Duplicate Subnets on the Router and Firewall.

[xZamalek]

Hi Dears,

I was troubleshooting a connectivity issue for a host and observed that the gateway for the vlan is configured on The router as a sub interface and all switches are layer 2  , the same gateway is configured on the firewall , now when the router interface was shut no shut the connectivity was restored , how can duplicate subnet be an issue here ? I thought it might be because the arp request would get reply from 2 sources at the same time but can't visualize why it can be cause of an outage.

We removed the interface from the router and added static route to the FW.

[balaji.bandi]

This may be due to NAT overload, what FW and what Router / Switch here

Give us more information about your enviuronment  for us to understand the issue correctly

Explain in details, what is the issue before you shut and unshut, all network not able to go Internet or GW not pingable ?

[MHM Cisco World]

simply solve by make the DHCP server return the ONE ip address of GW to PC "router or FW".

this make PC when send traffic outside it subnet it send it to this only GW and also do only one ARP proxy.

now why FW reply to IP address that it not it interface IP because

NAT and for this config in FW NAT with keyword no-proxy-arp