DHCP Across Wireless Bridge

Sun Dec 29 18:33:41 UTC 2013

Hi Glenn,

Thank you for the response!  I've done done a few tests using dhcpdump.
 Below are the results.

http://pastebin.com/Ns8jmzSu - This is a server-side dhcpdump showing my
Dish VIP722 DVR, connected via the wireless bridge, attempting to obtain an
address.

http://pastebin.com/9yMEUtLG - (Pair 1) Another server-side run of dhcpdump
showing a Lubuntu laptop, connected via the wireless bridge, attempting to
obtain an address.

http://pastebin.com/CrzfVJRd - (Pair 1) This is a client-side run of
dhcpdump showing the Lubuntu laptop, connected to the wireless bridge,
attempting to obtain an address.  It never receives a DHCPOFFER response.

http://pastebin.com/LrRD1wac - (Pair 2) This is a server-side run of
dhcpdump showing the Lubuntu laptop, hardwired to the network normally (NOT
using the wireless bridge), successfully obtaining an address.

http://pastebin.com/EjVszsMS - (Pair 2) And lastly, this is a client-side
run of dhcpdump showing the Lubuntu laptop, hardwired to the network
normally (NOT using the wireless bridge), successfully obtaining an address.

It looks like the wireless bridge is preventing the DHCPOFFER response from
reaching the client.  The DHCPDISCOVER broadcast is received by the DHCP
server with the MAC address of the wireless bridge as the source.  The
DHCPDISCOVER broadcast has a request to redirect the response to the MAC
address of the client, which it looks like the DHCP server is obeying this
request.  But, for some reason, the DHCPOFFER response never makes it to
the client.

Is there a way I can configure isc-dhcp-server and/or the OS it's running
on to work around this?  The Cisco DHCP server seems to do things
differently that makes this a non-issue.  Could it be that the DHCPOFFER
needs to have a destination of the wireless bridge with a redirect request
to the MAC address of the client?  I don't know...

Thanks for the pointers on my configuration. I fixed the dynamic address
range so that it does not include the broadcast address (oops!), and I
modified the fixed address for host dwight so that it's outside the dynamic
address range.  It didn't help this particular problem, but it's always
good to follow best practice.

~ Anthony

On Sun, Dec 29, 2013 at 2:40 AM, Glenn Satchell
<glenn.satchell at uniq.com.au>wrote:

> Hi Anthony
>
> That config looks like it should be ok. As you are seeing the discover
> packets, then traffic is getting through from the clients and the dhcp
> server is replying. However the next thing should be a dhcp request packet
> from the client which you're not seeing.
>
> Can you run a packet capture on a client connected to the wireless bridge
> and see which parts of the traffic you can see? What you'd be looking for
> is whether the client sees the offer from the dhcp server, and if it does
> whether it then sends a dhcp request back to the server.
>
> Perhaps also try a packet capture on the dhcp server to see if the request
> is coming in, but is somehow not accepted by the dhcp server daemon.
>
> Two minor things with the config: the top end of the range is the
> broadcast address (10.7.17.255), perhaps reduce that to 10.7.17.254. The
> host dwight has a fixed ip address that is inside the dynamic range. While
> it may never be a problem, it's better to either break the range around
> that address (have two ranges: 100-199 and 201-254) or change it to have
> an ip outside the dynamic range. Neither of these two problems would stop
> dhcp working though.
>
> regards,
> -glenn
>
> On Sun, December 29, 2013 6:36 pm, Anthony Hoppe wrote:
> > Hello All,
> >
> > I've been experimenting with isc-dhcp-server on my home network and have
> > run into a snag.  I have three devices (Xbox 360, Samsung Blu-Ray Player,
> > and a Dish VIP 722 HD-DVR) connected to a switch which connects to a
> > wireless bridge.  In my previous setup (using my Cisco 871 router running
> > C870-ADVIPSERVICESK9-M ver 12.4(24)T as a DHCP server) these devices were
> > able to receive DHCP addresses without any problems.  However, with
> > isc-dhcp-server, they are unable to receive addresses.  Reviewing
> > /var/log/syslog shows many DHCPDISCOVER/DHCPOFFER pairings as seen below
> > (an example of one device):
> >
> > -----
> >
> > Dec 28 23:28:13 dns dhcpd: DHCPDISCOVER from 00:08:89:e4:dd:df via eth0
> > Dec 28 23:28:13 dns dhcpd: DHCPOFFER on 10.7.17.101 to 00:08:89:e4:dd:df
> > via eth0
> > Dec 28 23:28:15 dns dhcpd: DHCPDISCOVER from 00:08:89:e4:dd:df via eth0
> > Dec 28 23:28:15 dns dhcpd: DHCPOFFER on 10.7.17.101 to 00:08:89:e4:dd:df
> > via eth0
> > Dec 28 23:28:17 dns dhcpd: DHCPDISCOVER from 00:08:89:e4:dd:df via eth0
> > Dec 28 23:28:17 dns dhcpd: DHCPOFFER on 10.7.17.101 to 00:08:89:e4:dd:df
> > via eth0
> > Dec 28 23:28:31 dns dhcpd: DHCPDISCOVER from 00:08:89:e4:dd:df via eth0
> > Dec 28 23:28:31 dns dhcpd: DHCPOFFER on 10.7.17.101 to 00:08:89:e4:dd:df
> > via eth0
> > Dec 28 23:28:33 dns dhcpd: DHCPDISCOVER from 00:08:89:e4:dd:df via eth0
> > Dec 28 23:28:33 dns dhcpd: DHCPOFFER on 10.7.17.101 to 00:08:89:e4:dd:df
> > via eth0
> > Dec 28 23:28:35 dns dhcpd: DHCPDISCOVER from 00:08:89:e4:dd:df via eth0
> > Dec 28 23:28:35 dns dhcpd: DHCPOFFER on 10.7.17.101 to 00:08:89:e4:dd:df
> > via eth0
> > Dec 28 23:28:49 dns dhcpd: DHCPDISCOVER from 00:08:89:e4:dd:df via eth0
> > Dec 28 23:28:49 dns dhcpd: DHCPOFFER on 10.7.17.101 to 00:08:89:e4:dd:df
> > via eth0
> > Dec 28 23:28:51 dns dhcpd: DHCPDISCOVER from 00:08:89:e4:dd:df via eth0
> > Dec 28 23:28:51 dns dhcpd: DHCPOFFER on 10.7.17.101 to 00:08:89:e4:dd:df
> > via eth0
> > Dec 28 23:28:53 dns dhcpd: DHCPDISCOVER from 00:08:89:e4:dd:df via eth0
> > Dec 28 23:28:53 dns dhcpd: DHCPOFFER on 10.7.17.101 to 00:08:89:e4:dd:df
> > via eth0
> >
> > -----
> >
> > Connecting a known working computer to the switch behind the wireless
> > bridge also results the same...it is not able to obtain a DHCP address.
> >  DHCP works anywhere else on the network without a hitch.
> >
> > Some Googling around leads me to believe the culprit is likely the
> > wireless
> > bridge.  I am using an EnGenius WAP (I can't find and/or recall the model
> > at the moment) in client bridge mode.  However, like I said earlier, DHCP
> > worked fine in my previous setup.  Is there a way to configure
> > isc-dhcp-server so that it will work, too?
> >
> > Here is my dhcpd.conf:
> >
> > -----
> >
> > authoritative;
> > option domain-name "hhsn.net";
> > option domain-name-servers 10.7.17.24;
> >
> > ddns-updates on;
> > ddns-update-style interim;
> > ignore client-updates;
> > update-static-leases on;
> >
> > default-lease-time 86400;
> > max-lease-time 86400;
> > log-facility local7;
> >
> >
> > include "/etc/dhcp/ddns.key";
> >
> > zone hhsn.net. {
> >   primary 10.7.17.24;
> >   key DDNS_UPDATE;
> > }
> >
> > zone 17.7.10.in-addr.arpa. {
> >   primary 10.7.17.24;
> >   key DDNS_UPDATE;
> > }
> >
> >
> > subnet 10.7.17.0 netmask 255.255.255.0 {
> >         range 10.7.17.100 10.7.17.255;
> >         option routers 10.7.17.1;
> >         option broadcast-address 10.7.17.255;
> >         option subnet-mask 255.255.255.0;
> > }
> >
> > host dwight {
> >  hardware ethernet 00:23:DF:7F:28:04;
> >  fixed-address 10.7.17.200;
> > }
> >
> > host nettalk {
> >  hardware ethernet 00:25:F6:00:3A:B4;
> >  fixed-address 10.7.17.20;
> > }
> >
> > -----
> >
> > Any assistance would be greatly appreciated.  I am using isc-dhcp-server
> > version 4.2.2 on Debian 7.
> >
> > Thanks!
> >
> > ~ Anthony
>
>
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