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Changes in dhcpd.conf do not make a difference in DHCP service behaviour


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# 8  
The error happening here is clear. These are the relevant log lines:
Code:
Mar  7 16:19:30 trber dhcpd: No subnet declaration for eth0 (10.210.148.7).
Mar  7 16:19:30 trber dhcpd: ** Ignoring requests on eth0... 
Mar  7 16:19:30 trber dhcpd: Not configured to listen on any interfaces!
Mar  7 16:19:30 trber dhcpd: exiting.

This message means the local system has the given ip at the given interface. But there is no subnet declaration for that. The subnet declaration in your dhcpd.conf is:

Code:
subnet 172.17.126.192 netmask 255.255.255.224

The both does not match. You probably need to add a correct subnet declaration for the same net as the IP 10.210.148.7 is in. But you should not do that without knowing exactly what you are doing and what ip address range may be allowed and dedicated for that. Otherwise you'll disturb network operation in your network by probably causing ip address conflicts with static assigned ip addresses which are the same as in your subnet declaration.

---

Another Guess:

Maybe this is not the dhcp server which is serving the ip address of serverX and there is another dhcp-server active? As far as I see this dhcp-service is doing completely nothing because of the line: Mar 7 16:19:30 trber dhcpd: exiting..

You can check that by reviewing the system log of serverX and look for the ip/mac address of the dhcp-server serving the address.

You can also check with a packet sniffer(tcpdump) what's going on on the network and which ip-address is replying to dhcp-requests.(udp ports 67 & 68).

Last edited by stomp; 03-08-2019 at 08:15 AM.. Reason: Removed first part because it was a wrong guess.
# 9  
Quote:
Originally Posted by stomp
This message means the local system has the given ip at the given interface. But there is no subnet declaration for that. The subnet declaration in your dhcpd.conf is:

Code:
subnet 172.17.126.192 netmask 255.255.255.224

The both does not match. You probably need to add a correct subnet declaration for the same net as the IP 10.210.148.7 is in.

Is the subnet declaration supposed to be in same network as the IP 10.210.148.7 ? I dont think so. The DISCOVER is received via 172.17.126.195/194 and those IPs are in the defined network declaration in dhcpd.conf. A request is received from a defined network, so there should be an offer for it.

Code:
Mar  7 09:05:04 trber dhcpd: DHCPDISCOVER from XX:XX:XX:XX:45:06 via 172.17.126.195: unknown network segment
Mar  7 09:05:04 trber dhcpd: DHCPDISCOVER from XX:XX:XX:XX:45:06 via 172.17.126.194: unknown network segment

In the network, many devices will generate dhcp discover messages and all those messages will be relayed to the same server IP 10.210.148.7. According to the MACs in the received DISCOVER messages the 10.210.148.7 Server will give different IP addresses from different networks to each client.
Currently the subnet for the first MAC was entered in dhcpd.conf. At the end subnets for the others will be added too.
172.17.126.200 for MAC1
172.17.124.200 for MAC2
172.17.120.200 for MAC3
....
# 10  
Quote:
Is the subnet declaration supposed to be in same network as the IP 10.210.148.7 ? I dont think so. The DISCOVER is received via 172.17.126.195/194 and those IPs are in the defined network declaration in dhcpd.conf. A request is received from a defined network, so there should be an offer for it.
I'm not quite sure, but I would assume - according to the log entries - the listening interface should have at least an empty(=no leases) subnet declaration since the server is ignoring the interface and is exiting without one. Better check it yourself in the dhcpd manpage/documentation.

But if the dhcp server is actually getting the relayed dhcp/bootp requests my concern maybe not relevant.

--- Post updated at 02:04 PM ---

Maybe it is an option to run the dhcpd-server in foreground(-d) to check what configuration is active and what is going on. And to be sure the daemon is restarted at configuration changes.

Last edited by stomp; 03-08-2019 at 09:16 AM..
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# 11  
OS version

Code:
Red Hat Enterprise Linux Server release 6.8 (Santiago)

DHCP

Code:
DHCP Server 4.1.1-P1

# 12  
I 'll try with adding an empty dhcp entry for the interface network.

Code:
ddns-update-style none;

subnet 10.210.148.0  netmask 255.255.254.0 {}


Last edited by ekorgur; 03-11-2019 at 10:06 AM..
# 13  
Quote:
Originally Posted by ekorgur
I 'll try with adding an empty dhcp entry for the interface network.

Code:
ddns-update-style none;

subnet 10.210.148.0  netmask 255.255.254.0 {}

After the subnet decleration is added for the interface which is an entry useless for my solution, the DHCPD is UP and running properly.
DHCP gives OFFER for the incoming relayed requests from different subnets.
I hope the dummy entry for my interface IP does not cause an impact.

Thanks everybody.
This User Gave Thanks to ekorgur For This Post:
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