DHCP & DNS [OT]

Tue Oct 30 09:44:43 UTC 2007

zephod at cfl.rr.com wrote:
> As promised, here are the results of my experiments on putting a DNS server on my Linksys router. 
> 
> After a little research I found the DD-WRT project (http://www.dd-wrt.com/) which looked like it would do what I wanted by using the DNS forwarder (DNSmasq) feature. 
> 
> A quick read of the documentation makes you very aware of the term "bricking" your router, ie flashing the router firmware incorrectly, thereby totally and possibly irrecoverably breaking it. So after a second, thorough read of the documentation, taking the precautions of noting all of the current settings of the router and copying the online instructions to local files, I sucessfully flashed the router with the mini version of the DD-WRT firmware. There are warnings about only using IE to upgrade from the original Linksys firmware. The warnings may be out of date now, but I heeded them anyway. Once the DD-WRT firmware is installed, any browser can be used for futher upgrades. I got a scare at first because I couldn't log in to the router after I had upgraded. Then I remembered, that DD-WRT uses root as the default login instead of nothing.
> 
> Next, I configured the router according to my old settings and activated DNSmasq. Everything appeared to be working correctly. I could browse the internet from both my Fedora box and the Vista box. I could also ping the Vista box or the router from the Fedora box just by typing 'ping Vista' or ping DD-WRT. 
> 
> I did manage to screw someyhing up while I was feeling very pleased with myself and poking around the various screens. The router somehow lost the host name of my Fedora box and I could no longer ping myself. I tried restarting networking, rebooting the router and rebooting the Fedora box with no luck. Eventually, I was able to get it back by creating a dhclient.conf file and putting a send hostname clause it in. It still worked when I deleted the dhclient file, so I don't really know what was happening there.
> 
> Now the only remaining problem was that the Windows box could not ping either itself, the router or the Fedora box. I found the answer in the DNSmasq FAQ. Apparently, Windows machines do not use DNS when looking up machine names that don't contain a '.', they just try to use WINS. This can be verified by typing 'ping my_local_machine' which will fail and 'ping my_loca_machine.' which suceeds. The solution is to set a domain name in the DHCP server and use the domain-required and expand-hosts options. The Windows machine must also be set up to use 'mydomain' DNS suffix for this connection. Now, when I type 'ping DD_WRT' from either the Fedora box or the Windows box, I get a response from host.mydomain. Here is the windows results:
> 
> C:\> ping DD-WRT
> 
> pinging DD-WRT.mydomain [192.168.1.1] with 32 bytes of data :
> 
> Reply from 192.168.1.1: bytes=32 time=1ms TTL=64
> Reply from 192.168.1.1: bytes=32 time=1ms TTL=64
> Reply from 192.168.1.1: bytes=32 time=1ms TTL=64
> Reply from 192.168.1.1: bytes=32 time=1ms TTL=64
> 
> Ping statistics for 192.168.1.1 :
>    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss)
> Approximate round trip time in ms:
>    Minimum = 1ms, Maximum = 1ms, Average = 1ms
> 
> Now the only problem left, and it's not really a problem, just a curiousity, is that the Windows box cannot ping itself. I might try to update to the standard version of the firmware next weekend.
> 
> If anybody would like more details, just let me know.

As one who has a Linksys wrt54g (one of those revisions that's 
compatible) I'm very interested in this, and any more information you 
can offer.

In particular, what can you do now that you couldn't before?

I've been sorely tempted to upgrade it to non-linksys firmware; one of 
the problems I have is it tends to die under load, requiring a reset, 
and if there's nobody around, a reset is fairly inconvenient.

> 
> Steve
> 
> ---- zephod at cfl.rr.com wrote: 
>> It seems like the solution is to set up a local DNS server on the same machine as the the DHCP server. Some people suggested putting the DHCP server on the Fedora box but it is usually not on during the day which would be a problem for the Windows box which usually is. I'm going to do a little research and see if I can put a DNS server on the Linksys.
>>
>> Thanks to all who responded on this. I'll report back on my progress.
>>
>> Steve
>>
>> ---- Adalbert Prokop <adalbert.prokop at gmx.de> wrote: 
>>> zephod at cfl.rr.com wrote on Sunday 21 October 2007:
>>>
>>>> Here is my simple and, I suspect, very common setup: 2 PCs, one FC6
>>>> Linux, one Windows Vista and a Linksys wireless router. A DHCP server
>>>> on the Linksys determines the IP addresses of the 2 machines.
>>>> My question is: is it possible for either machine to ping the other
>>>> without having to make an entry in its local hosts file?
>>> At least not only with DHCP. It is only for assigning IP addresses and 
>>> parameters to network devices. If you want name-to-address resolving you 
>>> need (an internal) DNS server. That could be your Linksys router. I don't 
>>> know if the original firmware has a DNS server, but WRT54G is flashable. 
>>> That means you can install a small Linux distro on it and within a DNS 
>>> server (dnsmasq or bind or ...). Look here
>>>
>>> http://www.freewrt.org/trac/wiki/Documentation/TargetSystems
>>>
>>> If you cannot use a DNS server you could use Bonjour/Zeroconf for address 
>>> resolving. Apples Bonjour is available for Windows and Linux has its own 
>>> implementations of the mDNS (multicast DNS) protocoll, e.g. mDNSresponder 
>>> or avahi. mDNS is simmilar to DNS but it does not need a central server 
>>> because every machine is sending broadcast messages on the network 
>>> announcing itself to its neighbours. With help of the nss-mdns package 
>>> you can then resolve the broadcasted names to IP addresses.
>>>
>>> For a small office the DHCP/DNS solution is the preferable one.
>>>
>>> -- 
>>> bye,
>>> Adalbert
> 

-- 

Cheers
John

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