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Highlighted
Explorer

ISR 2921 sub-interface

Hi,

I want to connect 2 ISP links into one  Gigabit-interface on my Router 2921, can any one tell me how to do that ?    sub-interface creation is not possible on cisco 2921

plz help me

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2 ACCEPTED SOLUTIONS

Accepted Solutions
Highlighted
Rising star

ISR 2921 sub-interface

Hi Imran,

I didn't realize that the switch doesn't even have a login option :-( So it would be more of like a HUB then. It worth checking (google it) if your switch model understand 802.1q tagged frames.More likely they wouldn't be. In that case you will have go with a manageable switch. Also it worth trying to have your router configured with sub interface and connecting the port to your unmanageable switch and see if you are able to ping your service providers router.

As updated before another option you could try is secondary ip address but again that is not a scalable option and i wouldn't recommend the same for a long run.

Regards

Najaf

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VIP Mentor

ISR 2921 sub-interface

No i can not connect 2-isps into 2 gi0/1 and gi0/0,  because that is used for other purposes.  we have only one Gigiabit-int availble that has to be connected into 2-isps .

Then you have to use a different switch or a module in the router. I would go for the module as there will be one device less to manage.

-- 
Don't stop after you've improved your network! Improve the world by lending money to the working poor:
http://www.kiva.org/invitedby/karsteni

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11 REPLIES 11
Highlighted
Rising star

ISR 2921 sub-interface

Hi Imran,

Are you sure that sub-interface creation is not possible in 2921?

Also if you have 2 ISP links I would assume there would be two physical cables coming from these ISP's as well. Is that not the case????

Not sure if secondary ip address on the interface will do the job for you as below even though it is not a good practice.

interface FastEthernet0/0

ip address 192.168.10.10 255.255.255.0 secondary

ip address 10.10.10.10 255.255.255.0

shutdown

Regards

Najaf

CCIE (R&S) 25070

Highlighted
VIP Mentor

Re: ISR 2921 sub-interface

Subinterfaces can also be configured on a 2921. Here is an example:

interface GigabitEthernet0/1

  no ip address

  duplex auto

  speed auto

!

interface GigabitEthernet0/1.16

  encapsulation dot1Q 116

  ip address 172.16.1.1 255.255.255.0

  ...

!

interface GigabitEthernet0/1.10

  encapsulation dot1Q 10

  ip address 10.10.10.1 255.255.255.0

  ...

-- 
Don't stop after you've improved your network! Improve the world by lending money to the working poor:
http://www.kiva.org/invitedby/karsteni

Highlighted
Explorer

ISR 2921 sub-interface

Thanks Karsten,  yes after your example, it is possible to configure sub-interfaces on 2921. because i didnt know that

can you tell me after adding those 2-sub-interfaces into  2-vlans (116 & 10) ,   then the Router interface GigabitEthernet0/1  should be physically connected into a switch which must be a managable switch ? and should configure that switch port as TRUNK LINK for vlans (116&10) ?

im asking the question, because i dont have cisco switch in between my 2-ISPs and my Router,    that is a normal D-Link switch  (Un-Managable Switch)

Please tell me what is the solution ?   my d-link switch is not configurable, it is plug&play

Highlighted
Rising star

ISR 2921 sub-interface

Hi Imran,

You dont need a managable switch. You can use a un managable switch and put two ISP's in different VLAN (116 & 10) and configure the switch port as trunk which is getting connected to yout 2921 router.

Hopet his helps

Regards

Najaf

CCIE (R&S) 25070

Highlighted
Explorer

ISR 2921 sub-interface

Hi Najaf,

But how to configure un-managable switch-port as Trunk ?  

Highlighted
VIP Mentor

ISR 2921 sub-interface

Yes, you need a managed switch in that case. The Port to the router has to be a trunk port and the two ports to the ISP-routers have to be in their VLANs as an access-port. A cheap SG300-8 would do that job.

Two other ways to solve that:

1) Use gig 0/0 and gig 0/1 for your ISPs and gig 0/2 for your internal connection. There you probably have a managed switch if you need more logical interfaces.

2) Use a switch module that you install in one of the slots and configure vlans for the ISPs there:

http://www.cisco.com/en/US/products/ps10537/products_relevant_interfaces_and_modules.html#esm

-- 
Don't stop after you've improved your network! Improve the world by lending money to the working poor:
http://www.kiva.org/invitedby/karsteni

Highlighted
Explorer

ISR 2921 sub-interface

No i can not connect 2-isps into 2 gi0/1 and gi0/0,  because that is used for other purposes.  we have only one Gigiabit-int availble that has to be connected into 2-isps .  

Najaf ,  you suggested me to configure the Un-Manageble switch-port as Trunk.  but how to do that,  un-managable switch means that isnot configurable .  i can not login or enter to that d-link siwtch

Highlighted
Rising star

ISR 2921 sub-interface

Hi Imran,

I didn't realize that the switch doesn't even have a login option :-( So it would be more of like a HUB then. It worth checking (google it) if your switch model understand 802.1q tagged frames.More likely they wouldn't be. In that case you will have go with a manageable switch. Also it worth trying to have your router configured with sub interface and connecting the port to your unmanageable switch and see if you are able to ping your service providers router.

As updated before another option you could try is secondary ip address but again that is not a scalable option and i wouldn't recommend the same for a long run.

Regards

Najaf

View solution in original post

Highlighted
Beginner

ISR 2921 sub-interface


Hi Imran,

Najaf is correct please consider him, in this scenario you should need layer 3 switch or Manageble swtich to got the subinterfaces with trunking between the different Local VLANS.

Thanks to  Imran

Regards

Naresh

Highlighted
VIP Mentor

ISR 2921 sub-interface

No i can not connect 2-isps into 2 gi0/1 and gi0/0,  because that is used for other purposes.  we have only one Gigiabit-int availble that has to be connected into 2-isps .

Then you have to use a different switch or a module in the router. I would go for the module as there will be one device less to manage.

-- 
Don't stop after you've improved your network! Improve the world by lending money to the working poor:
http://www.kiva.org/invitedby/karsteni

View solution in original post

Highlighted
Explorer

ISR 2921 sub-interface

Thank you all for your support. i will go for manageable switch ,  i think i will go with Kareten suggeted cheap switch  SG300-8

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