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DORA between a client and unknown DHCP server

ml flag

I have an isc-dhcp-server installed on an Ubuntu VM that has 2 interfaces connected to VM Client1 Centos & VM Client2 Ubuntu. There are 3 networks: Client1 & DHCP, Client2 & DHCP, and Client1 & Client2.

Topology

How come I have DORA between the clients and IP x.x.x.3 DHCP server instead of x.x.x.254 IP's that are assigned static to DHCP server interfaces that are also default gateway IP's.

UPD: I am still able to get an IP from this IP x.x.x.3 DHCP server even if the main x.x.x.254 IP DHCP is down.

ru flag
perhaps don't use acronyms that some might not know. what's "DORA"? (for those who don't know how DHCP works)
Harrier Panels avatar
ml flag
DHCP session: DISCOVER - OFFER - REQUEST - ACKNOWLEDGE
Harrier Panels avatar
ml flag
It looks like now each client has its own DHCP server running from which it gets its IP. `ip n` shows it as "dev enp0s3 lladdr".
ru flag
Did you check each system to make sure it doesn't have a DHCP server configured/installed on them? The behavior you're expecting here sounds like each system has its own DHCP server. You should only have *one* DHCP network for the entire environment, or ignore DHCP and static-IP your systems. Having multiple DHCP servers and interconnectivity like this without proper firewalling/relaying/etc. setups can result in this breakage. (also I know what DORA is, but others might not :P)
Harrier Panels avatar
ml flag
Thomas thanks! Sorry didn't take this into account someone might mot know but probably he/she could not help in this case. The problem is I did not install any DHCP server on the virtual machines so such a behavior looks strange to me. Do not have any clue where the x.x.x.3 DHCP comes from and how to locate it. Any help would be much appreciated.
Harrier Panels avatar
ml flag
Changed Net1 & Net2 (see the picture) to y.y1.y.0/24 and y.y2.y.0/24 accordingly and now the clients get their IP's as usual however this 'ghost' DHCP server still keeps offering its network IP's. Maybe it's the kernel issue that had arisen when I first tried setting up the DHCP server.
ru flag
start by going to your sysotem and running `sudo dhclient -4 -v` and give us the output? That will help you ID which server/sstem is reporting to you with the offer. That'll allow you to track a little bit *where* your DHCP is being ahndled by.
Harrier Panels avatar
ml flag
Thanks! It might have helped but I've already rearranged everything. I suppose the problem could have occurred because I previously set up NAT Networks with the same IP's and connected the VM's to them. Then I re-linked them with Internal Networks.
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