Newsgroup: it.comp.aiuto
Titolo: Comee si legge PING

Qualcuno (in E-mail cosě non carichiamo l'area) potrebbe spiegarmi che
dati fornisce come risposta PING e i parametri medi che indicano che
la connessione funziona bene?
Se poi mi indicate una bella FAQ non rompo piů le scatole  con domande
da RTFM. ;-)))
Pinging 134.187.120.2  with 32 bytes of data:
Reply from 
134.187.120.2
: bytes=32 time=73ms TTL=255
Reply from 
134.187.120.2
: bytes=32 time=74ms TTL=255
Reply from 
134.187.120.2
: bytes=32 time=74ms TTL=255
Reply from 
134.187.120.2
: bytes=32 time=74ms TTL=255
Significa che il server trasmette a me 32 bytes ogni 73 millisecondi?
che cos'č allora il TTL=255
Enrico Giubertoni                       E-Mail 
rs...@intercom.it
  Birthdays are good for you ...
  A federally funded study has shown that people with the most birthdays
  live the longest ;-))))))

 che cos'è allora il TTL=255
Ping trasmette per  default un pacchetto datagram  "ICMP ECHO_REQUEST"
forzare  un host   o    un    gateway a   ritrasmenttere un      "ICMP
ECHO_RESPONSE". I 73 millisecondi  sono il tempo trascorso tra l'invio
della  richiesta e la ricezione della  risposta o altrimenti, il tempo
necessario   per   percorrere  il   circuito  andata-e-ritorno  (round
trip).  Il pacchetto "ICMP  ECHO_REQUEST"  e` detto 'ping' in analogia
con gli impulsi sonar, ed ha lunghezza variabile a scelta del mittente
(di solito e' 64, ma puo' essere meno).
TTL e' l'acronimo  per Time To Live (grazie  mau!),  che' piu' che  un
tempo rappresenta  il numero  di   router  IP che  il pacchetto   puo'
attraversare prima di essere  scartato, ed  assomiglia quindi piu'  ad
una gittata.
Qui  di  seguito un   paio di  estratti (in   inglese) dell'output del
comando "man ping" del SunOS4.1.3_U1 e di Linux:
DESCRIPTION
     ping utilizes the  ICMP  protocol's  mandatory  ECHO_REQUEST
     datagram  to elicit an ICMP ECHO_RESPONSE from the specified
     host ,  or  network  gateway.   ECHO_REQUEST  datagrams,  or
     "pings,"   have  an  IP  and  ICMP  header,  followed  by  a
     structtimeval, and then an arbitrary number of bytes to  pad
     out  the  packet.  If host responds, ping will print host is
     alive on the standard  output  and  exit.   Otherwise  after
     timeout  seconds,  it  will  write no answer from host.  The
     default value of timeout is 20 seconds.
TTL DETAILS
     The TTL value of an IP packet represents the maximum number of IP routers
     that the packet can go through before being thrown away.  In current
     practice you can expect each router in the Internet to decrement the TTL
     field by exactly one.
     The TCP/IP specification states that the TTL field for TCP packets should
     be set to 60, but many systems use smaller values (4.3 BSD uses 30, 4.2
     used 15).
     The maximum possible value of this field is 255, and most Unix systems
     set the TTL field of ICMP ECHO_REQUEST packets to 255.  This is why you
     will find you can ``ping'' some hosts, but not reach them with telnet(1)
     or ftp(1).
     In normal operation ping prints the ttl value from the packet it re-
     ceives.  When a remote system receives a ping packet, it can do one of
     three things with the TTL field in its response:
     o   Not change it; this is what Berkeley Unix systems did before the
         4.3BSD-Tahoe release.  In this case the TTL value in the received
         packet will be 255 minus the number of routers in the round-trip
         path.
     o   Set it to 255; this is what current Berkeley Unix systems do.  In
         this case the TTL value in the received packet will be 255 minus the
         number of routers in the path from the remote system to the pinging
         host.
     o   Set it to some other value.  Some machines use the same value for
         ICMP packets that they use for TCP packets, for example either 30 or
         60.  Others may use completely wild values.
o   oooooo	Gian Uberto Lauri
      o    o	
sa...@maya.dei.unipd.it
     o o