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txu Beginner
Beginner

Can ping IP address but not by domain name. A DNS issue?

Hi,

I'm pretty new to business-level routers (I have programming and certain Ubuntu system admin experience though) but I'm facing a problem with Cisco 4431 router.

 

We have a client with quite strict security policy. The router resides in client's network, with external IP (12.34.56.78) assigned by client's network. The router manages a few Ubuntu servers with v16.04 (X, Y, Z, etc).

 

From my computer at my home, I can log into client's VPN and then access the router with ssh command, like

>ssh admin@12.34.56.78

or access server X with command like

>ssh -p 2210 guest@12.34.56.78

 

When I ssh into X, I issue command

>wget https://www.gnu.org/software/wget    # I have wget installed actually, just to test internet connection

I got error like

>wget: unable to resolve host address: 'ftp.gnu.org'

 

Previously I thought the issue was due to the firewall. Please refer to my previous post:

https://community.cisco.com/t5/routing/commands-to-check-internet-connection-for-cisco-4431-integrated/m-p/3860660/highlight/false#M315434 

 

I think I've set the networking files like "interfaces" correctly on server X, like below

 

user@reporter:/etc/network$ more interfaces

# This file describes the network interfaces available on your system

# and how to activate them. For more information, see interfaces(5).

source /etc/network/interfaces.d/*

# The loopback network interface

auto lo

iface lo inet loopback

# The primary network interface

auto eno1

iface eno1 inet static

address 192.168.2.10 -------------Note: this is the internal IP of the server I'm on now

gateway 192.168.2.1 -------------Note: this is the internal IP of the router

netmask 255.255.255.0

dns-nameservers 127.0.0.1 --------------Note: I also tried 72.30.35.9, 8.8.4.4, 8.8.8.8, and the IP my client gave. Every time I change the IP here. I issue command "sudo service networking restart" But all IPs have the same results: cannot ping www.yahoo.com but positive for 72.30.35.9

 

With this, I can ping IP, like

user@reporter:/etc/network$ ping 72.30.35.9  -------------Note: I try to ping Yahoo IP, works

PING 72.30.35.9 (72.30.35.9) 56(84) bytes of data.

64 bytes from 72.30.35.9: icmp_seq=1 ttl=49 time=25.7 ms

64 bytes from 72.30.35.9: icmp_seq=2 ttl=49 time=25.7 ms

^C

--- 72.30.35.9 ping statistics ---

2 packets transmitted, 2 received, 0% packet loss, time 1001ms

rtt min/avg/max/mdev = 25.704/25.724/25.745/0.161 ms

 

This indicates from server X, I can somehow connecting to outside/internet

 

user@reporter:/etc/network$ ping 8.8.8.8 -------------Note: I try to ping Google IP, does not work

PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data.

^C

--- 8.8.8.8 ping statistics ---

7 packets transmitted, 0 received, 100% packet loss, time 6040ms

 

user@reporter:/etc/network$ ping 8.8.4.4 -------------Note: I try to ping another Google IP, works. Don't know why

PING 8.8.4.4 (8.8.4.4) 56(84) bytes of data.

64 bytes from 8.8.4.4: icmp_seq=1 ttl=50 time=12.8 ms

64 bytes from 8.8.4.4: icmp_seq=2 ttl=50 time=12.7 ms

^C

--- 8.8.4.4 ping statistics ---

2 packets transmitted, 2 received, 0% packet loss, time 1001ms

rtt min/avg/max/mdev = 12.719/12.768/12.817/0.049 ms

 

HOWEVER I CANNOT PING BY DOMAIN NAME

 

user@reporter:/etc/network$ ping www.yahoo.com  -------------Note: I try to ping Yahoo name, does not work. This is the problem

ping: unknown host www.yahoo.com

user@reporter:/etc/network$ ping www.google.com   -------------Note: I try to ping Google name, does not work

ping: unknown host www.google.com

user@reporter:~/Documents/tony/temp$ wget www.yahoo.com -------------Note: this command supposed to be get a index.html file

--2019-05-23 20:29:51--  http://www.yahoo.com/

Resolving www.yahoo.com (www.yahoo.com)... failed: Temporary failure in name resolution.

wget: unable to resolve host address ‘www.yahoo.com’

user@reporter:~/Documents/tony/temp$ wget 8.8.4.4 -------------Note: did not get anything, but output indicating "Connecting"

--2019-05-23 20:30:21--  http://8.8.4.4/

Connecting to 8.8.4.4:80... ^C

 

I know/guess this is more server level question, rather than router level. Just hope if there's a slight possibility it's router setting problem, and also hope someone here may know both router and Ubuntu sys. admin (we're actually willing to pay desired expert to fix the issue and for future/potential problems).

 

Thanks a lot!

-txu

 

Everyone's tags (3)
1 ACCEPTED SOLUTION

Accepted Solutions
VIP Advisor

Re: Can ping IP address but not by domain name. A DNS issue?

Glad it was sorted finally, this could be DNS resolve issue from the device you have mentioned.

 

Any way end it was all fine. can you make this post as a resolved.

BB
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8 REPLIES 8
VIP Advisor

Re: Can ping IP address but not by domain name. A DNS issue?

THIS IS  DUPLICATE POST

 

ping: unknown host www.yahoo.com

 

I see that you have nslookup resolution issue.

 

check your /etc/resolv.conf

 

echo 8.8.8.8 > /etc/resolv.conf

 

type nslookup google.co.uk  <-- this should work 

 

 

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txu Beginner
Beginner

Re: Can ping IP address but not by domain name. A DNS issue?

thanks!
currently it's
nameserver 8.8.4.4
in the /etc/resolv.conf file
no servers could be reached
Beginner

Re: Can ping IP address but not by domain name. A DNS issue?

It seems likely that the client has rules as to what dns servers you are allowed to use. 

But if I understand correctly you have already tried with the dns server that the client provided?

txu Beginner
Beginner

Re: Can ping IP address but not by domain name. A DNS issue?

Yes, I didn't.
txu Beginner
Beginner

Re: Can ping IP address but not by domain name. A DNS issue?

I mean I tried the IP client provided and it didn't work
VIP Advisor

Re: Can ping IP address but not by domain name. A DNS issue?

check any iptables running on Linux 

 

iptables -xnvL 

 

testing flush the iptables and test it

 

iptaables -F

 

BB
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txu Beginner
Beginner

Re: Can ping IP address but not by domain name. A DNS issue?

After a couple of days, I can now ping www.yahoo.com from my server. However how the problem is solved, I have NO IDEA! Probably it takes time to configure the setting? Or my client change some settings at their end......
VIP Advisor

Re: Can ping IP address but not by domain name. A DNS issue?

Glad it was sorted finally, this could be DNS resolve issue from the device you have mentioned.

 

Any way end it was all fine. can you make this post as a resolved.

BB
*** Rate All Helpful Responses ***
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