How to disable ipv6 in Debian

Here are simple steps to disable ipv6 in Debian:

  1. Comment out anything related to ipv6 in /etc/hosts
  2. SSH. Ensure AddressFamily inet is set in/etc/ssh/sshd_config. Restart ssh.
  3. BIND. Ensure listen-on-v6 { none; }; in/etc/bind/named.conf.options. Restart bind9.
  4. NTP. Ensure -4 option is set in /etc/default/ntp (e.g. NTPD_OPTS=’-4 -g’). Restart ntp.
  5. APACHE2. Ensure Listen 0.0.0.0:80 in/etc/apache2/ports.conf file. Restart apache2.
  6. RPCBIND (rpc.statd, rpc.mountd). Comment out the appropriate entries in /etc/netconfig:
    udp        tpi_clts      v     inet     udp     - -
    tcp        tpi_cots_ord  v     inet     tcp     - -
    #udp6       tpi_clts      v     inet6    udp    - -
    #tcp6       tpi_cots_ord  v     inet6    tcp    - -
    rawip      tpi_raw       -     inet      -      - -
    local      tpi_cots_ord  -     loopback  -      - -
    unix       tpi_cots_ord  -     loopback  -      - -
    
  7. PostgreSQL 9. Ensure ipv4 in listen_addresses (file/etc/postgresql/9.1/main/postgresql.conf):
    # - Connection Settings
    listen_addresses = '0.0.0.0'
    

    Comment out lines related to ipv6 (file/etc/postgresql/9.1/main/pg_hba.conf):

    # IPv6 local connections:
    #host  all     all     ::1/128   md5
    

    Restart postgresql.

  8. Disable ipv6 in kernel:
    echo net.ipv6.conf.all.disable_ipv6=1 \
    > /etc/sysctl.d/disableipv6.conf
    
  9. Disable ipv6 in kernel modules (file/etc/modprobe.d/aliases.conf):
    # alias net-pf-10 ipv6
    alias net-pf-10 off
    alias ipv6 off
    

The next time the system boots it will have ipv6 disabled. Let verify it with:

netstat -tunlp

Here is a sample output:

Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address   State    PID/Program name
tcp        0      0 192.168.10.2:53         0.0.0.0:*         LISTEN      895/named       
tcp        0      0 127.0.0.1:53            0.0.0.0:*         LISTEN      895/named       
tcp        0      0 0.0.0.0:22              0.0.0.0:*         LISTEN      734/sshd        
tcp        0      0 127.0.0.1:953           0.0.0.0:*         LISTEN      895/named       
udp        0      0 192.168.10.2:53         0.0.0.0:*                     895/named       
udp        0      0 127.0.0.1:53            0.0.0.0:*                     895/named         

Read more about ipv6 here

Mind Reference: How to disable ipv6 in Debian.

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