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acshearer
New Member.
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dhcp.conf question

Hello,

I have a VM that is a DHCP server on one subnet, but it does not service anything on this subnet. It services my two other buildings that are on different subnets. It works and hands out IP address for those two buildings. The one thing I noticed, however, is in the dhcp.log file there is a lot of entries where computers on the same subnet as this server are looking at this server to get an IP address. It shows eth0: wrong network in the log file, likely because this server does not service this subnet. Computers that are on the same subnet as the DHCP server do get an IP address successfully but I wonder if it is looking at this one server first before going onto the other DHCP server that it is supposed to. I have the IP helper-address set on the routers.

I have this in the dhcp.conf file:

****************
authoritative;
subnet 10.194.192.13 netmask 255.255.255.255 {} (it would not start DHCP unless I set this, this is the IP address of the server but it does not serve this subnet)
*********************************
If a DHCP server is on a subnet that it does not service is there a way for the computers on that subnet to not even try to go to this DHCP server?

Thanks,
Andrew
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8 Replies
Knowledge Partner
Knowledge Partner

Re: dhcp.conf question

due to the very nature of the protocol clients broadcast. no way (and no reason) to change this. as the server doesn't have a pool defined for its local subnet it doesn't have anything to offer anyways, so the only "harm" will be an entry in the log.
b.t.w., i didn't know that the daemon loads with a declaration for its own address instead of its subnet.
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acshearer
New Member.

Re: dhcp.conf question

Thanks for the information. I was just asking because the Technician at that building on the subnet that the DHCP server does not service said that since I did this it takes hours to PXE boot now. So I wasn't sure if that was because the computers when they PXE are looking at this other DHCP server now and eventually moving on to the correct DHCP server.

Andrew
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Knowledge Partner
Knowledge Partner

Re: dhcp.conf question

You should really trace what's going on there. It might be worth a try to set the subnets you want to serve "authoritative" explicitely (i.e. on the subnet), while keeping the server "not authoritative" for its local subnet. IIRC you had declared a global "authoritative", so maybe the server is NAKing where it shouldn't.
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acshearer
New Member.

Re: dhcp.conf question

That would probably help since I did declare a global "authoritative". I have never done an explicit authoritative per subnet, in the dhcp.conf file how would I make just certain subnets authoritative? Do I put authoritative in the subnet statement?
Thanks,
Andrew
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Knowledge Partner
Knowledge Partner

Re: dhcp.conf question

The java console should do that for you. But yes, it should result in

not authoritative;

on top of the file and something like

subnet xx.xx.xx.xx netmask xx.xx.xx.xx {
max-lease-time xxxxxxxxxx;
authorititive;
.
.
.
}

in the subnet declaration.
Beware of any typos i may have made...
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acshearer
New Member.

Re: dhcp.conf question

Thanks I will try this out. I appreciate all your help.

Andrew
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acshearer
New Member.

Re: dhcp.conf question

Hello,

Doing what you stated by declaring authoritative by subnet only worked. Everything is back to normal.

Thanks,
Andrew
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Knowledge Partner
Knowledge Partner

Re: dhcp.conf question

thanks for the update. glad to hear it worked.
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