dhcpd assign duplicated IP address

[Zhang Weiwu]

Bill Moran 写道:
> In response to Zhang Weiwu <zhangweiwu at realss.com>:
>
> <snip>
>   
>> P.S. In recent days we some times got another network problem and I'm
>> not sure if it's related to this DHCP server behavior. It happens on
>> both Linux and Windows hosts that a host suddenly is no longer
>> accessible (Ping no response). Check 'arp -a' on other hosts shows the
>> host being accessed have wrong Mac Address. e.g. yesterday
>> 218.193.55.195 suddenly become in-accessible, this host is Linux and we
>> got this behavior on a nearby host:
>>
>> sappho # arping 218.193.55.195
>> Unicast reply from 218.193.55.195 [00:0F:EA:4B:82:58]  0.638ms
>> Unicast reply from 218.193.55.195 [00:0F:EA:4B:82:58]  0.637ms
>> Sent 113 probes (1 broadcast(s))
>> Received 113 response(s)
>> sappho # arp -a 218.193.55.195
>> ? (218.193.55.195) at 00:02:2A:C1:53:87 [ether] on eth0
>>
>> arping reply is different from arp cache. This host become accessible
>> the next day. Strange. Are these two problems related?
>>     
>
> You have something seriously wrong somewhere.  They may be related but
> there's not enough information here to be sure.  Consider installing
> arpwatch on one or more systems and see if the reports it sends narrow
> down the problem.
I have followed Jeffrey's suggestion and reconfigured dhcpd.conf to make 
sure no host with specified IP address is within dynamic assigned IP 
range. I was mislead by my previous experience with Microsoft DHCP 
server configuration where a host with fixed IP address should be within 
the range. After updated dhcpd.conf I haven't see an IP conflict yet, 
I'll watch a few days.

For the ARP issue, thanks for suggesting arpwatch. I'd like to take a 
deeper look into how ARP works later. Thanks!