DHCP and 2 subnets

Chris Arnold carnold at electrichendrix.com
Mon Apr 7 02:33:40 UTC 2008


On Sunday 06 April 2008 06:42:51 pm Simon Hobson wrote:
> Yes, that looks OK, but you can make life easier for yourself with
> some formatting ;-) Also, you can move common options (like the lease
> times) to the global scope. So you could end up with :

Done

> That sounds pretty standard. What is logged when a 192.168.123.x
> client gets the wrong address ? Also, it may be worth using a sniffer
> (like wireshark) to see what packets are being passed on the networks
> concerned.

This gets logged to the dhcp server:
Apr  6 22:12:51 mail dhcpd: DHCPDISCOVER from 00:0b:db:c8:f1:71 (Izabella) via 
eth1
Apr  6 22:12:51 mail dhcpd: DHCPDISCOVER from 00:0b:db:c8:f1:71 (Izabella) via 
192.168.123.2
Apr  6 22:12:51 mail dhcpd: DHCPREQUEST for 192.168.124.144 (192.168.124.1) 
from 00:0b:db:c8:f1:71 (Izabella) via 192.168.123.2: ignored (not 
authoritative).
Apr  6 22:12:51 mail dhcpd: ICMP Echo reply while lease 192.168.124.144 valid.
Apr  6 22:12:51 mail dhcpd: Abandoning IP address 192.168.124.144: pinged 
before offer
Apr  6 22:12:52 mail dhcpd: DHCPOFFER on 192.168.123.253 to 00:0b:db:c8:f1:71 
(Izabella) via 192.168.123.2

This seemed to me to "cached" somewhere so i restarted and this restart is the 
above log.
Also, i have configured dhcp relay on 1 of our windoze servers that is on 
192.168.123 network. Nothing gets logged at that server and when i had the 
router configured for dhcp relay, nothing got logged at that device either.
This is logged at the 192.168.123.x client on a reboot:
Apr  6 22:12:13 Izabella ifup-dhcp:     eth0      (DHCP) 
Apr  6 22:12:13 Izabella ifup-dhcp: . 
Apr  6 22:12:13 Izabella kernel: NET: Registered protocol family 17
Apr  6 22:12:14 Izabella ifup-dhcp: . 
Apr  6 22:12:14 Izabella kernel: e1000: eth0: e1000_watchdog_task: NIC Link is 
Up 100 Mbps Full Duplex, Flow Control: RX
Apr  6 22:12:14 Izabella kernel: ADDRCONF(NETDEV_CHANGE): eth0: link becomes 
ready
Apr  6 22:12:15 Izabella ifup-dhcp: . 
Apr  6 22:12:19 Izabella syslog-ng[2019]: last message repeated 2 times
Apr  6 22:12:19 Izabella ifup-dhcp: no IP address yet... backgrounding. 
Apr  6 22:12:53 Izabella ifup:     eth0      device: Intel Corporation 82540EM 
Gigabit Ethernet Controller (rev 02)
Apr  6 22:19:21 Izabella ifprobe:     eth0      changed config file: 
ifcfg-eth0 --> restart interface!
Apr  6 22:19:21 Izabella ifdown:     eth0      device: Intel Corporation 
82540EM Gigabit Ethernet Controller (rev 02)
Apr  6 22:19:21 Izabella dhcpcd[4929]: terminating on signal 15

> I don't understand what you mean by : "I have the router config set
> to point to the gateway of the 192.168.123.x network"
>
>
> But from the description, the Netscreen DHCP Relay agent sound normal.

On the router in the dhcp relay option there is a place to provide an ip 
address. I assume this will need to be pointed to the dhcp server. In the 
above statement, i had it pointed to the gateway of the 192.168.123 network 
which, i believe is not right. So i changed it to point to the dhcp server. I 
will try to attach a screen shot to this email. Thanks again for all your 
help.


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