Inter VLAN routing with OSPF

[Ninad Thakare]

Hi,

I face-off a scenario, where the inter VLAN routing is need to be done with OSPF on Cisco Layer 3 switch.

Can any one please elaborate how could that be done...?

Regards,

Ninad Thakare

+91-814-991-6196      

[Jon Marshall]

We need more details.

On a L3 switch doing inter vlan routing you do not need a routing protocol to route between the vlans because each L3 vlan interface/IP subnet is seen as directly connected to the L3 switch.

Do you mean run OPSF between the L3 switch and other L3 devices.

Please clarify.

Jon

[Ninad Thakare]

Hi,

Thanks for your reply.

I will elaborate you a architecture.

ISP -> Fortigate Firewall -> cisco 3850 -> cisco 2960.

On 3850, there are 4 vlans suppose, VLAN 2 - 10.0.0.0/24,

VLAN 3 - 20.0.0.0/24

VLAN 4 - 30.0.0.0/24

VLAN 5 - 40.0.0.0/24

There are few devices under vlan2 which requires Dynamic routing to communicate with other VLAN and only runs on OSPF, will this much of information will be OK to get you what I want.

Regards,

Ninad Thakare

[Jon Marshall]

Ninad

Still not sure i follow. If the devices in vlan 2 need to communicate with other vlans on the same switch then if all the vlans are on the same switch you do not need to run OSPF.

As long as -

1) you have an SVI for each vlan with an IP address (SVI = "interface vlan " in your config

and

2) you have enabled ip routing

then the switch will route between the vlans without a routing protocol because they are directly connected routes ie. do a "sh ip route" on the switch and you should see an entry for each vlan.

Are you talking about running OSPF between the 3850 and the firewall ?

Jon

[Richard Burts · Accepted solution]

I am reading the post from Ninad Thakare and focusing on the part where he says "There are few devices under vlan2 which requires Dynamic routing to communicate with other VLAN and only runs on OSPF". Am I correct in understanding that you want to run OSPF on the layer 3 switch so that some devices connected in VLAN 2 will participate in OSPF and learn the other subnets that are available? If so it should be a fairly simple setup. On the layer 3 switch configure an OSPF process and configure network statements to include each of the subnets. I would think that this would do what you need. If I have not correctly understood what you need then please provide clarification.

HTH

Rick

[Ninad Thakare]

Yes Richard,

You are right. I need the same.

I too thought of configuring OSPF with advertising all VLAN's in area 0.

But was not sure, whether it will work and fulfil my need or not..?

Brgds,

Ninad

[ashirkar]

Hi Ninad,

Are you running OSPF between fortigate and cisco 3850 ?

As per your given network diagram flow, i can see your all host connected to cisco 2960( in different VLANs) and your 3850 is having SVI (you have configure with int vlan command for each VLAN).

Let us what protocol you are running between FW and 3850 and FW to ISP .Please provide more information and detail about your problem to community users so we can help you.

Regards,

Ashish

[Inderjeet Singh]

Richard,

There is alreday Inter VLAN routing enalbed on 3850.. so why OSPF is required to learn subnets which are on the same switch ??

[Richard Burts]

It is my understanding that there are hosts in the VLAN that need to run OSPF and use OSPF updates to learn the network topology. I believe that  Ninad confirms that this is correct. In that case the intervlan routing on the 3850 is not sufficient.

Ninad

You ask whether configuring an OSPF process and configuring network statements for each subnet will work. I see no reason, based on what you have told us so far, that it would not work. You also ask whether it will fulfill your needs. Since we do not have a clear understanding of what these needs are we can not really answer that part of the question.

HTH

Rick

[Ninad Thakare]

Thanks every one,

Its done.

I just advertise all my VLAN subnets under area 0. And its working fine.

Brdgs,

Ninad

[Richard Burts]

Ninad

I am glad to know that it is working fine. Thank you for posting back to the forum to let us know that following our suggestions did lead to a successful implementation. Now that it is done and working perhaps you could mark the question as answered?

HTH

Rick