#
# /etc/sysctl.conf - Configuration file for setting system variables
# See /etc/sysctl.d/ for additional system variables.
# See sysctl.conf (5) for information.
#
#kernel.domainname = example.com
# Uncomment the following to stop low-level messages on console
#kernel.printk = 3 4 1 3
##############################################################3
# Functions previously found in netbase
#
# Uncomment the next two lines to enable Spoof protection (reverse-path filter)
# Turn on Source Address Verification in all interfaces to
# prevent some spoofing attacks
#net.ipv4.conf.default.rp_filter=1
#net.ipv4.conf.all.rp_filter=1
# Uncomment the next line to enable TCP/IP SYN cookies
# See http://lwn.net/Articles/277146/
# Note: This may impact IPv6 TCP sessions too
#net.ipv4.tcp_syncookies=1
# Uncomment the next line to enable packet forwarding for IPv4
#net.ipv4.ip_forward=1
# Uncomment the next line to enable packet forwarding for IPv6
# Enabling this option disables Stateless Address Autoconfiguration
# based on Router Advertisements for this host
#net.ipv6.conf.all.forwarding=1
###################################################################
# Additional settings - these settings can improve the network
# security of the host and prevent against some network attacks
# including spoofing attacks and man in the middle attacks through
# redirection. Some network environments, however, require that these
# settings are disabled so review and enable them as needed.
#
# Do not accept ICMP redirects (prevent MITM attacks)
#net.ipv4.conf.all.accept_redirects = 0
#net.ipv6.conf.all.accept_redirects = 0
# _or_
# Accept ICMP redirects only for gateways listed in our default
# gateway list (enabled by default)
# net.ipv4.conf.all.secure_redirects = 1
#
# Do not send ICMP redirects (we are not a router)
#net.ipv4.conf.all.send_redirects = 0
#
# Do not accept IP source route packets (we are not a router)
#net.ipv4.conf.all.accept_source_route = 0
#net.ipv6.conf.all.accept_source_route = 0
#
# Log Martian Packets
#net.ipv4.conf.all.log_martians = 1
#
# Disable IPv6
net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1
ping -c4 http://www.google.it
PING http://www.google.it (216.58.198.3) 56(84) bytes of data.
64 bytes from mil04s03-in-f3.1e100.net (216.58.198.3): icmp_seq=1 ttl=54 time=30.9 ms
64 bytes from mil04s03-in-f3.1e100.net (216.58.198.3): icmp_seq=2 ttl=54 time=18.0 ms
64 bytes from mil04s03-in-f3.1e100.net (216.58.198.3): icmp_seq=3 ttl=54 time=16.5 ms
64 bytes from mil04s03-in-f3.1e100.net (216.58.198.3): icmp_seq=4 ttl=54 time=16.7 ms
--- http://www.google.it ping statistics --- 4 packets transmitted, 4 received, 0% packet loss, time 3003ms
rtt min/avg/max/mdev = 16.591/20.561/30.901/5.998 ms
Il ping ha avuto successo, non ci sono errori di pacchetti perduti.
Un altro controllo che puoi fare è andare su Firefox: Modifica > Preferenze > Avanzate > Rete > Impostazioni; controlla che sia impostato su Nessun proxy, altrimenti lo correggi e poi clicca in basso a destra su OK.
Potrebbe essere un problema di DNS nel file /etc/resolv.conf.