ftp question

[Tsakiris Yannis]

On Thu, 18 Dec 1997, Sifalakis Manolis (WILLY) wrote:
>  Sto polous servers exeis tin dynatotita na tous oriseis rita na
> xrisimopoioun kapoio allo port apo to default .... Alla stin
> default leitourgeia to ftpd xrisimopoiei sigoura ta ports 21(control)
> kai 20(data). Pithanon na se mperdeyei to gegonos oti to connection
> apo (!!) to port 20 to 3ekinaei panta (ane3artita apo tin kateythinsi 
> tis pliroforias), o server ... pros ena "tyxaio" port tou client. Diladi
> to prwto tcp SYN paketo gia to establishment tou connection gia ta data
> to stelnei o server apo to port 20.
> 
> 			Manolis. 

de katalaba kai polla ap'afta pou mou eipes alla oriste ti kanw egw
kai *doulevei* :
afou exw mpei sto server kanonika sto port 21 , otan 8elisw na kanw
kapoio LIST n' kapoio RETR n' kapoio STOR , lew prwta sto server
PORT a,b,c,d,e,f (opou a.b.c.d einai n IP mou kai e*0x100+f ena port
sto opoio exw balei ena listening socket kai perimenw to server na 
me kalesei ekei). meta afou dwsw tin entoli gia apostoli n' lipsi 
dedomenwn o server kanei connect ekei.. (fysika e*0x100+f != 20) .
to allo pou mporw na kanw (an o ypologisths pou de mporei na akouei
se kapio port, p.x. an exw slirp syndesi) einai na pw sto server PASV
kai tote aftos pou leei ok kai mou epistrefei pali ta a,b,c,d,e,f
mono pou afth th fora a.b.c.d einai IP tou server kai e*0x100+f to
port sto opoio 8a prepei na ton kalesw kai apo ti dikh mou empiria
einai panta != 20 . fysika mporei na sou leei na synde8eis sto port
20 , egw bebaia den to exw dei afto pote , kai eksalou mou fenete kai
ligo pontio giati an dexete polles data connections sixronws (apo diafora
clients) 8a yparxei mperdema (poios einai aftos twra..klp) .
Perimenw apopseis...

--Yannis T.

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