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Friday, December 07, 2012

Testing DHCPv6

I've been doing some research into DHCPv6 for a client and beyond the talk and text, I needed some hands on testing. I can create a DHCPv6 server on a Cisco router in GNS3, but who knew creating a DHCPv6 client would be so troublesome.

I suppose I could have just used my Windows 7 x64 host and connected to the GNS3 simulation on a loopback interface. I've done this before, but I was looking for a way to do this in the simulation. I took a look at the Tiny Core 3.8.2 linux Qemu image available on the GNS3 appliances page and gave it a go. Unfortunately, Tiny Core uses 'udhcpc' as the DHCP client and it only supports IPv4. Partial success.

I had a look at Tiny Core and found that you can load packages and one package was the ISC DHCP package version 4.2.1 including client, server and relay. According to their website, 4.2.1 supports IPv6 so I thought I'd pursue.

The first step was to get the ISC DHCP package installed. Tiny Core comes with a package manager; however, you need to be online to use it and I hadn't played with the Qemu emulator (to run Tiny Core) outside of GNS3. To get network access, Qemu needs a TAP interface, which isn't available on Windows. I had to get one.

OpenVPN offers Windows software that comes with - among other things - a TAP interface driver. So simply download the latest Windows intstaller and run it. Luckily, it asks what components you'd like to install. I unchecked everything except for the Tunnel TAP interface driver. Once the install was completed, I had a new interface under Network and Sharing Center - Adapters, which I renamed to "TUN-TAP".

Simply select my physical NIC - in my case my wireless card - and the new TUN-TAP interface, right-click and select "Bridge Connections".

Armed with my new interface, I was able to launch Qemu and get Tiny Core online to add the proper packages:

C:\> qemu -hda linux-tinycore-3.8.2.img -net nic -net tap,ifname=TUN-TAP

Once loaded, I used the AppBrowser, pressed the "Connect" button and the available packages loaded. I used the search to look for "dhcp" and found "isc-dhcp.tcz". I selected "OnBoot" and pressed "Go". It installed the prerequisites and finished.

Next, I had to change Tiny Core to use 'dhclient' instead of 'udhcpc' and make the change permanent over reboots. First, I edited the "/etc/init.d/dhcp.sh" file. I commented out the line with 'udhcpc' and added two new lines after it:

/usr/local/sbin/dhclient    -sf /usr/local/sbin/dhclient-script $DEVICE >/dev/null 2>&1 &
/usr/local/sbin/dhclient -6 -sf /usr/local/sbin/dhclient-script $DEVICE >/dev/null 2>&1 &

That will load 'dhclient' (ISC DHCP client) instead of 'udhcpc' and it will do it for all interfaces and for both IPv4 and IPv6.

Finally, to make the change permanent, I edited the "/opt/.filetool.lst" file. I removed the line with "/sbin/dhclient" and replaced with:


and then ran 'filetool' and did a "Backup". Curiously, I got an error saying the backup failed, but examining the "/mnt/hda1/tce/mydata.tgz" file, I found the "/etc/init.d/dhcp.sh" file with my edits. So, I shutdown and restarted and hoped for the best.

It worked! I verified 'dhclient' was running instead of 'udhcpc':

tc@box:~$ ps -ef | grep dhc
 1562 root     /usr/local/sbin/dhclient -sf /usr/local/sbin/dhclient-script eth0
 1699 root     /usr/local/sbin/dhclient -6 -sf /usr/local/sbin/dhclient-script eth0
 1762 tc       grep dhc

The final test was to check DHCPv4 and DHCPv6 functionality in the GNS3 simulation. I had a 7200 series router configured as a DHCPv4 and DHCPv6 server and connected a Qemu host with the newly updated Tiny Core image. The host booted in the simulation and got both an IPv4 and IPv6 address. This was verified on the router by looking at:

R1>show ip dhcp binding
Bindings from all pools not associated with VRF:
IP address      Client-ID/          Lease expiration       Type
                Hardware address/
                User name   00ab.298c.3e00      Dec 07 2012 03:48 PM   Automatic
R1>show ipv6 dhcp binding
Client: FE80::2AB:29FF:FE8C:3E00
  DUID: 000100011855208300AB298C3E00
  Username : unassigned
  IA NA: IA ID 0x298C3E00, T1 43200, T2 69120
    Address: 2001:DB8:A64:6800:9D60:EF10:536A:28BF
            preferred lifetime 86400, valid lifetime 172800
            expires at Dec 09 2012 11:47 AM (172618 seconds)

The one thing to remember is that Qemu doesn't save any changes to the actual image file when in a GNS3 simulation. All changes are saved to a FLASH disk in the working directory. If that file or directory is removed, the Qemu host is back to defaults. I learned this the hard way the first time through. The answer is to load any packages and make any edits by running Qemu itself - as shown in the first command of this post - and then using the updated image in the GNS3 simulation.

NOTE: You can do the same for Micro Core linux by using the command line AppBroswer 'ab' and using the 'filetool.sh -b' command to commit the changes.

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