Inter-Vlan routing, routing protocol needed?

[vipinrajrc]

Hi Experts,

I have one doubt. For inter vlan routing only layer3-vlan is required, right? or any routing protocol needed?

We have 20 access-layer switch wich are in different vlans. Layer3-vlans are created in core switches for the corresponding layer2 vlans.

Do i need to enable ospf for inter-vlan routing? or only layer3 vlan interface is required?

Thanks

Vipin

[Jon Marshall]

Vipin

If all the L3 vlans are on the core switches then technically no you do not need to run a routing protocol assuming you are running something like HSRP for the vlan interfaces because they all are directly connected routes.

If however you have other L3 devices connected to the core switches that need to know these routes then you can use statics or more likely you can use a dynamic routing protocol such EIGRP/OSPF.

Jon

[vipinrajrc]

Hi,

We are running HSRP for each interface.We are taking control of the infrastrucutre now, before that some other company was managing that infra. While we have checked it OSPF is running. So i have a doubt like this.

In this infra all the switches have connection to each other. So no need to OSPF or any other routing protocol is not required?

Shall i remove OSPF?

Thanks

Vipin

[Jon Marshall]

Vipin

If you are running HSRP and the interconnect between the L3 switches is a L2 trunk then no you don't need OSPF but then again it doesn't do any harm to run it. You should  do a "sh ip ospf neighbors" to determine exactly what, if any, these core switches are peering with.

Only turn OSPF off if -

1) you really have a good reason to

and

2) you are absolutely sure it is not needed.

There many not be a need for it but usually if a device is running something there is a good reason for it.

Jon

[Joseph W. Doherty]

Disclaimer

The    Author of this posting offers the information contained within this    posting without consideration and with the reader's understanding that    there's no implied or expressed suitability or fitness for any   purpose.   Information provided is for informational purposes only and   should not  be construed as rendering professional advice of any kind.    Usage of  this posting's information is solely at reader's own risk.

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In    no event shall Author be liable for any damages whatsoever  (including,   without limitation, damages for loss of use, data or  profit) arising  out  of the use or inability to use the posting's  information even if  Author  has been advised of the possibility of such  damage.

Posting

If there's only a single L3 core device, it will route between VLANs (which have defined interfaces in the VLANs) as they would all be "connected".

You only need a routing protocol or static routing statements if other networks are beyond another L3 device.

[Jon Marshall]

Joseph

Firstly, good to see you back after quite a while. Meant to say hello when i first spotted you posting again but i have been an intermittent user recently. Glad to have you back as your knowledge has been sorely missed, certainly by me when it comes to QOS for example.

Anyway to the point -

If there's only a single L3 core device, it will route between VLANs (which have defined interfaces in the VLANs) as they would all be "connected".

I thought about this too but even if there are 2 cores interconnected via a L2 trunk i still can't see the need for a routing protocol, assuming you are running a FHRP such as HSRP.

Jon

[Joseph W. Doherty]

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

Jon, thanks so much for your kind remarks!

I stopped posting when Cisco revised this site and we had to agree to the updated Acceptable Use Agreement.  I wasn't too keen on provision #11, Indemnity.  Asked Dan about it, but seems to have been beyond his control.  Started posting again when I came up with the above legalese.

In any case, you're quite correct, you're not limited to a single device.  What you posit would also work for N devices.  The key point, which I think you'll agree, is my second statement "You only need a routing protocol or static routing statements if other networks are beyond another L3 device."

[Jon Marshall]

Joseph

I did wonder about the disclaimers, perhaps i had better reread the Acceptable Use agreement.

Yes i would agree with last statement completely.

Jon

[Sonugnair_2]

Hi Vipin,

Chech for the output of "show ip ospf nei". If it is populated it means that you have OSPF in production. In this case check "show ip route ospf". If you see any O routes it means remote networks are being learned by your core switches. If above is true so not remove any configurations.