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I am not so into networking and systems engineering.

I have an Ubuntu 18.04 VM that is in a network of a client that is

1) Unable to perform ping of addresses external to the network (but I can ping other machine inside this network so ping is working).

This is what I am obtaining:

andrea.nobili@VHPLWSO2EI01:~$ ping 8.8.8.8
PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data.

--- 8.8.8.8 ping statistics ---
111 packets transmitted, 0 received, 100% packet loss, time 112647ms

2) I can't resolve address using DNS:

Trying to resolve google.com I am obtaining this error:

andrea.nobili@VHPLWSO2EI01:~$ nslookup
> google.com
;; Got SERVFAIL reply from 127.0.0.53, trying next server
Server:         10.144.8.8
Address:        10.144.8.8#53

** server can't find google.com: SERVFAIL

But the strange thing that I am not understanding is that if I use wget I can download google.com page (so wget seems to correctly resolve google.com address):

wget google.com
--2019-12-06 12:51:04--  http://google.com/
Connecting to 10.173.21.241:3128... connected.
Proxy request sent, awaiting response... 301 Moved Permanently
Location: http://www.google.com/ [following]
--2019-12-06 12:51:04--  http://www.google.com/
Connecting to 10.173.21.241:3128... connected.
Proxy request sent, awaiting response... 200 OK
Length: unspecified [text/html]
Saving to: ‘index.html.11’

index.html.11                           [ <=>                                                                ]  11.72K  --.-KB/s    in 0.009s

2019-12-06 12:51:04 (1.24 MB/s) - ‘index.html.11’ saved [11999]

An other additional information is: there is a proxy. On this machine I installed CNTLM proxy. This local proxy perform the authentication on a Windows system to navigate on Internet. Then I export http_proxy and https_proxy to point to this local proxy:

export http_proxy=http://USWRNAME:PASSWORD@IP_OF_MACHINE:3128
export https_proxy=https://USWRNAME:PASSWORD@IP_OF_MACHINE:3128
export HTTP_PROXY=http://USWRNAME:PASSWORD@IP_OF_MACHINE:3128
export HTTPS_PROXY=https://USWRNAME:PASSWORD@IP_OF_MACHINE:3128

The proxy works fine. If I doesn't set the proxy I can't use wget.

So I have the following doubts:

1) Can be the ping problem related to the DNS problem?

2) Why nslookup can't resolve the IP address of google.com but wget seems to be able to do it?

3) Could be something not strictly related to this Linux machine but something related to the network? I mean something related to the router configuration, the DNS or something related to the firewall?

4) In case how could be something related to the firewall? From what I know the firewall is related to the ports (filter ports) but ping should be on ICMP and doesn't know port concept

What could be the causes of these two problems? How can I investigate better or what can I ask to the system engineer of the client?

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  • 2
    Web browser just contact the proxy (which is usually a local server) and leave all the name resolution to it. You can be blocked by firewall rules, and maybe the proxy is not blocked. In fact, that is an usual approach on some private networks: leave access to the Internet to just a few authorized hosts (like a proxy).
    – Roberto Paz
    Commented Dec 6, 2019 at 12:26

2 Answers 2

Reset to default
1

What you describe is consistent with an incorrect default gateway.

The output of command netstat -nr should show the configured default route.

The route command is also useful for discovering detail about routing problems.

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  • indeed, specifying a gateway in my /etc/network/interfaces file allowed me to reach external IPs
    – Cheetaiean
    Commented Feb 21, 2023 at 22:43
1

You need to enable "Replicate physical network connection state" in Vmware network's bridge mode:

1

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