DNS Proxy on router - how to access other local machines?

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Plasmadog

40 posts

Geek

#68382 20-Sep-2010 19:23

Hi all.
I have a Linksys WAG54gp2, which has its DNS proxy enabled. In its config interface I can see a DNS entries table that is populated by all the machines currently connected, showing their host names and IPs. It seems to me that the point of that is to allow me to use the host names to resolve their IPs, but I cannot for the life of me figure out how that is done. On an Ubuntu box I try pinging one of the names in the list and it does not resolve. The Ubuntu box uses DHCP, and the router's address is listed as the primary DNS on that machine.
Can anyone tell me what I'm missing? Is there a domain name I should be using?

raytaylor

4014 posts

Uber Geek

Trusted

#382939 21-Sep-2010 23:18

Are there any firewall programs running on the other pc's?
The windows built in firewall allows incoming ping when set to home or lan mode but most others like norton, trend micro and avg will block it.

Can you ping www.google.co.nz from you ubuntu box?

Ray Taylor

There is no place like localhost

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Plasmadog

40 posts

Geek

#383037 22-Sep-2010 09:38

I don't really care if the ping gets through or not, so firewalls are not an issue. I just want to see the name being resolved to an IP, and that's not happening.

raytaylor

4014 posts

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#383114 22-Sep-2010 12:03

Ok ping doesnt really have anything to do with it - it just tests to see if there is communication between the computers.

In theory DNS proxy is just that - a proxy. Its not auctually a DNS server - though some modems call their dns servers proxys.
A proxy just takes your request, and forwards it on to your isp's dns server - which has no clue about the inner workings of your network. It may be that your router's is just a proxy and not a server.

So to get around this, windows computers use a service called WINS - windows internet naming service. Its sort of a peer to peer discovery system that was created in the days of wfw 3.11 as it didnt include tcp/ip installed by default and used the netbeui protocol.
I dont know if your ubuntu computer is capable of joining a wins group.

Are you sure your modem is showing you the list of computer names from its DNS server or dns proxy, rather than its DHCP list? DHCP does ask for a workstation name so that could be where its getting mixed up.

Ray Taylor

There is no place like localhost

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Plasmadog

40 posts

Geek

#383137 22-Sep-2010 12:52

Yeah, I just use ping as a quick way to check name resolution, as it always shows the actual IP it's sending to. Like I say, I don't care about the ping itself, so I could just as well use nslookup. Either way, the names of the local machines aren't resolving to anything.

I know about WINS, and about hosts files for that matter, so I can get to the local machines when I need to. I'm really just trying to determine whether or not the DNS proxy I already have makes those approaches redundant. It looks like it is supposed to, and if so I'd like to know how to use it.

The list of computers I see is labelled "DNS Entries Table", and has the option to manually add new entries (hostname/IP pairs). It is viewed by clicking a button labelled "DNS Entry", which is right next to the checkbox that enables/disables the DNS Proxy. How the list actually gets populated, I don't know, but there are entries there for devices that have a static IP, so it's not just from DHCP.

Maybe it is just a proxy that doesn't serve anything of its own. The manual says nothing about it either way. But in that case that list of local machines would not appear to have any purpose, so it seems unlikely.

raytaylor

4014 posts

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#383742 23-Sep-2010 18:28

You have probably already tested this, but on your ubuntu machine, do you have the modem set as the primary dns server and nothing else, like no secondary dns?
And can you then do an nslookup on both an internal and an external domain name or computer name?

Ray Taylor

There is no place like localhost

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Plasmadog

40 posts

Geek

#383961 24-Sep-2010 10:44

Mystery solved, I think. It seems that the DNS proxy does not do what I thought it did, so the question is moot.
I had Wireshark running last night as I was web surfing, and I noticed that all my DNS requests were being sent from the router back to my own PC. I turned off the DNS proxy and it stopped doing that. So it appears that it really is just a proxy, but before forwarding requests upstream it apparently tries all the local machines in turn, on the off-chance that one of them is running a DNS server. Seems a bit pointless to me, but at least I now know what it's doing.

Thanks Ray.

graemeh

2078 posts

Uber Geek

#383981 24-Sep-2010 11:16

So to take this one step further, is there an easy way to do what the OP wanted to do?

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raytaylor

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#384029 24-Sep-2010 13:21

yes
On the DHCP page of the modem, use a computer running a dns server on the local network as the primary server, and then as secondary, use your isp's dns server. This setting will be issued to all computers via dhcp or their manual configuration.

Disable dns proxy in the router, if you can do the above.

Or buy another modem.

Personally I just have one in half bridge and use a pc as my router.

Ray Taylor

There is no place like localhost

Spreadsheet for Comparing Electricity Plans Here

graemeh

2078 posts

Uber Geek

#384060 24-Sep-2010 13:58

raytaylor: yes
On the DHCP page of the modem, use a computer running a dns server on the local network as the primary server, and then as secondary, use your isp's dns server. This setting will be issued to all computers via dhcp or their manual configuration.

Disable dns proxy in the router, if you can do the above.

Or buy another modem.

Personally I just have one in half bridge and use a pc as my router.

Thanks. A bit more work than I was looking for as I don't want to add a server to the network.

I'll see if DD-WRT has a DNS server built in, it seems to have most other tricks sorted. :) Otherwise I'll probably just flag it.