Zijici IP adresa

[Martin Horak]

> Jan Marek <jmarek na jcu.cz> wrote:
> -> traceroute IMHO pouziva pouze a jenom protokol ICMP a vytvari
> -> paket tak, ze postupne zvysuje polozku TTL v paketu. Tim se mu ->
> paket vraci postupne od vsech routeru na ceste se zpravou ->
> "time-exceeded". Pokud ale tuhle zpravu na routeru zakazete, tak -> se
> paket nevrati...
> 
> pokial viem, na icmp pakety sa reply nesmie posielat:
> 
> rfc792:
> 
>    The ICMP messages typically report errors in the processing of
>    datagrams.  To avoid the infinite regress of messages about
>    messages etc., no ICMP messages are sent about ICMP messages.  Also
>    ICMP messages are only sent about errors in handling fragment zero
>    of fragemented datagrams.  (Fragment zero has the fragment offeset
>    equal zero).
> 
> Existuje sice RFC1939 (Traceroute Using an IP Option) ale je v stadiu
> EXPERIMENTAL ... takze uprimne sa priznam neviem ako presne funguje
> traceroute cez ICMP :(
> 
> Yo a keby ste si precitali doc k traceroute videli by ste ze sa
> pouziva UDP (zrejme presne z tohoto dovodu).
> 
Lidi, ctete manualy. Je tam vsechno.
traceroute -I <host> pouziva misto UDP ICMP ECHO (jako ping). Nekdy 
se to hodi, treba u firewallu - UDP vetsinou zahazuji, PING 
propousteji (nebo alespon odpovidaji).
ICMP ECHO bude tedy asi vyjimka ze zmineneho RFC792.


--
Ing. Martin Horak
SCE a.s. Decin
horakm na mail.sce.cz