the Cisco routers have built in mini switches and the configuration of these is the same as a layer 3 switch, in which case the default vlan is 1 if the port is an access port.

I am confused. I did not configure vlan1 on my router and how do you explain the output below:
1841Router#sh vlans
 
Virtual LAN ID:  1 (IEEE 802.1Q Encapsulation)
 
   vLAN Trunk Interface:   FastEthernet0/0
 
This is configured as native Vlan for the following interface(s) :
FastEthernet0/0
 
   Protocols Configured:   Address:              Received:        Transmitted:
           IP              192.168.1.250        112698817           100300750
        Other                                           0             4316955
 
   114119817 packets, 86815819169 bytes input
   104617705 packets, 25894622847 bytes output
...

Hi,

So your router IP configuration is:

FastEthernet0/0
 ip address 192.168.1.250 255.255.255.0

interface  FastEthernet0/0.10
 encapsulation dot1q 10
 ip address 192.168.10.1 255.255.255.0
 
interface FastEthernet0/0.20
 encapsulation dot1q 20
 ip address 192.168.20.1 255.255.255.0

interface FastEthernet0/0.30
 encapsulation dot1q 30
 ip address 192.168.30.1 255.255.255.0

The address 192.168.1.250 you have configured under interface FastEthernet0/0 (the physical interface) is by default in VLAN 1.

The physical interface FastEthernet0/0 is also the native VLAN. You can of course specify a different native VLAN by using the native keyword on the encapsulation sub interface command.

Yes agree.
Correct me if I'm wrong. But I think the default vlan is the native vlan.