Devices with no default gateway in a multilayer switch campus

[Habib Zakaria]

Hello

I have a campus size network with C6509 as a layer 3 switch and all the access switches are layer 2 switches. I have defined all the SVIs and VLANs in both the Core and access switches. I have noticed that end devices that have default gateway pointing the their SVI are pingable from the core, access switches and from other devices in other subnets. But the devices that have no default gateway those ones are only pinging from the core and I see the it in the IP ROUTE Table. but other switches or end devices can not reach those devices with no default gateway.

I think I have about 5 end devices that dont have gateway. Is there any solution for this problem generally without touching these end devices. Please note some of these devices are installed by contractors from vendors and are mainly HVAC, or monitoring devices and IT can not touch them.

Any solution will be highly appreciated.The model of the access switches are C3750s.

Regards,

[Jon Marshall · Accepted solution]

It depends on the end device.

Without a gateway set some end devices simply send an arp for all IPs whether they are on the same IP subnet or not.

If they do then you may be able to get connectivity working between vlans with proxy arp but it should be enabled anyway unless you have turned it off.

If it is enabled and it still doesn't work then you are going to have set a default gateway i'm afraid.

On the 6500 for the vlan that the clients are in can you do a -

"sh ip int vlan <x>"  

and see if proxy arp is enabled or not.

Jon

[Habib Zakaria]

Hi Jon,

Yes on the 6500 i did sh ip int vlan x and I do see the line showing proxy arp is enabled.

[Jon Marshall · Accepted solution]

I suspected it would be.

Then it looks like the devices are not sending an arp request otherwise the 6500 would respond on behalf of clients on different subnets and communication would work.

Unless there is something else blocking the communication eg. a firewall on the devices then it doesn't look like there is anything you can do without a default gateway set.

If you only need connectivity to these devices from an few IPs you could put them in the same vlan if possible but I can't think of anything else at the moment.

Jon

[Habib Zakaria]

I have asked these contractors to check the terminal network configuration and put the gateway. As of now The 6509 can ping the device but other access switches can not ping it and the clients in other subnets will not ping it.

Thank you for re-assuring the concept of Proxy ARP.