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Linux networking help


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I've got an Ubuntu 9.10 server on a network. The network has DNS and DHCP, and to access anything outside, going through an HTTP proxy is required. I've setup a static IP and all is fine locally, except I can't resolve any domain names from the server, not even the DHCP server. With dhclient, I can access the web through firefox (setup to use the proxy server for all connections), but I still cannot ping any domain names. I can use the "host" command and find out info about domains, but I can't ping the domain name nor the IP that it resolves to. If anybody has any idea of what could be wrong, or how I could troubleshoot the problem, please let me know.

/etc/networking/interfaces

auto lo
auto eth0
iface lo inet loopback
iface eth0 inet static
address 10.96.9.250
netmask 255.255.255.0
network 10.96.9.0
broadcast 10.96.9.255
gateway 10.96.9.6

/etv/resolv.conf (setup by dhclient)

domain ccsd.net
search ccsd.net
nameserver 10.49.16.34
nameserver 10.49.16.35

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What machines sit at the 10.49.16.34 + 10.49.16.35 addresses?

Nameservers should not be local machine ip addresses(10.x.x.x, 192.168.x.x, etc) unless you are getting your info from root.hints and forwarding the requests on behalf of the rest of the lan(in otherwords, a local dns machine, but a local dns machine still needs an outside dns service to do the queries for the lan to reach the internet)

Try adding 208.67.222.222 and 208.67.220.220 as name servers to the /etc/resolv.conf file and then see what happens. Those are OpenDNS servers adn shoudl work just fine.

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It seems as if no systems on the network can ping any address that's not local. This was not the case last time, if I remember correctly.

The addresses are what were given by the DHCP server. This is a school network and I'm not exactly sure how it all works. This is fine for now though, because it's only serving as a tool to help other students, as well as myself, learn Linux, programming, networking, etc.

When I set the OpenDNS servers as the nameservers, the domain names weren't even resolved, whereas they were with the previous setup, I just didn't receive any packets back.

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That explains it more, I thought you were doing this on a hoem network. Their dhcp server is sending those addresses for DNS then, and most likely, their network is filtering the traffic. you probably use local DNS servers on the lan that then forward the requests for you, and also filter what you are allowed to reach on the outside, beyond the lan. if the local dns servers are set only to resolve internal addresses, then you won't be able to get out to the internet using those servers. FF was probably using a proxy or getting data from a proxy monitoring for all port 80 requests. If port 80 is open, you can try to reach sites via telnet on port 80 to see if traffic can reach the internet, while monitoring all traffic with wireshark or such to see whats goign on. Even to a traceroute and see where the packets die, which is most likely somewhere in your lans perimeter.

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route add -net x.x.x.x netmask x.x.x.x gw x.x.x.x

I've got an Ubuntu 9.10 server on a network. The network has DNS and DHCP, and to access anything outside, going through an HTTP proxy is required. I've setup a static IP and all is fine locally, except I can't resolve any domain names from the server, not even the DHCP server. With dhclient, I can access the web through firefox (setup to use the proxy server for all connections), but I still cannot ping any domain names. I can use the "host" command and find out info about domains, but I can't ping the domain name nor the IP that it resolves to. If anybody has any idea of what could be wrong, or how I could troubleshoot the problem, please let me know.

/etc/networking/interfaces

auto lo
auto eth0
iface lo inet loopback
iface eth0 inet static
address 10.96.9.250
netmask 255.255.255.0
network 10.96.9.0
broadcast 10.96.9.255
gateway 10.96.9.6

/etv/resolv.conf (setup by dhclient)

domain ccsd.net
search ccsd.net
nameserver 10.49.16.34
nameserver 10.49.16.35

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The problem isn't access, I was just confused as to why I couldn't ping addresses to confirm the connection was working. I can still access the internet using FF, use apt-get, etc. I just cannot ping addresses. I'll talk to the Network Admin, but like you said digip, it seems like they're filtering ICMP requests.

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