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New Member

Subinterfaces

Hi,

I configured 2 subinterfaces on a FE port on a router.

Here is what I configured.

int fa0/0

no ip address

int fa0/0.1

encapsulation dot1q 1 native

ip address 172.16.1.1 255.255.0.0

int fa0/0.2

encapsulation dot1q 2

ip address 192.168.1.1 255.255.0.0

I noticed I can only ping from int fa0/0.1 but not fa0/0.2 to directly connected interfaces of another router.

I suspect I can ping from fa0/0.1 because it is a native vlan.

Can some1 advice me what steps I have missed out?

What should I do to ping from fa0/0.2?

thank you!

7 REPLIES

Re: Subinterfaces

Could you please paste a N/W topology. Please paste config of the routers also. I believe that you have a switch connmected to the above router and a trunk is setup on that with vlan 1 and Vlan 2 defined on the switch.Your anotheer router has to be on vlan 2 and make sure about it. Also make sure about the physical connectivity.

What does " show int fa 0/0.2 " shows you.

Please revert.

regards,

-amit singh

New Member

Re: Subinterfaces

oops! i 4got abt the switch! hee hee!

:P

so .... let's confirm

i have to configure a port on the switch to become trunk to carry the vlans 1 and 2 of the router port

what do you mean by "your another router has to be on vlan 2"?

My destination router is a pure router without any subinterfaces or vlans configured.

So, do I have to configure this destination router to have vlans?

How?

Pls advice quickly.

thank you.

Purple

Re: Subinterfaces

That is basically correct on your switch that you have connected to your router set up your link as a trunk , transparent mode and make sure you allow vlans 1 and 2 across the link , all vlans are alowed by default so unless you manually prune off the others you should be ok . also make sure you create the layer 2 vlans on the switch. Also make sure on the link from the switch to the router that your encapsulation matches whats on the router.

Re: Subinterfaces

You wrote " So, do I have to configure this destination router to have vlans? "....

No what you have to make sure is that the device that you are connecting to the switch lies in the same subnet as on the same vlan as the IP defined on the router. for example.

int fa0/0.1

encapsulation dot1q 1 native

ip address 172.16.1.1 255.255.0.0

int fa0/0.2

encapsulation dot1q 2

ip address 192.168.1.1 255.255.0.0

If your another router has an IP 192.168.1.10 255.255.0.0, so it will be on vlan 2 on the switch. If any other device has an IP 172.16.1.x / 16, so it will be on vlan 1 on the switch.

HTH,

-amit singh

New Member

Re: Subinterfaces

Hi Amit and Grant,

I a bit confused here.

So, I want to connect routerA with sub-interfaces to routerB and routerC w/o subinterfaces.

Q1) For the switch port connecting to routerA, I configure it has trunk allowing vlan 1 (172.16.x.x) and vlan2 (192.168.x.x). Right?

Q2) For the switch port connecting to routerB and routerC, what should I configure?

Should it be access or trunk?

Q3) I do not need to specifically configure vlan on routerB and routerC, right?

Q4) I have configured the switch as "vtp mode transparent". Right?

Q5) For the switch, do I make the trunk port as "nonegotiate"?

I still cannot ping from routerA to routerB nor from rotuerA to routerC.

Pls advice

Thank you

Silver

Re: Subinterfaces

1) Pt 1 is right

2) The port will be an access port.

3) Nopes you can do on the native etherne interface

4) Yes correct again if it is a standalone switch

5) It should not be an issue

HTH

Re: Subinterfaces

Hi,

All the questions have been answered in last post.

The link from switch to router B and C will be asn access port as you router A is already configured for inter-vlan routing and there is not need to trunk on other routers.

Now, Please let me know the IP addresses on the router B and router C's interfaces connecting on the switch. As I mentioned in my earlier port that if the router has an interface Ip as 172.16.x.x segment it will be an access port on Vlan 1 and 192.168.x.x. so it will be an access port on valn 2 on the switch.

Now if you are pinging from router B to C if they are in different sengment you need a reverse route or defalt route on each router to send the traffic back. For example on router B just put.

conf t

ip route 0.0.0.0 0.0.0.0

On router C,

conf t

ip route 0.0.0.0 0.0.0.0

regards

-amit singh

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