Prin proxwrisoyme sthn apolaysh ths ypodiktuwshs (sub-networking) , xreiazetai na 8esoyme ta basika sxetika me tis IP diey8unseis.
Prwta ap'ola, as jeka8arisoyme merikes basikes aities parejhghshs - oi ari8moi IP einai den anati8entai se hosts. Oi ari8moi IP anati8entai se interfaces diktuwn poy exoyn oi hosts.
Eeee - Ti einai ayto?
Enw polloi (ean oxi oi perissoteroi) ypologistes se ena IP diktyo 8a katexoyn ena mono interface diktuoy (kai exoyn ena mono ari8mo IP san synepeia), aytos den einai o monos tropos poy ginontai ta pragmata. Oi ypologistes ka8ws kai alles syskeyes mporoun na exoyn diafora (ean oxi polla) interfaces diktuoy- kai ka8e interface na exei ton diko toy ari8mo IP.
Etsi mia syskeyh me 6 diaforetika interfaces (opws enas dromologhths - router) 8a exei 6 IP ari8mous - enan gia ka8e interface gia ka8e diktyo sto opoio einai syndedemenos. H aitia gi'ayto einai profanhs otan koitajoyme ena diktyo IP!
Prol'ayta, oi perissoteroi anaferontai se host diey8unseis otan anaferontai se ari8mous IP. Apla na 8ymaste, ayto einai mia eykolia gia ton ari8mo IP toy sygkekrimenoy interface se ayton ton host. Polles (ean oxi oi pleiochfia) twn syskeywn sto Internet exoyn monadiko interface kai epomenws monadiko ari8mo IP.
Sthn sygkekrimenh (IPv4) ylopoihsh twn ari8mwn IP, aytoi apotelountai apo 4 (8 bit) bytes - dinontas ena sunolo 32 bits dia8esimhs plhroforias. Ayto katalhgei se ari8mous poy einai mallon megaloi (akoma kai otan einai grammenoi se dekadikh morfh). Etsi gia anagnwsimothta (ka8ws kai gia logoys organwshs) oi ari8moi IP einai synh8ws grammenoi se morfh 'tetradas me teleies' ('dotted quad'). O IP ari8mos
192.168.1.24
einai ena paradeigma aytou- 4 (dekadikoi) ari8moi diaxorizomenoi apo (.) teleies.
Ka8ws ka8e enas apo toys 4 ari8mous einai h dekadikh anaparastash enos 8 bit byte, ka8e enas apo toys 4 ari8mous mporei na einai apo 0 ews 255 (dhladh 256 monadikes times - 8ymh8hte, to 0 einai kai ayto mia timh).
Epipleon, meros toy ari8mou IP enos host prosdiorizei to diktyo sto opoio o host edreuei, ta ypoloipa 'bits' toy ari8mou IP prsdiorizoyn to idio to host (oyps... -to interface toy diktuoy). Akribws to posa bits xrhsimopoiountai to ID toy diktuoy kai posa einai dia8esima gia na prosdiorizoyn hosts (interfaces) se ayto to diktyo orizetai apo thn 'klash' ('class') toy diktuoy.
Yparxoyn treis klaseis ari8mwn IP
Anakefalaiwsh:
Tajh diktuoy Xrhsimo euros timwn toy 1oy byte (dekadiko)
A (1h) 1 to 126
B (2h) 128 to 191
C (3h) 192 to 254
Yparxoyn epishs eidikes diey8unseis poy einai desmeymenes gia 'mh syndedemena' diktya - ayta einai diktya poy xrhsimopoioun IP alla den einai syndedemena sto Internet, oi diey8unseis aytes einai:-
8a parathrhsete oti to keimeno ayto xrhsimopoiei aytes tis allhloyxies diey8unsewn gia na apofeyx8ei to mperdema me 'pragmatika' diktya kai hosts.
Oi ari8moi IP mporei na exoyn treis pi8anes shmasies:-
Gia anakefalaiwsh kai gia na jeka8arisoyme ta pragmata
Gia ena diktyo klashs A ...
(ena byte toy xwroy dieu8ynshs toy diktuoy akoloy8oumeno apo tria
bytes toy xwroy dieu8ynshs toy host)
10.0.0.0 einai enas ari8mos, diktuoy klashs A giati ola ta host
bits toy xwroy dieu8ynshs, einai 0
10.0.1.0 einai h dieu8hynsh enos host se ayto to diktyo
10.255.255.255.255 einai h dieu8ynsh anakoinwshs/ekpomphs (broadcast) aytou toy diktuoy
giati ola ta host bits toy xwroy dieu8ynshs einai 1
Gia ena diktyo klashs B ...
(duo bytes toy xwroy dieu8ynshs diktuoy akoloy8oumena apo duo bytes toy
xwroy dieu8ynshs toy host)
172.17.0.0 einai enas ari8mos diktuoy klashs B
172.17.0.1 einai h dieu8ynsh enos host se ayto to diktyo
172.17.255.255 einai h dieu8ynsh anakoinwshs/ekpomphs aytou toy diktuoy
Gia ena diktyo klashs C...
(tria bytes xwros dieu8ynshs diktuoy akoloy8oumenos apo ena byte toy
xwroy dieu8ynshs toy host)
192.168.3.0 einai enas ari8mos diktuoy klashs C
192.168.3.42 einai h dieu8ynsh enos host se ayto to diktyo
192.168.3.255 einai h dieu8ynsh ekpomphs/anakoinwshs aytou toy diktuoy
sxedon oloi oi IP ari8moi diktuoy poy paramenoyn dia8esimoi gia desmeysh pros to paron einai diey8unseis klashs C.
H maska diktuoy legetai swstotera maska ypodiktuoy (subnetwork mask). Omws, genika anaferomaste s'ayth ws h maska diktuoy.
H maska diktuoy kai oi epiptwseis ths sthn metafrash twn IP diey8unsewn, topika, se ena kommati IP diktuoy poy kyriws mas afora edw, ka8ws ayto ka8orizei poia (ean yparxei kapoia) ypo-diktuwsh lambanei xwra.
H klassikh maska (upo-) diktuoy einai ola ta bits toy diktuoy mias dieu8ynshs '1' kai ola ta host bits '0'. Ayto shmainei oti oi klassikes maskes diktuoy gia tis treis klaseis diktuwn einai:-
Yparxoyn duo shmantika pragmata poy prepei na 8ymatai kaneis gia thn maska diktuoy:-