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-   -   Ping resolves DNS but other apps don't? (http://www.linuxquestions.org/questions/linux-networking-3/ping-resolves-dns-but-other-apps-dont-532281/)

jago25_98 02-25-2007 01:26 PM

Ping resolves DNS but other apps don't?
 
Crucially:

"Connecting to irc.freenode.net (1.0.0.0) port 6667"
"[admin@(none) root]$ ping freenode.net
PING freenode.net (140.211.166.2): 56 data bytes
64 bytes from 140.211.166.2: icmp_seq=0 ttl=51 time=178.3 ms"

Separate ADSL Modem 192.168.1.10
- doesn't have much in the way of diagnostics. It's a linksys ADSL2 modem

^ connects through

Router 192.168.1.20
- /etc/resolv.conf is set to 192.168.1.10

^ connects through

Client PC 192.168.1.101
- Firefox doesn't resolve DNS queries. Konqueror kind of works but
slow DNS requests.
- yet, ping works fine resolving DNS perfectly
- /etc/resolve.conf is set to 192.168.1.20 (router), and ping only works if it is set to
this and not 192.168.1.10 (modem)
- gateway is set to router (192.168.1.20) by DHCP
- same symptoms on Windows and Linux, conected by ethernet cable
- can't ping the modem (192.168.1.10)
- apt-get fails to update as well

Other Windows only client PC:
- works fine connected by cable or wireless


What on earth is going on?

acid_kewpie 02-25-2007 01:32 PM

if i'm right, this sounds a lot like similar issues (well.. they wouldn't be similar otherwise would they??) which came down to very bizzare ipv6 issues with the adsl router and the certain patterns of dns lookups being done by clients. try disabling ipv6 on your box and see where that gets you. i still don't understand the "why", but the "how" seems to do the job.

fur 02-25-2007 02:18 PM

The linksys ADSL2 looks to be a combination modem, and router.

Then you have another router on top of that, and both are on the same subnet from what you posted

"Separate ADSL Modem 192.168.1.10"

"Router 192.168.1.20"

If NAT is enabled on two devices, and they share the same subnet there will most likely be problems. If you want to use both routers you will need to do some config changes on the 2nd device.

acid_kewpie 02-25-2007 02:24 PM

no, i don't think so. actually it was the 1.0.0.0 dns resolutions too that fitted in with it. regardless of network topology, if DNS works on one app on a client, it *should* work on all of them.

jago25_98 02-25-2007 02:31 PM

Thanks. For some strange reason I am able to get to linuxquestions.org but not google.co.uk ...

I am look for IPv6 in my WL500g settings and can't see a way to disable.

The modem only has one ethernet port on the back, and client PCs can't ping the modem.

What would be a better setup? -because the defaults of the modem and router being on 192.168.1.1 didn't seem to work.

acid_kewpie 02-25-2007 02:43 PM

it's not a function of the laptop, it's the operating system which dos the support. normally it's just a case of removing, or not loading the "ipv6" module on boot.

fur 02-25-2007 03:11 PM

Quote:

The modem only has one ethernet port on the back, and client PCs can't ping the modem.
Thats because they share they same subnet, and are being NATed by seperate devices.


Modem 192.168.1.10

Router 192.168.1.20


Any clients that are plugged into the router are not going to send their packets to 192.168.1.20 to reach 192.168.1.10, or any other IPs that share that subnet.

They will do a arp lookup asking who has 192.168.1.10, and wont get a answer because 192.168.1.10 is not a configured IP that is in their collision domain.


Now if the modem had a IP on another subnet then the clients would look in their routing table, and see that the IP is not on the same subnet they are, send packets to their default route of 192.168.1.20.

IPv6 may have something to do with this, but I have little experience with it. Either way, you will still want to get your network straightened out.

jago25_98 02-25-2007 03:22 PM

Thanks for the help guys! I changed the router to access point mode for the moment.

When I can would a choice of 10.0.0.1 for the modem and 192.168.1.1 for the router be ok? I'm not an expert in calculating subnets

fur 02-25-2007 04:01 PM

Do you have a link to documentation for you modem?

jago25_98 02-25-2007 04:06 PM

No, because it's 2nd hand off ebay and google search results are dogged by adverts

fur 02-25-2007 04:23 PM

Well I found the documentation, and that modem does do routing/NAT

ftp://ftp.linksys.com/international/...2MUE-EU_ug.pdf

This is what I would do.


To disable this.

In your modem go select "Bridged Mode Only"

Then click the "Save Settings" button.


This disables, routing, and NAT on the modem, so that it will act as a "normal" modem, and just pass traffic.



Then you would need to configure your router to connect to your ISP.

You want your router to perform NAT.

So it will connect to the ISP, and get a public IP on its external interface then hand out the 192.168.x.x IPs to your clients.


I would also get the documentation for your router as well as well as the connection settings for your ISP if you don't already have it.

acid_kewpie 02-25-2007 04:24 PM

/me sits back and waits for this to be deemed irrelevant. or be proved very very wrong. ;-)

fur 02-25-2007 04:39 PM

Quote:

Originally Posted by acid_kewpie
/me sits back and waits for this to be deemed irrelevant. or be proved very very wrong. ;-)


Well if you look here there was a similar issue with domains resolving to 1.0.0.0 with lynx, but ping would resolved the domain.

http://forums.whirlpool.net.au/forum...fm/474578.html


Either way his network is not setup properly with the 2 NATs like that, and needs fixed.


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