ARP request

[uosambela]

Hi,

i would like to know if there's a way  to transmit the arp request to the same interface that is generating it.

I mean: how can I forward the arp request to the interface that is generating it?

Some of you will find it very weird but I have a gpon deployment attached to a unique physical port on an catalyst 3750. So, i have to recieve the arp requests on the port where i generate it.

I don't know if it's clear enough.

sorry for my english.

thanks

[aftabsiddiqui]

Yes, you are right, it is not clear at all. Best solution would be to make a diagram and share it along with the use case. 

[uosambela]

Hi to all.

Here's attached a simple schema to show what i want.

We got two ONTs with a couple of computers attached on each one, PC-1 and PC-2.

We want to access from PC-1 to PC-2.

When we try to ping the request travels from Ont to Smart OLT and finishes in the 3750. So when the request arrives to Cisco port it sends it to all the ports except to the one that came from. In this case the gi1/0/1.

What I need is to send back that request to Gi1/0/1, the same port that originated this request.

Hope this clears the problem.

I'm really sorry for my English.

thanks for all.

[Shaunak]

Hello,

Can you also tell us about the layer 3 boundaries in the network?

When you ping from the ONT to the in line smart OLT the ARP request should be ingress on the Pon1 interface, does the Smart OLT intercept this and respond back or will it only respond to the requests coming in on the interface connected to the switch?

What is the default gateway of the ONT devices? I'm assuming that all of the devices are in the same subnet.

Thanks,

Shaunak

[uosambela]

Hi Shaunak,

thanks for the reply.

The smartolt intercepts the traffic on Pon1 interface. the smart OLT has a GE interface that you connect it to the Cisco switch. Let's say that this interface corresponds to Pon1 interface.

So according this the traffic flow is as follows on the attached image.

sorry for my english

thanks for all

[Shaunak]

Thank you for the prompt response.

It seems that PC1 or ONT-1 is trying to reach PC-2 behind ONT-2, am I right?

I don't think so that this will be feasible until and unless you have multiple L2 interfaces going to the Smart OLT. Also, subjected to how it handles STP, since if it forwards STP BPDUs then the additional link will also get blocked.

Your design is going against how the IOS is programmed or how it behaves when it comes to conventional networks, since it's expected that if there was an ARP request on that interface the destination is inherently not connected to the interface and even if it is then the underlying infra will get the ARP request to the dest device and back e.g. you have a hub connected to the switch then the switch will not forward that ARP request back on that interface and keep flooding that request again and again since the ARP process will be initiated by an end host or any L3 enabled device but a L2 switch which has only VLANs configured will not initiate the request. 

The switch will only initiate an ARP request if it has a corresponding SVI and needs to communicate with the device.

This design would not be supported in my opinion.

Thanks,

Shaunak

[Rajesh Hirani]

Have you looked into source specific multicast documentation?

You should be able to covert the multicast into uni cast and send it back to a single host ?

[Shaunak]

Hi Rajesh,

I might be missing something here, how is SSM connected to an ARP broadcast.

Is there something that I can read up on or a specific sub-portion of SSM, if you can point that out will be helpful to all.

Thanks,

Shaunak

[Rajesh Hirani]

My solution is not going to work for only ARP. However, should accomplished what we are trying to do here. One link which I randomly searched on google:

http://lostintransit.se/2012/06/04/source-specific-multicast-ssm-and-igmp-filtering/

[Shaunak]

Rajesh,

I guess we're not on the same page here. SSM is not used to convert mcast into unicast. SSM is used to join a specific mcast group from a specific source or deny a source etc.

ARP requests would be broadcast in nature and not multicast. The link that you posted only shows how to enable SSM mcast and how to filter IGMP requests from the hosts.

Thanks,

Shaunak