Friday, May 3, 2019

What gateway are devices using - Cisco Router

My companies standard is to use x.x.x.1 as the default gateway for a subnet. We bought a company that uses x.x.x.254.

A coworker replaced the router a while ago at one of their warehouses and did this...

 interface GigabitEthernet0/0.5 description Data_vlan encapsulation dot1Q 5 ip address 192.168.5.254 255.255.255.0 secondary ip address 192.168.5.1 255.255.255.0 

He also changed dhcp to hand out .1 as the default gateway.

Here is my problem, there is still a random mix of static devices out there that use .254 as the default gateway and I want to remove .254 from the config.

I know I can log into each static device manually and look at the network config or remove the gateway and see what breaks but this situation got me thinking. I have no idea how I would be able to tell what gateway is used by what device from the router or another tool. Even a packet capture will only show the destination MAC address but the same MAC is used by both gateway IP addresses...

cvg0rtr01#sh ip arp Protocol Address Age (min) Hardware Addr Type Interface Internet 192.168.5.1 - f8c2.889d.b00b ARPA GigabitEthernet0/0.5 Internet 192.168.5.254 - f8c2.889d.b00b ARPA GigabitEthernet0/0.5 

Anyone have any ideas on how to track what the default gateway is set to on a device without logging into it? I'm mostly just curious.



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