  DNS connectivity checking


  Name resolution (getting an IP number from a hostname) and reverse
  mapping (getting a hostname from an IP number) are at the heart of
  _T_C_P_/_I_P networking. A broken or erratic _D_N_S is often the cause of most
  network problems and sometimes poor performance.

  11..  IItt''ss ssllooww bbuutt iitt wwoorrkkss!!

  _T_C_P_/_I_P was designed to operate over wide area networks as well a
  smaller ones. On large networks, you may from time to time encounter
  long delays. This is a normal (often annoying) condition and the _I_P
  protocols are ready to cope with this. A bad DNS or broken network
  connection making the DNS unreachable will cause all kinds of delays
  (several seconds). Fortunately, quite often a backup facility exists
  (i.e. a second DNS) and after some timeout, the system becomes active.

  Unfortunately, this often hides the real problem and slow speed is
  ttributed to the wrong reason. It may be attributed to an overloaded
  _I_n_t_e_r_n_e_t, or to an _I_S_P over-selling bandwidth.


  22..  TThhee ssttrraatteeggyy

  _L_i_n_u_x_c_o_n_f makes a small check with the _D_N_S before trying to further
  configure the machine. It probes the _D_N_S and waits for four seconds.
  It then reports an error if the _D_N_S has failed to answer within this
  period. Here are different techniques to support this strategy:


  +o  You should have good network connectivity with your _D_N_S.  The DNS
     may be either located on the local Ethernet network, or right on
     the other side of a _P_P_P link.

  +o  If no DNS is available near your network, it is better to setup a
     caching DNS on your machine. Linuxconf does this automatically when
     you create a DNS with it.

  +o  _D_N_S problems are probably the most difficult problems to track or
     identify for new users. Try to detect any problems quickly.  item>_A
     _D_N_S does not fail often. When something is wrong with the DNS, the
     effect is so pervasive, however, that a user may believe his
     machine is either hung or broken.


  33..  TThhee qquueerryy

  _L_i_n_u_x_c_o_n_f sends the following query to the DNS:


               nslookup -q=soa 0.0.127.in-addr.arpa


  All properly configured DNS servers should answer this request. It is
  possible for a working DNS to operate without a reverse mapping for
  the network 127.0.0. This is a flaw and should be corrected.  (Run
  linuxconf on this machine and configure the DNS with it and Linuxconf
  will silently fix this.)


  44..  TToo qquueerryy oorr nnoott


  Some machines may lack DNS connectivity simply because there is no DNS
  in the organization. Linuxconf won't probe the DNS if there is no name
  server specified in /etc/resolv.conf.

  You can also disable this behavior altogether. Just go into the
  networking submenu and pick the Name server specification (DNS) entry.
  A checkbox allows you to disable this. This is the only purpose of the
  checkbox in this dialog.