question about router phusical interface tagging

Dr.X · ‎01-12-2013

hi , i want to ask a question about the topology above ,

as we see , we have two subinterfaces for two vlans

but my question is about the physical interface of router .

if i configured an ip on it ,

Question 1

how the switch will deal with it ??

i mean does the switch will tag this traffic from the physical interface ??

for any vlan it belongs to ?

Qutestion 2

as i configured router interfacs with encapsulation dot1q x

does that mean that the encapsulation or taggin is done inside the router before it go out of the subinterface ??

regards

mahmoodmkl · ‎01-12-2013

Hi
the switch will not tag if the ip is configured on physical interface and the switch config is access not trunk

the frames are tagged when they leave the trunk interface and the router can undersrand them

Sent from Cisco Technical Support iPhone App

Dr.X · ‎01-12-2013

so , wt will happen when i configure router physical interface an ip , and the switch was trunk.

to any vlan will be the traffic of the physical interface ???

i have confusion in this point !

Reza Sharifi · ‎01-12-2013

Yes, you can have IP address on the sub-interface and also physical interface of the router.

have a look at these 2 routers.

R1

R1(config-if)#do sh run int gi0/0

Building configuration...

Current configuration : 98 bytes

!

interface GigabitEthernet0/0

ip address 51.51.51.2 255.255.255.0

duplex auto

speed auto

end

R1(config-if)#do sh run int gi0/0.1

Building configuration...

Current configuration : 125 bytes

!

interface GigabitEthernet0/0.1

encapsulation dot1Q 50

ip address 50.50.50.2 255.255.255.0

no snmp trap link-status

end

R1(config-if)#

R2

R2#sh run int gi0/1

Building configuration...

Current configuration : 98 bytes

!

interface GigabitEthernet0/1

ip address 51.51.51.1 255.255.255.0

duplex auto

speed auto

end

R2#sh run int gi0/1.1

Building configuration...

Current configuration : 125 bytes

!

interface GigabitEthernet0/1.1

encapsulation dot1Q 50

ip address 50.50.50.1 255.255.255.0

no snmp trap link-status

end

R2#

I can ping fron r2 to r1

R2#ping 51.51.51.2

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 51.51.51.2, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/4 ms

R2#ping 50.50.50.2

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 50.50.50.2, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/1 ms

R2#

HTH

Dr.X · ‎01-12-2013

hi ,

thanks alot ,

but my problem is , for any vlan will the physical interface belongs to ??

assume i confiured the swutch port as trunk port .

regards

Reza Sharifi · ‎01-12-2013

Ok, lets clear a couple of things. Switches are not capable of doing sub-interfaces except for the 6500 series. Sub-interfaces are configured on routers and the example I provided you is from 2 Cisco 2800 routers.

In this above case the sub-interface is in vlan 50 and the physical interface is not in any vlan.

does this answer your questions?

If not tell me exactly what device you are talking about and is that device a router or a switch and what type?

HTH

Dr.X · ‎01-12-2013

hi , u r close to my answer ,

if the interface dont belong to any vlan , can we use it ????

how it will see the others in the connected to the switch ?

i mean how the traffic that dont belog to any vlanis carried by the switch ???????????????

about topology , assume i have a router on the right , and switch L2 on the left , thats it

regards

Reza Sharifi · ‎01-12-2013

if the interface dont belong to any vlan , can we use it ????

Yes you can, if it is switch, it will be a routed interface (without the switchport command) with just ip address

If it is router, then routers by default have just routed interfaces and if you configure a sub-interface you have to use dot1q encapsulation just like the above example I provided.

how it will see the others in the connected to the switch ?

about topology , assume i have a router on the right , and switch L2 on the left , thats it

Ok for you topology above the router is connected to the switch via 2 links. You can just keep the switch as layer-2 and trunk the ports to the router and put the ips on the routes for each interface or you can use the switch as layer-3 and have a routed connection between the two with ip on each side, In this case the switch needs to be capable of doing L3.

In the above scenario, it appears that 2 interfaces are in an etherchannel with ips on the router and the switch just layer-2

HTH

Raju Sekharan · ‎01-12-2013

Hi

if you have an IP address on the physical interface of the router and it is connected to a trunk port of a switch, the router physical interface IP can communicate to the native VLAN of that trunk

Thanks

Raju