Network test

local network

outgoing ip

• ipv4:

ip -4 --oneline route get 1 | grep -oP '(?<=src\s)\d+(\.\d+){3}'

• ipv6:

ip -6 --oneline route get 1:: | grep -oP '(?<=src\s)[\da-f:]+'

host ip of specific network

• ipv4:

LOCAL_NETWORK=10.0.0.0/24
ip -4 --oneline address show to ${LOCAL_NETWORK} | grep -oP '(?<=inet\s)\d+(\.\d+){3}'

• ipv6:

LOCAL_NETWORK=fc00::/7
ip -6 --oneline address show sto ${LOCAL_NETWORK} | grep -oP '(?<=inet\s)[\da-f:]+'

dns

name server resolver from specific dns

nslookup campisano.org 8.8.4.4

open ports

netstat -tulpn
# OR
ss -tulpn

network traffic

e.g. inbound from specified interface and excluding specified ports:

tcpdump -n -i eth0 host 187.126.64.20 and not tcp port 22 and not tcp port 80

network access

ping campisano.org

routing

traceroute -M tcp -N 100 -m 100 campisano.org

specific port access

telnet campisano.org 80
# or
nc -vv -w 3 -z campisano.org 80

homemade telnet

In some basic system like cloud minimal virtual machines, there are no network utilities like telnet, so there are some alternatives:

• bash command:

#!/usr/bin/env bash

# from http://rednafi.com/misc/http-requests-via-dev-tcp/

set -o errtrace -o pipefail

HOST=$1
PORT=$2
TEXT=$3

if test "$#" -ne 3
then
    echo "Usage:   "`basename $0`" <host> <port> <text>"
    echo "Example: "`basename $0`" www.campisano.org 80 \"GET /wiki/Main HTTP/1.0\r\nHost: www.campisano.org\r\nConnection: close\r\n\r\n\""
    exit 0
fi

# Open a TCP connection to example.com on port 80 and assign file descriptor 3
# The exec command keeps /dev/fd/3 open throughout the lifetime of the script
# 3<> enables bidirectional read-write
exec 3<>/dev/tcp/${HOST}/${PORT}

# Send the HTTP GET request to the server
# >& redirects stdout to /dev/fd/3
echo -e "${TEXT}" >&3

# Read and print the server's response
# <& redirects the output of /dev/fd/3 to cat
cat <&3

# Close the file descriptor, terminating the TCP connection
exec 3>&-

• perl script implementation (using vanilla Socket package):

#!/usr/bin/env perl

# from https://www.oreilly.com/openbook/webclient/ch04.html

use Socket;

$|=1; # autoflush

sub open_TCP
{
  # get parameters
  my ($FS, $dest, $port) = @_;

  my $proto = getprotobyname('tcp');
  socket($FS, PF_INET, SOCK_STREAM, $proto);
  my $sin = sockaddr_in($port,inet_aton($dest));
  connect($FS,$sin) || return undef;

  my $old_fh = select($FS);
  $| = 1; 		        # don't buffer output
  select($old_fh);
  1;
}


# If no parameters were given, print out help text
$num_args = $#ARGV + 1;
if ($num_args != 3) {
    print "Usage: telnet.pl <host> <port> <text>\n";
    print "Example: telnet.pl www.campisano.org 80 \$'GET /wiki/Main HTTP/1.0\\r\\nHost: www.campisano.org\\r\\n\\r\\n'\n";
    exit(-1);
}

$host=$ARGV[0];
$port=$ARGV[1];
$text=$ARGV[2];

# contact the server
print "connecting $host:port ...\n";

if (open_TCP(F, $host, $port) == undef) {
  print "Error connecting to server at $ARGV[0]\n";
  exit(-2);
}

# send the GET method with / as a parameter
print "sending $text ...\n";
print F "$text";

# print out the response
print "printing response ... \n";
print $_ while (<F>);

close(F);

java specific ipv6 network behaviour

from https://docs.oracle.com/javase/8/docs/technotes/guides/io/example/Ping.java

• compile a simple ping app

curl -O https://docs.oracle.com/javase/8/docs/technotes/guides/io/example/Ping.java
javac Ping

• from host with both ipv4 and ipv6 networks

java -Djava.net.preferIPv4Stack=true -Djava.net.preferIPv6Addresses=false Ping 80 HOSTNAME
HOSTNAME/IPV4:80 : TIMEms
java -Djava.net.preferIPv4Stack=true -Djava.net.preferIPv6Addresses=true Ping 80 HOSTNAME
HOSTNAME/IPV4:80 : TIMEms
java -Djava.net.preferIPv4Stack=false -Djava.net.preferIPv6Addresses=true Ping 80 HOSTNAME
HOSTNAME/IPV6:80 : TIMEms
java -Djava.net.preferIPv4Stack=false -Djava.net.preferIPv6Addresses=false Ping 80 HOSTNAME
HOSTNAME/IPV4:80 : TIMEms
java Ping 80 HOSTNAME
HOSTNAME/IPV4:80 : TIMEms

• from host with only ipv6 network

java -Djava.net.preferIPv4Stack=true -Djava.net.preferIPv6Addresses=false Ping 80 HOSTNAME
HOSTNAME/IPV4:80 : java.net.SocketException: Network is unreachable
java -Djava.net.preferIPv4Stack=true -Djava.net.preferIPv6Addresses=true Ping 80 HOSTNAME
HOSTNAME/IPV4:80 : java.net.SocketException: Network is unreachable
java -Djava.net.preferIPv4Stack=false -Djava.net.preferIPv6Addresses=true Ping 80 HOSTNAME
HOSTNAME/IPV6:80 : TIMEms
java -Djava.net.preferIPv4Stack=false -Djava.net.preferIPv6Addresses=false Ping 80 HOSTNAME
HOSTNAME/IPV4:80 : java.net.SocketException: Network is unreachable
java Ping 80 HOSTNAME
HOSTNAME/IPV4:80 : Timed out