DHCP Relay

Hey, ah, so this bug is still there in v19. I expected this. We're having it since moving from v17 ti v18.

Sometimes DHCP Server on XG will fail, sometimes DHCP Relay to Windows Server will fail.

Re-Saving does not help on our XG, we need to delete and recreate a random DHCP Server or Relay to get it working again.

Have a case open currently but no technical feedback after weeks.

05158330 / 05128430

I ask you to open a case and refer to my case no#

do you have CheckMK?

We can see it in the DHCP Statistics on our Windows DHCP Server for Relay.

issue start= clients not getting DHCP address

issue fixed= we recreated one of a dozend DHCP Relays on XG

Likely it is actually a Flood Prevention of DHCP Relay and not a Bug.

The point is: DHCP Relay has a Builtin Feature called Flood Protection. 

If the DHCP Server was not reachable for the first DHCP requests, the relay will stop for some time to prevent a DHCP storm to the Servers. 

This prevents networks to go down from DHCP floods of requests which nobody answers. 

All the cases, i worked in, this was the case. The DHCP server was not reachable or did not answer for some reasons. 

And this screenshot actually makes me wonder: Why are there so many requests in this window? 

A Tcpdump of those requests in the affected area would help to see, who to blame. DHCP Relays work with the DHCP agent IPs. This means, if the server answers incorrectly, this could cause this. Only proveable in a tcpdump. 

Likely it is actually a Flood Prevention of DHCP Relay and not a Bug.

The point is: DHCP Relay has a Builtin Feature called Flood Protection. 

If the DHCP Server was not reachable for the first DHCP requests, the relay will stop for some time to prevent a DHCP storm to the Servers. 

This prevents networks to go down from DHCP floods of requests which nobody answers. 

All the cases, i worked in, this was the case. The DHCP server was not reachable or did not answer for some reasons. 

And this screenshot actually makes me wonder: Why are there so many requests in this window? 

A Tcpdump of those requests in the affected area would help to see, who to blame. DHCP Relays work with the DHCP agent IPs. This means, if the server answers incorrectly, this could cause this. Only proveable in a tcpdump. 

I have provided full network dumps to the case while the issue was happening.

we have IPS Flood protection disabled on that XG

This happens throughout the day. I would say from my monitoring, there were no enormous high DHCP requests.

The Flood Protection is not the UDP Flood Protection. Instead a Flood Protection of the own service. 

So if you have a tcpdump, you should see the incoming requests, the forwarded Requests with DHCP agent IP and the packets going back. Where is the issue sitting in terms of DHCP Relay? Why is the client still requests? 
You can read about DHCP Relays here: https://www.netmanias.com/en/post/techdocs/6000/dhcp-network-protocol/understanding-dhcp-relay-agents#:~:text=Relay%20Agent%20IP%20address%3A%20The,DHCP%20Discover%20message%20was%20received.