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DHCP Dynamic Host Configuration Protocol

DHCP Dynamic Host Configuration Protocol. DHCP koriste hostovi u da bi prilikom podizanja operativnog sistema automatski konfigurisali parametere kao što su IP addresa , subnet maska , default gateway itd . Parametre šalje DHCP server po zahtevu hosta Host je DHCP klijent

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DHCP Dynamic Host Configuration Protocol

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  1. DHCPDynamic Host Configuration Protocol DHCP koristehostovi u da bi prilikompodizanjaoperativnogsistemaautomatskikonfigurisaliparameterekaoštosu IP addresa, subnet maska, default gateway itd. Parametrešalje DHCP server pozahtevuhosta Host je DHCP klijent Komunikacija se odvijaprema “paradigmi” klijent-server

  2. DHCP server je obično glavni (centalni ) server u lokalnoj mreži koji održava administrator mreže • Pošto su podaci na njemu pod kontrolom administratora, DHCP klijenti uvek dobijaju ažurne parametre koji se kontinualno ažuriraju prema aktuelnim potrebama lokalne mreže • Ako postoji više rutera, ruteri se moraju konfigurisati da prosleđuju zahteve DHCP serveru (DHCP Relay Agent feature). • U jednostavnijim mrežama ruter može biti DHCP server

  3. Pošto svaki host treba da ima IP adresu da bi komunicirao preko IP mreže, DHCP smanjuje administratoru posao stalnog statičkog podešavanja parametara svakog pojedinačnog hosta • Na primer ako se host preseli na neku drugu “podmrežu” treba da promeni IP adresu. Sa DHCP-om se konfiguracija obavi automatski, host dobije podatke sa DHCP servera • DHCP je transparentan za dinamičko dodeljivanje adresa, pa samim tim i NAT

  4. Opis protokola • DHCP uses a client-server model where one or more servers (DHCP servers) allocate IP addresses and other optional configuration parameters to clients (hosts) upon client bootup. • These configuration parameters are leased by the server to the client for some specified amount of time. • When a host boots up, the TCP/IP stack in the host transmits a broadcast (DHCPDISCOVER) message in order to gain an IP address and subnet mask, among other configuration parameters. • This initiates an exchange between the DHCP server and the host. During this exchange, the client passes through the several well defined states listed below:

  5. nitializing • Selecting • Requesting • Bound • Renewing • Rebinding

  6. Role of DHCP/BootP Relay Agent • Routers, by default, will not forward broadcast packets. • Since DHCP client messages use the destination IP address of 255.255.255.255 (all Nets Broadcast), DHCP clients will not be able to send requests to a DHCP server on a different subnet unless the DHCP/BootP Relay Agent is configured on the router. • The DHCP/BootP Relay Agent will forward DHCP requests on behalf of a DHCP client to the DHCP server. • The DHCP/BootP Relay Agent will append its own IP address to the source IP address of the DHCP frames going to the DHCP server. • This allows the DHCP server to respond via unicast to the DHCP/BootP Relay Agent. • The DHCP/BootP Relay Agent will also populate the Gateway IP address field with the IP address of the interface on which the DHCP message is received from the client. • The DHCP server uses the Gateway ip address field to determine the subnet from which the DHCPDISCOVER, DHCPREQUEST, or DHCPINFORM message originates.

  7. Otvoriti komandnu liniju rutera (CLI – command line interface). • Ukoliko je ruter u trenutno neaktivnom stanju (komanda linija se završava znakom >, odnosno Router>) potrebno ga je aktivirati komandom enable. Nakon toga komandna linija se završava znakom # odnosno Router#. • Potom je potrebno aktivirati konfiguracioni terminal za podešavanje parametara rutera komandom configuration terminal ili skraćeno conf t nakon čega se početak komandne linije menja u Router(config)#. ip dhcp pool MyPool net 192.168.10.0 255.255.255.0 ip dhcp exclude 192.168.10.1 192.168.10.5 default 192.168.10.1 dns 20.0.0.2

  8. Nakon konfigurisanja DHCP-a potrebno je izaći iz konfiguracionog moda pomoću naredbe exit i aktivirati trenutna podešavanja komandom copy run start. • Ništa ne unositi za ime konfiguracionog fajla (samo pritisnuti Enter). • Trenutna konfiguracija se dobija komandom show run

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