Re: Weird dhcp broadcast address

From: Ian Northeast (ian_at_house-from-hell.demon.co.uk)
Date: 05/29/04 

Date: Sat, 29 May 2004 11:38:04 +0100

On Sat, 29 May 2004 06:21:55 +0000, Bill Unruh wrote:

> We are getting some weird results from a dhcp connection. It is setting
> the eth0 IP address but with a broadcast address of 255.255.255.254 Now
> This just looks wrong. First I thought that it should have the IP&Netmask
> as its first digits (eg say the IP address is set to 111.222.112.5 with
> netmask 255.255.255.0, then the broadcast should start with 111.222.112
> Also since the gateway is 111.222.112.254, linux refuses to use what it
> seems to it to be the broadcast address as a gateway. I think this is
> proper behaviour, but is there some possibility that this dhcp setup is
> actually correct? Note that Windows seems not to care.

This is definitely wrong, if the address is 111.222.112.5 and the netmask
is 255.255.255.0, the broadcast is 111.222.112.255. It appears that this
DHCP server is set up incorrectly.

On my laptop which runs Debian Woody with dhclient, in the dhclient.leases
file I see that my (Solaris) DHCP server is giving out both netmask and
broadcast (correctly:) but there is still a record in there of the lease I
got from the (Windows) DHCP server when I last took it to work and this
shows it giving the netmask but not the broadcast. I don't recall
what the broadcast actually got set to but I do recall that it worked, and
the network number and netmask are such that if it had defaulted
"classfully" it shouldn't have - the number is "class A" and the netmask
/25. So I'm guessing it got calculated based on the netmask.

So, assuming this broken DHCP server isn't yours to fix, maybe configuring
your DHCP client not to request the broadcast address will fix it.

Regards, Ian

Relevant Pages

  • Re: Weird dhcp broadcast address
    ... > seems to it to be the broadcast address as a gateway. ... if the address is 111.222.112.5 and the netmask ... DHCP server is set up incorrectly. ...
    (alt.os.linux)
  • Re: Internet/LAN simulation
    ... > it to ping the 'internet' computer. ... I assume you can do it directly from your "real-internet" gateway machine? ... > netmask 255.255.255.0 ... > broadcast 1.1.1.255 ...
    (comp.os.linux.networking)
  • Re: Read from a file and then use command set
    ... echo "IP Address is: $ipaddress" ... echo "Netmask is: $Netmask" ... echo "Broadcast is: $Broadcast" ... echo "Gateway is: $Gateway" ...
    (comp.unix.shell)
  • Re: Read from a file and then use command set
    ... echo "IP Address is: $ipaddress" ... echo "Netmask is: $Netmask" ... echo "Broadcast is: $Broadcast" ... echo "Gateway is: $Gateway" ...
    (comp.unix.shell)
  • Re: Make a DHCP server using Fedora - Help
    ... that insisted on using 192.168.0.1 for the gateway PC. ... For the average home network, ... then the 255.255.255.0 netmask suffices. ... I would suggest that whatever PC you're running the DHCP server on ...
    (Fedora)
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