BRX not broadcasting MAC-address

[Kristjan]

For this customer we have a number of PLCs (DL and BRX) on several different sites. The IT guys want to have better control over their network and instead of us using static IP-addresses, they will reserve IP-addresses for our specific PLC MAC-addresses

Today I was connecting a BRX to their network through the native ethernet port on a BRX18. I had the port setup for static IP address. The customer's IT department has configured the switch to reserve the IP-address and associate it with the PLCs MAC address. When I connected the BRX to their switch, the BRX apparently didn't broadcast its MAC-address and the connection was unsuccessful.

When I changed the ethernet port to DHCP (and set appropriate DNS), the MAC address was broadcasted and the system now works as intended.

Now my question is: Must the BRX ethernet port be set up with DCHP (and DNS) for the MAC address to be broadcasted?

[BobO]

For this customer we have a number of PLCs (DL and BRX) on several different sites. The IT guys want to have better control over their network and instead of us using static IP-addresses, they will reserve IP-addresses for our specific PLC MAC-addresses

Today I was connecting a BRX to their network through the native ethernet port on a BRX18. I had the port setup for static IP address. The customer's IT department has configured the switch to reserve the IP-address and associate it with the PLCs MAC address. When I connected the BRX to their switch, the BRX apparently didn't broadcast its MAC-address and the connection was unsuccessful.

When I changed the ethernet port to DHCP (and set appropriate DNS), the MAC address was broadcasted and the system now works as intended.

Now my question is: Must the BRX ethernet port be set up with DCHP (and DNS) for the MAC address to be broadcasted?

What do you mean by broadcasting the MAC?

[Kristjan]

Broadcast is probably not the proper term 

Seems like the PLC wasn't telling the switch its MAC-address. The switch did not see any MAC-address on the device (PLC) that was connected.

It wasn't until I changed to DHCP (and set DNS) that the switch saw the MAC-address.

So I guess there is nothing wrong with the setup, I just want to better understand the setup and if it is neccessary to run DHCP (and/or DNS) when we are in an environment where IP-addresses are reserved and allocated to specific MAC-addresses.

PS. Of course there are all kinds of rules and policies in place on the network. I am by no means a networking expert, I choose to leave it to the people that network for a living.

[BobO]

Broadcast is probably not the proper term 

Seems like the PLC wasn't telling the switch its MAC-address. The switch did not see any MAC-address on the device (PLC) that was connected.

It wasn't until I changed to DHCP (and set DNS) that the switch saw the MAC-address.

So I guess there is nothing wrong with the setup, I just want to better understand the setup and if it is neccessary to run DHCP (and/or DNS) when we are in an environment where IP-addresses are reserved and allocated to specific MAC-addresses.

PS. Of course there are all kinds of rules and policies in place on the network. I am by no means a networking expert, I choose to leave it to the people that network for a living.

The PLC doesn't talk talk to the switch explicitly; it responds to or sends requests. The MAC address is contained in the frame and the the switch determines the MAC from the frame. The switch should be routing all traffic to the port until it determines what the MAC is. With DHCP, the PLC initiates traffic which I guess preemptively gives the switch the MAC, but that shouldn't be required to work.

If the switch is managed, perhaps there is some setting that is affecting this.

You could also add code to the PLC to send a broadcast packet at some slow interval. That would force the switch to see the MAC.

[Kristjan]

Thanks for the explanation 

I will try sending a broadcast packet next time I face this issue.