Dhcp

Dhcp

• 1.
  DHCP (Dynamic HostConfiguration Protocol) Hc/Ro. Tapan Kumar Khilar
• 2.
  DHCP - Introduction DHCP was created by the Dynamic Host Configuration Working Group of the Internet Engineering Task Force(IETF)  Runs over UDP  Utilizing ports:  67 – connections to server  68 – connections to client  Extension of BOOTP (protocol used for simple interaction)- DHCP enhances the capabilities of BOOTP  DHCP is basically used for dynamic configuration  Uses client–server model
• 3.
  Objective of DHCP DHCP temporarily binds IP address & other configuration parameters to DHCP client & provides framework for passing configuration information to hosts  DHCP was designed to provide computers with temporary address  DHCP is well adapted to situation where hosts move from one location to another or are routinely connected and disconnected  Thus DHCP is mainly used to simplify the installation & maintenance of networked computers.
• 4.
  Characteristics  Centralized IPaddress administration  Backward compatible with BOOTP – therefore a host running the BOOTP client software can request a static configuration from a DHCP server  Supports multiple servers  Provides dynamic assignment  Allows static assignment  DoesŶ’t iŶteract ǁith doŵaiŶ Ŷaŵe serǀice (DNS)
• 5.
   Clients shouldrequire no manual configuration by the user to connect to the network. ◦ Each client should be able to discover appropriate configuration information dynamically. RD-CSY2001-2008/09  IP address, DNS servers, WINS servers, etc.  This is normally accomplished through the use of a Dynamic Host Configuration Protocol ◦ Uses UDP ◦ Ports 67 and 68
• 6.
   DHCP ◦ Requireslittle or no administrative overhead, after initial configurations of the DHCP server. ◦ Dynamically maps IP addresses to MAC addresses. ◦ Addresses can be leased for a predefined amount of time before the lease expires and must be renewed by the client. ◦ Allows 30 configuration parameters. RD-CSY2001-2008/09
• 7.
  Client IP: ?? Gateway:?? DNS: ?? Client IP: 192.168.1.10/24 Gateway: 192.168.1.1 DNS: 192.168.1.6 DHCPDISCOVER Broadcast for a DHCP Server Pool: 192.168.1.0/24 Gateway: 192.168.1.1 DNS Server: 192.168.1.6 DHCPOFFER MAC unicast with configuration information DHCPREQUEST Broadcast requesting configuration information sent in DHCPOFFER DHCPACK Acknowledge configuration information and begins lease RD-CSY2001-2008/09
• 8.
   DHCP operatesin a Client/Server environment and uses the following messages   RD-CSY2001-2008/09 DHCPDISCOVER : Client request for server DHCPOFFER: DHCP server replies to client with configuration information DHCPREQUEST: Client requests the use of configuration information from one of the DHCP servers that sent an offer   DHCPNAK ◦ DHCP server declines Client request to use configuration information ◦ DHCPACK: ◦ from DHCP server acknowledges that Client can now begin to use configuration information DHCPRELEASE ◦ Client requests a release of its DHCP configuration 
• 9.
   A Ciscorouter can be configured as a DHCP server. ◦ Cisco calls this IOS feature “Easy IP” ◦ This feature is helpful for small, remote LANs such as home offices with only one router and a few clients. ◦ In a large, campus network, you would not want to use a router as a DHCP server. RD-CSY2001-2008/09
• 10.
  1. Configure anamed DHCP pool 2. Configure network/subnet mask pool RD-CSY2001-2008/09 3. Configure the default gateway 4. Configure addresses to exclude from the DHCP address pool 5. Configure other needed information ◦ Such as DNS server, Domain Name, NetBIOS Server
• 11.
   Like NAT,a DHCP pool must be named before you can enter DHCP configuration mode. ◦ The argument name identifies the DHCP pool in the running configuration and distinguishes this pool from other pools.  More than one DHCP pool can be defined on a router. RD-CSY2001-2008/09 Router(config)#ip dhcp pool name
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   The net_addressdefines a network or subnet that will be used as a pool of addresses to assign IP address to clients. ◦ You must also define the subnet mask. RD-CSY2001-2008/09 Router(dhcp-config)#network net_address subnet_mask
• 13.
   The ip_addressis the address of the default gateway clients will use to send packets destined for remote networks. ◦ In a simple Easy IP configuration, this is the IP address of the interface that is directly connected to the LAN with clients needing DHCP service. RD-CSY2001-2008/09  You also need to exclude this IP address in the ip excluded-address command. dhcp Router(dhcp-config)#default-router ip_address
• 14.
   The address(es)configured with this command will not be assigned by Easy IP to clients. ◦ The argument address_1 is a single IP address that will be excluded. ◦ If configured, the address_n optional argument defines a range of excluded IP addresses between and including argument_1 to argument_n. RD-CSY2001-2008/09 Router(config)#ip dhcp excluded-address address_1 [address_n]
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  Router(dhcp-config)#dns-server ip_address Router(dhcp-config)#netbios-name-server ip_address Router(dhcp-config)#domain-name name RD-CSY2001-2008/09
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  RTA(config)#ip dhcp excluded-address10.1.1.1 RTA(config)#ip dhcp pool RTA_LAN 10.1.1.0 255.255.255.0RTA(dhcp- config)#networkRTA(dhcp-config)#default-router 10.1.1.1 RD-CSY2001-2008/09
• 17.
   Routers normallyblock all broadcasts, including a broadcasted DHCP message. ◦ If the router is not the DHCP server, you must configure the router to forward the DHCP messages to a dhcp_server_ip. RD-CSY2001-2008/09 Router(config)#ip helper-address dhcp_server_ip
• 18.
   The iphelper- address command configures the router to forward eight UDP services: ◦ Time ◦ TACACS ◦ DNS ◦ BOOTP/DHCP Server ◦ BOOTP/DHCP Client ◦ TFTP ◦ NetBIOS Name Service ◦ NetBIOS datagram Service RTA(config)#ip helper-address 10.2.2.5 RD-CSY2001-2008/09
• 19.
   RD-CSY2001-2008/09 Use the followingcommands to verify and troubleshoot your DHCP configuration: ◦ show running-config  view the DHCP configuration ◦ show ip dhcp binding  displays IP to MAC address bindings and lease expiration date and time ◦ show ip dhcp server statistics  displays a count of the number and type of DHCP messages sent and received ◦ debug ip dhcp server events  watch interactions between the DHCP server and clients