Dynamic Host Configuration Protocol - wikipedia Dynamic Host Configuration Protocol `` DHCP '' redirects here. For other uses, see DHCP ( disambiguation ). Not to be confused with HDCP. This article has multiple issues. Please help improve it or discuss these issues on the talk page. ( Learn how and when to remove these template messages ) This article 's lead section does not adequately summarize key points of its contents. Please consider expanding the lead to provide an accessible overview of all important aspects of the article. Please discuss this issue on the article 's talk page. ( November 2015 ) This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. ( April 2014 ) Internet protocol suite Application layer BGP DHCP DNS FTP HTTP IMAP LDAP MGCP MQTT NNTP NTP POP ONC / RPC RTP RTSP RIP SIP SMTP SNMP SSH Telnet TLS / SSL XMPP more... Transport layer TCP UDP DCCP SCTP RSVP more... Internet layer IP IPv4 IPv6 ICMP ICMPv6 ECN IGMP IPsec more... Link layer ARP NDP OSPF Tunnels L2TP PPP MAC Ethernet DSL ISDN FDDI more... The Dynamic Host Configuration Protocol ( DHCP ) is a network management protocol used on TCP / IP networks whereby a DHCP server dynamically assigns an IP address and other network configuration parameters to each device on a network so they can communicate with other IP networks. A DHCP server enables computers to request IP addresses and networking parameters automatically from the Internet service provider ( ISP ), reducing the need for a network administrator or a user to manually assign IP addresses to all network devices. In the absence of a DHCP server, a computer or other device on the network needs to be manually assigned an IP address. DHCP can be implemented on networks ranging in size from home networks to large campus networks and regional Internet service provider networks. A router or a residential gateway can be enabled to act as a DHCP server. Most residential network routers receive a globally unique IP address within the ISP network. Within a local network, a DHCP server assigns a local IP address to each device connected to the network. Contents 1 Overview 2 Operation 2.1 DHCP discovery 2.2 DHCP offer 2.3 DHCP request 2.4 DHCP acknowledgement 2.5 DHCP information 2.6 DHCP releasing 3 Client configuration parameters 4 DHCP options 4.1 Documented in RFC 2132 4.1. 1 DHCP client vendor identification 4.2 Documented Elsewhere 4.2. 1 Relay Agent Information Sub-options 5 DHCP relaying 6 Reliability 7 Security 8 IETF standards documents 9 See also 10 Notes 11 References Overview TCP / IP defines how devices on one network communicate with devices on another network, and the DHCP server can manage TCP / IP settings for devices on a network, by automatically or dynamically assigning IP addresses to the devices. The DHCP operates based on the client -- server model. When a computer or other device connects to a network, the DHCP client software sends a DHCP broadcast query requesting the necessary information. Any DHCP server on the network may service the request. The DHCP server manages a pool of IP addresses and information about client configuration parameters such as default gateway, domain name, the name servers, and time servers. On receiving a DHCP request, the DHCP server may respond with specific information for each client, as previously configured by an administrator, or with a specific address and any other information valid for the entire network and for the time period for which the allocation ( lease ) is valid. A DHCP client typically queries for this information immediately after booting, and periodically thereafter before the expiration of the information. When a DHCP client refreshes an assignment, it initially requests the same parameter values, but the DHCP server may assign a new address based on the assignment policies set by administrators. On large networks that consist of multiple links, a single DHCP server may service the entire network when aided by DHCP relay agents located on the interconnecting routers. Such agents relay messages between DHCP clients and DHCP servers located on different subnets. Depending on implementation, the DHCP server may have three methods of allocating IP addresses : Dynamic allocation A network administrator reserves a range of IP addresses for DHCP, and each DHCP client on the LAN is configured to request an IP address from the DHCP server during network initialization. The request - and - grant process uses a lease concept with a controllable time period, allowing the DHCP server to reclaim and then reallocate IP addresses that are not renewed. Automatic allocation The DHCP server permanently assigns an IP address to a requesting client from the range defined by the administrator. This is like dynamic allocation, but the DHCP server keeps a table of past IP address assignments, so that it can preferentially assign to a client the same IP address that the client previously had. Manual allocation ( commonly called static allocation ) The DHCP server issues a private IP address dependent upon each client 's MAC address, based on a predefined mapping by the administrator. This feature is variously called static DHCP assignment by DD - WRT, fixed - address by the dhcpd documentation, address reservation by Netgear, DHCP reservation or static DHCP by Cisco and Linksys, and IP address reservation or MAC / IP address binding by various other router manufacturers. If no match for the client 's MAC address is found, the server may or may not optionally fall back to either Dynamic or Automatic allocation. DHCP is used for Internet Protocol version 4 ( IPv4 ) and IPv6. While both versions serve the same purpose, the details of the protocol for IPv4 and IPv6 differ sufficiently that they may be considered separate protocols. For the IPv6 operation, devices may alternatively use stateless address autoconfiguration. IPv6 hosts may also use link - local addressing to achieve operations restricted to the local network link. Operation An illustration of a typical non-renewing DHCP session ; each message may be either a broadcast or a unicast, depending on the DHCP client capabilities. The DHCP employs a connectionless service model, using the User Datagram Protocol ( UDP ). It is implemented with two UDP port numbers for its operations which are the same as for the BOOTP protocol. UDP port number 67 is the destination port of a server, and UDP port number 68 is used by the client. DHCP operations fall into four phases : server discovery, IP lease offer, IP lease request, and IP lease acknowledgement. These stages are often abbreviated as DORA for discovery, offer, request, and acknowledgement. The DHCP operation begins with clients broadcasting a request. If the client and server are on different subnets, a DHCP Helper or DHCP Relay Agent may be used. Clients requesting renewal of an existing lease may communicate directly via UDP unicast, since the client already has an established IP address at that point. Additionally, there is a BROADCAST ( B ) flag the client can use to indicate in which way ( broadcast or unicast ) it can receive the DHCPOFFER : 0x8000 for broadcast, 0x0000 for unicast. Usually, the DHCPOFFER is sent through unicast. For those hosts which can not accept unicast packets before IP addresses are configured, this flag can be used to work around this issue. DHCP discovery The DHCP client broadcasts a DHCPDISCOVER message on the network subnet using the destination address 255.255. 255.255 or the specific subnet broadcast address. A DHCP client may also request its last - known IP address. If the client remains connected to the same network, the server may grant the request. Otherwise, it depends whether the server is set up as authoritative or not. An authoritative server denies the request, causing the client to issue a new request. A non-authoritative server simply ignores the request, leading to an implementation - dependent timeout for the client to expire the request and ask for a new IP address. For example, if HTYPE is set to 1, to specify that the medium used is Ethernet, HLEN is set to 6 because an Ethernet address ( MAC address ) is 6 octets long. The CHADDR is set to the MAC address used by the client. Some options are set as well. Example DHCPDISCOVER message IP : source = 0.0. 0.0 ; destination = 255.255. 255.255 UDP : source port = 68 ; destination port = 67 Octet 0 Octet 1 Octet 2 Octet 3 OP HTYPE HLEN HOPS 0x01 0x01 0x06 0x00 XID 0x3903F326 SECS FLAGS 0x0000 0x0000 CIADDR ( Client IP address ) 0x00000000 YIADDR ( Your IP address ) 0x00000000 SIADDR ( Server IP address ) 0x00000000 GIADDR ( Gateway IP address ) 0x00000000 CHADDR ( Client hardware address ) 0x00053C04 0x8D590000 0x00000000 0x00000000 192 octets of 0s, or overflow space for additional options ; BOOTP legacy. Magic cookie 0x63825363 DHCP options 0x350101 53 : 1 ( DHCP Discover ) 0x3204c0a00164 50 : 192.168. 1.100 requested 0x370401030f06 55 ( Parameter Request List ) : 1 ( Request Subnet Mask ), 3 ( Router ), 15 ( Domain Name ), 6 ( Domain Name Server ) 0xff 255 ( Endmark ) DHCP offer When a DHCP server receives a DHCPDISCOVER message from a client, which is an IP address lease request, the DHCP server reserves an IP address for the client and makes a lease offer by sending a DHCPOFFER message to the client. This message contains the client 's MAC address, the IP address that the server is offering, the subnet mask, the lease duration, and the IP address of the DHCP server making the offer. The DHCP server determines the configuration based on the client 's hardware address as specified in the CHADDR ( client hardware address ) field. Here the server, 192.168. 1.1, specifies the client 's IP address in the YIADDR ( your IP address ) field. DHCPOFFER message IP : source = 192.168. 1.1 ; destination = 192.168. 1.100 UDP : source port = 67 ; destination port = 68 Octet 0 Octet 1 Octet 2 Octet 3 OP HTYPE HLEN HOPS 0x02 0x01 0x06 0x00 XID 0x3903F326 SECS FLAGS 0x0000 0x0000 CIADDR ( Client IP address ) 0x00000000 YIADDR ( Your IP address ) 0xC0A80164 ( 192.168. 1.100 ) SIADDR ( Server IP address ) 0xC0A80101 ( 192.168. 1.1 ) GIADDR ( Gateway IP address ) 0x00000000 CHADDR ( Client hardware address ) 0x00053C04 0x8D590000 0x00000000 0x00000000 192 octets of 0s ; BOOTP legacy. Magic cookie 0x63825363 DHCP options 53 : 2 ( DHCP Offer ) 1 ( subnet mask ) : 255.255. 255.0 3 ( Router ) : 192.168. 1.1 51 ( IP address lease time ) : 86400s ( 1 day ) 54 ( DHCP server ) : 192.168. 1.1 6 ( DNS servers ) : 9.7. 10.15, 9.7. 10.16, 9.7. 10.18 DHCP request In response to the DHCP offer, the client replies with a DHCPREQUEST message, broadcast to the server, requesting the offered address. A client can receive DHCP offers from multiple servers, but it will accept only one DHCP offer. Based on required server identification option in the request and broadcast messaging, servers are informed whose offer the client has accepted. When other DHCP servers receive this message, they withdraw any offers that they have made to the client and return the offered IP address to the pool of available addresses. DHCPREQUEST message IP : source = 0.0. 0.0 destination = 255.255. 255.255 ; UDP : source port = 68 ; destination port = 67 Octet 0 Octet 1 Octet 2 Octet 3 OP HTYPE HLEN HOPS 0x01 0x01 0x06 0x00 XID 0x3903F326 SECS FLAGS 0x0000 0x0000 CIADDR ( Client IP address ) 0x00000000 YIADDR ( Your IP address ) 0x00000000 SIADDR ( Server IP address ) 0xC0A80101 GIADDR ( Gateway IP address ) 0x00000000 CHADDR ( Client hardware address ) 0x00053C04 0x8D590000 0x00000000 0x00000000 192 octets of 0s ; BOOTP legacy. Magic cookie 0x63825363 DHCP options 53 : 3 ( DHCP Request ) 50 : 192.168. 1.100 requested 54 ( DHCP server ) : 192.168. 1.1 DHCP acknowledgement When the DHCP server receives the DHCPREQUEST message from the client, the configuration process enters its final phase. The acknowledgement phase involves sending a DHCPACK packet to the client. This packet includes the lease duration and any other configuration information that the client might have requested. At this point, the IP configuration process is completed. The protocol expects the DHCP client to configure its network interface with the negotiated parameters. After the client obtains an IP address, it should probe the newly received address ( e.g. with ARP Address Resolution Protocol ) to prevent address conflicts caused by overlapping address pools of DHCP servers. DHCPACK message IP : source = 192.168. 1.1 ; destination = 192.168. 1.100 UDP : source port = 67 ; destination port = 68 Octet 0 Octet 1 Octet 2 Octet 3 OP HTYPE HLEN HOPS 0x02 0x01 0x06 0x00 XID 0x3903F326 SECS FLAGS 0x0000 0x0000 CIADDR ( Client IP address ) 0x00000000 YIADDR ( Your IP address ) 0xC0A80164 SIADDR ( Server IP address ) 0xC0A80101 GIADDR ( Gateway IP address switched by relay ) 0x00000000 CHADDR ( Client hardware address ) 0x00053C04 0x8D590000 0x00000000 0x00000000 192 octets of 0s. BOOTP legacy Magic cookie 0x63825363 DHCP options 53 : 5 ( DHCP ACK ) or 6 ( DHCP NAK ) 1 ( subnet mask ) : 255.255. 255.0 3 ( Router ) : 192.168. 1.1 51 ( IP address lease time ) : 86400s ( 1 day ) 54 ( DHCP server ) : 192.168. 1.1 6 ( DNS servers ) : 9.7. 10.15, 9.7. 10.16, 9.7. 10.18 DHCP information A DHCP client may request more information than the server sent with the original DHCPOFFER. The client may also request repeat data for a particular application. For example, browsers use DHCP Inform to obtain web proxy settings via WPAD. DHCP releasing The client sends a request to the DHCP server to release the DHCP information and the client deactivates its IP address. As client devices usually do not know when users may unplug them from the network, the protocol does not mandate the sending of DHCP Release. Client Configuration parameters A DHCP server can provide optional configuration parameters to the client. RFC 2132 describes the available DHCP options defined by Internet Assigned Numbers Authority ( IANA ) - DHCP and BOOTP PARAMETERS. A DHCP client can select, manipulate and overwrite parameters provided by a DHCP server. In Unix - like systems this client - level refinement typically takes place according to the values in the configuration file / etc / dhclient. conf. DHCP options Options are octet strings of varying length. The first octet is the option code, the second octet is the number of following octets and the remaining octets are code dependent. For example, the DHCP Message type option for an Offer would appear as 0x35, 0x01, 0x02, where 0x35 is code 53 for `` DHCP Message Type '', 0x01 means one octet follows and 0x02 is the value of `` Offer ''. Documented in RFC 2132 The following tables list the available DHCP options, as listed in RFC 2132. RFC 1497 ( BOOTP Vendor Information Extensions ) vendor extensions Code Name Length Notes 0 Pad 0 octets Can be used to pad other options so that they are aligned to the word boundary ; is not followed by length byte Subnet Mask 4 octets Must be sent after the router option ( option 3 ) if both are included Time Offset 4 octets Router Multiples of 4 octets Available routers, should be listed in order of preference Time Server Multiples of 4 octets Available time servers to synchronise with, should be listed in order of preference 5 Name Server Multiples of 4 octets Available IEN 116 name servers, should be listed in order of preference 6 Domain Name Server Multiples of 4 octets Available DNS servers, should be listed in order of preference 7 Log Server Multiples of 4 octets Available log servers, should be listed in order of preference. 8 Cookie Server Multiples of 4 octets `` Cookie '' in this case means `` fortune cookie '' or `` quote of the day, '' a pithy or humorous anecdote often sent as part of a logon process on large computers ; it has nothing to do with cookies sent by websites. 9 LPR Server Multiples of 4 octets 10 Impress Server Multiples of 4 octets 11 Resource Location Server Multiples of 4 octets 12 Host Name Minimum of 1 octet 13 Boot File Size 2 octets Length of the boot image in 4KiB blocks 14 Merit Dump File Minimum of 1 octet Path where crash dumps should be stored 15 Domain Name Minimum of 1 octet 16 Swap Server 4 octets 17 Root Path Minimum of 1 octet 18 Extensions Path Minimum of 1 octet 255 End 0 octets Used to mark the end of the vendor option field IP Layer Parameters per Host Code Name Length Notes 19 IP Forwarding Enable / Disable 1 octet 20 Non-Local Source Routing Enable / Disable 1 octet 21 Policy Filter Multiples of 8 octets 22 Maximum Datagram Reassembly Size 2 octets 23 Default IP Time - to - live 1 octet 24 Path MTU Aging Timeout 4 octets 25 Path MTU Plateau Table Multiples of 2 octets IP Layer Parameters per Interface Code Name Length Notes 26 Interface MTU 2 octets 27 All Subnets are Local 1 octet 28 Broadcast Address 4 octets 29 Perform Mask Discovery 1 octet 30 Mask Supplier 1 octet 31 Perform Router Discovery 1 octet 32 Router Solicitation Address 4 octets 33 Static Route Multiples of 8 octets A list of destination / router pairs Link Layer Parameters per Interface Code Name Length Notes 34 Trailer Encapsulation Option 1 octet 35 ARP Cache Timeout 4 octets 36 Ethernet Encapsulation 1 octet TCP Parameters Code Name Length Notes 37 TCP Default TTL 1 octet 38 TCP Keepalive Interval 4 octets 39 TCP Keepalive Garbage 1 octet Application and Service Parameters Code Name Length Notes 40 Network Information Service Domain Minimum of 1 octet 41 Network Information Servers Multiples of 4 octets 42 Network Time Protocol Servers Multiples of 4 octets 43 Vendor Specific Information Minimum of 1 octets 44 NetBIOS over TCP / IP Name Server Multiples of 4 octets 45 NetBIOS over TCP / IP Datagram Distribution Server Multiples of 4 octets 46 NetBIOS over TCP / IP Node Type 1 octet 47 NetBIOS over TCP / IP Scope Minimum of 1 octet 48 X Window System Font Server Multiples of 4 octets 49 X Window System Display Manager Multiples of 4 octets 64 Network Information Service+ Domain Minimum of 1 octet 65 Network Information Service+ Servers Multiples of 4 octets 68 Mobile IP Home Agent Multiples of 4 octets 69 Simple Mail Transport Protocol ( SMTP ) Server Multiples of 4 octets 70 Post Office Protocol ( POP3 ) Server Multiples of 4 octets 71 Network News Transport Protocol ( NNTP ) Server Multiples of 4 octets 72 Default World Wide Web ( WWW ) Server Multiples of 4 octets 73 Default Finger Server Multiples of 4 octets 74 Default Internet Relay Chat ( IRC ) Server Multiples of 4 octets 75 StreetTalk Server Multiples of 4 octets 76 StreetTalk Directory Assistance ( STDA ) Server Multiples of 4 octets DHCP Extensions Code Name Length Notes 50 Requested IP address 4 octets 51 IP address Lease Time 4 octets 52 Option Overload 1 octet 53 DHCP Message Type 1 octet 54 Server Identifier 4 octets 55 Parameter Request List Minimum of 1 octet 56 Message Minimum of 1 octet 57 Maximum DHCP Message Size 2 octets 58 Renewal ( T1 ) Time Value 4 octets 59 Rebinding ( T2 ) Time Value 4 octets 60 Vendor class identifier Minimum of 1 octet 61 Client - identifier Minimum of 2 octets 66 TFTP server name Minimum of 1 octet 67 Bootfile name Minimum of 1 octet DHCP client Vendor identification An option exists to identify the vendor and functionality of a DHCP client. The information is a variable - length string of characters or octets which has a meaning specified by the vendor of the DHCP client. One method that a DHCP client can utilize to communicate to the server that it is using a certain type of hardware or firmware is to set a value in its DHCP requests called the Vendor Class Identifier ( VCI ) ( Option 60 ). This method allows a DHCP server to differentiate between the two kinds of client machines and process the requests from the two types of modems appropriately. Some types of set - top boxes also set the VCI ( Option 60 ) to inform the DHCP server about the hardware type and functionality of the device. The value this option is set to gives the DHCP server a hint about any required extra information that this client needs in a DHCP response. Documented elsewhere Documented DHCP Options Code Name Length RFC 82 Relay Agent Information Option Minimum of 2 octets RFC 3046 85 NDS Servers Option Minimum of 4 octets, multiple of 4 octets RFC 2241 86 NDS Tree Name Option Variable RFC 2241 87 NDS Context Option Variable RFC 2241 119 Domain Search Option Variable RFC 3397 121 Classless Static Route Option Variable RFC 3442 Relay agent information sub-options The Relay Agent Information Option ( option 82 ) specifies container for attaching sub-options to DHCP requests transmitted between a DHCP relay and a DHCP server. Relay Agent Sub-options Code Name Length RFC DOCSIS ( Data - Over-Cable Service Interface Specifications ) Device Class 4 octets RFC 3256 DHCP relaying In small networks, where only one IP subnet is being managed, DHCP clients communicate directly with DHCP servers. However, DHCP servers can also provide IP addresses for multiple subnets. In this case, a DHCP client that has not yet acquired an IP address can not communicate directly with the DHCP server using IP routing, because it does n't have a routable IP address, does n't know the IP address of a router, and does n't know the IP address of the DHCP server. In order to allow DHCP clients on subnets not directly served by DHCP servers to communicate with DHCP servers, DHCP relay agents can be installed on these subnets. The DHCP client broadcasts on the local link ; the relay agent receives the broadcast and transmits it to one or more DHCP servers using unicast. The relay agent stores its own IP address in field GIADDR field of the DHCP packet. The DHCP server uses the GIADDR - value to determine the subnet on which the relay agent received the broadcast, and allocates an IP address on that subnet. When the DHCP server replies to the client, it sends the reply to the GIADDR - address, again using unicast. The relay agent then retransmits the response on the local network. In this situation, the communication between the relay agent and the DHCP server typically uses both a source and destination UDP port of 67. Reliability The DHCP ensures reliability in several ways : periodic renewal, rebinding, and failover. DHCP clients are allocated leases that last for some period of time. Clients begin to attempt to renew their leases once half the lease interval has expired. They do this by sending a unicast DHCPREQUEST message to the DHCP server that granted the original lease. If that server is down or unreachable, it will fail to respond to the DHCPREQUEST. However, in that case the client repeats the DHCPREQUEST from time to time, so if the DHCP server comes back up or becomes reachable again, the DHCP client will succeed in contacting it and renew the lease. If the DHCP server is unreachable for an extended period of time, the DHCP client will attempt to rebind, by broadcasting its DHCPREQUEST rather than unicasting it. Because it is broadcast, the DHCPREQUEST message will reach all available DHCP servers. If some other DHCP server is able to renew the lease, it will do so at this time. In order for rebinding to work, when the client successfully contacts a backup DHCP server, that server must have accurate information about the client 's binding. Maintaining accurate binding information between two servers is a complicated problem ; if both servers are able to update the same lease database, there must be a mechanism to avoid conflicts between updates on the independent servers. A proposal for implementing fault - tolerant DHCP servers was submitted to the Internet Engineering Task Force, but never formalized If rebinding fails, the lease will eventually expire. When the lease expires, the client must stop using the IP address granted to it in its lease. At that time it will restart the DHCP process from the beginning by broadcasting a DHCPDISCOVER message. Since its lease has expired, it will accept any IP address offered to it. Once it has a new IP address ( presumably from a different DHCP server ) it will once again be able to use the network. However, since its IP address has changed, any ongoing connections will be broken. Security See also : DHCP snooping The base DHCP does not include any mechanism for authentication. Because of this, it is vulnerable to a variety of attacks. These attacks fall into three main categories : Unauthorized DHCP servers providing false information to clients. Unauthorized clients gaining access to resources. Resource exhaustion attacks from malicious DHCP clients. Because the client has no way to validate the identity of a DHCP server, unauthorized DHCP servers ( commonly called `` rogue DHCP '' ) can be operated on networks, providing incorrect information to DHCP clients. This can serve either as a denial - of - service attack, preventing the client from gaining access to network connectivity, or as a man - in - the - middle attack. Because the DHCP server provides the DHCP client with server IP addresses, such as the IP address of one or more DNS servers, an attacker can convince a DHCP client to do its DNS lookups through its own DNS server, and can therefore provide its own answers to DNS queries from the client. This in turn allows the attacker to redirect network traffic through itself, allowing it to eavesdrop on connections between the client and network servers it contacts, or to simply replace those network servers with its own. Because the DHCP server has no secure mechanism for authenticating the client, clients can gain unauthorized access to IP addresses by presenting credentials, such as client identifiers, that belong to other DHCP clients. This also allows DHCP clients to exhaust the DHCP server 's store of IP addresses -- by presenting new credentials each time it asks for an address, the client can consume all the available IP addresses on a particular network link, preventing other DHCP clients from getting service. DHCP does provide some mechanisms for mitigating these problems. The Relay Agent Information Option protocol extension ( RFC 3046, usually referred to in the industry by its actual number as Option 82 ) allows network operators to attach tags to DHCP messages as these messages arrive on the network operator 's trusted network. This tag is then used as an authorization token to control the client 's access to network resources. Because the client has no access to the network upstream of the relay agent, the lack of authentication does not prevent the DHCP server operator from relying on the authorization token. Another extension, Authentication for DHCP Messages ( RFC 3118 ), provides a mechanism for authenticating DHCP messages. Unfortunately, as of 2002, RFC 3118 had not seen widespread adoption because of the problems of managing keys for large numbers of DHCP clients. A 2007 book about DSL technologies remarked that there were numerous security vulnerabilities identified against the security measures proposed by RFC 3118. This fact, combined with the introduction of 802.1 x, slowed the deployment and take - rate of authenticated DHCP, and it has never been widely deployed. A 2010 book notes that ( t ) here have been very few implementations of DHCP Authentication. The challenges of key management and processing delays due to hash computation have been deemed too heavy a price to pay for the perceived benefits. Architectural proposals from 2008 involve authenticating DHCP requests using 802.1 x or PANA ( both of which transport EAP ). An IETF proposal was made for including EAP in DHCP itself, the so - called EAPoDHCP ; this does not appear to have progressed beyond IETF draft level, the last of which dates to 2010. IETF standards documents RFC 2131, Dynamic Host Configuration Protocol RFC 2132, DHCP Options and BOOTP Vendor Extensions RFC 3046, DHCP Relay Agent Information Option RFC 3397, Dynamic Host Configuration Protocol ( DHCP ) Domain Search Option RFC 3942, Reclassifying Dynamic Host Configuration Protocol Version Four ( DHCPv4 ) Options RFC 4242, Information Refresh Time Option for Dynamic Host Configuration Protocol for IPv6 RFC 4361, Node - specific Client Identifiers for Dynamic Host Configuration Protocol Version Four ( DHCPv4 ) RFC 4436, Detecting Network Attachment in IPv4 ( DNAv4 ) RFC 3442, Classless Static Route Option for Dynamic Host Configuration Protocol ( DHCP ) version 4 See also Computer networking portal Boot Service Discovery Protocol ( BSDP ) -- a DHCP extension used by Apple 's NetBoot Comparison of DHCP server software Peg DHCP ( RFC 2322 ) Preboot Execution Environment ( PXE ) Reverse Address Resolution Protocol ( RARP ) Rogue DHCP UDP Helper Address -- a tool for routing DHCP requests across subnet boundaries Zeroconf -- Zero Configuration Networking Notes ^ Jump up to : As an optional client behavior, some broadcasts, such as those carrying DHCP discovery and request messages, may be replaced with unicasts in case the DHCP client already knows the DHCP server 's IP address. Jump up ^ The RFC calls for the client to wait one half of the remaining time until T2 before it retransmits the DHCPREQUEST packet Jump up ^ The proposal provided a mechanism whereby two servers could remain loosely in sync with each other in such a way that even in the event of a total failure of one server, the other server could recover the lease database and continue operating. Due to the length and complexity of the specification, it was never published as a standard ; however, the techniques described in the specification are in wide use, with one open - source implementation in the ISC DHCP server, as well as several commercial implementations. References ^ Jump up to : TechTarget Network : DHCP ( Dynamic Host Configuration Protocol ) Jump up ^ Peterson LL, Davie BS. ( 2011 ). Computer Networks : A Systems Approach. Jump up ^ Ralph Droms ; Ted Lemon ( 2003 ). The DHCP Handbook. SAMS Publishing. p. 436. ISBN 0 - 672 - 32327 - 3. Jump up ^ Droms, Ralph. `` Dynamic Host Configuration Protocol ''. tools.ietf.org. Retrieved 4 July 2017. Jump up ^ Droms, Ralph. `` Dynamic Host Configuration Protocol ''. tools.ietf.org. Retrieved 2015 - 12 - 26. Jump up ^ Droms, Ralph. `` Dynamic Host Configuration Protocol ''. tools.ietf.org. Retrieved 4 July 2017. ^ Jump up to : Droms, Ralph ( March 1997 ). DHCP Options and BOOTP Vendor Extensions. IETF. doi : 10.17487 / RFC2131. RFC 2131. https://tools.ietf.org/html/rfc2131. Retrieved September 9, 2014. Jump up ^ RFC2131 Dynamic Host Configuration Protocol : Dynamic allocation of network addresses http://tools.ietf.org/html/rfc2131#section-2.2 Jump up ^ `` Dynamic Host Configuration Protocol ( DHCP ) and Bootstrap Protocol ( BOOTP ) Parameters ''. Iana.org. Retrieved 2013 - 11 - 28. ^ Jump up to : Alexander, Steve ; Droms, Ralph ( March 1997 ). DHCP Options and BOOTP Vendor Extensions. IETF. doi : 10.17487 / RFC2132. RFC 2132. https://tools.ietf.org/html/rfc2132. Retrieved June 10, 2012. ^ Jump up to : Patrick, Michael ( January 2001 ). `` DHCP Relay Agent Information Option ''. IETF Documents. IETF. doi : 10.17487 / RFC3046. Retrieved 22 July 2017. ^ Jump up to : Provan, Don ( November 1997 ). `` RFC 2241 - DHCP Options for Novell Directory Services ''. IETF Documents. IETF. doi : 10.17487 / RFC3256. Retrieved 23 July 2017. Jump up ^ Bernard, Aboba ; Stuart, Cheshire ( November 2002 ). `` RFC 3397 - Dynamic Host Configuration Protocol ( DHCP ) Domain Search Option ''. IETF Documents. IETF. doi : 10.17487 / RFC3397. Retrieved 22 July 2017. Jump up ^ RFC 3442 Jump up ^ Doug, Jones, ; Rich, Woundy, ( April 2002 ). `` RFC 3256 - The DOCSIS ( Data - Over-Cable Service Interface Specifications ) Device Class DHCP ( Dynamic Host Configuration Protocol ) Relay Agent Information Sub-option ''. IETF Documents. IETF. doi : 10.17487 / RFC3256. Retrieved 23 July 2017. Jump up ^ Droms, Ralph ; Kinnear, Kim ; Stapp, Mark ; Volz, Bernie ; Gonczi, Steve ; Rabil, Greg ; Dooley, Michael ; Kapur, Arun ( March 2003 ). DHCP Failover Protocol. IETF. I-D draft - ietf - dhc - failover - 12. https://tools.ietf.org/html/draft-ietf-dhc-failover-12. Retrieved May 09, 2010. ^ Jump up to : Michael Patrick ( January 2001 ). `` RFC 3046 - DHCP Relay Agent Information Option ''. Network Working Group. ^ Jump up to : Ralph Droms ( March 1997 ). `` RFC 2131 - Dynamic Host Configuration Protocol ''. Network Working Group. ^ Jump up to : Timothy Stapko ( 2011 ). Practical Embedded Security : Building Secure Resource - Constrained Systems. Newnes. p. 39. ISBN 978 - 0 - 08 - 055131 - 9. Jump up ^ Derrick Rountree ( 2013 ). Windows 2012 Server Network Security : Securing Your Windows Network Systems and Infrastructure. Newnes. p. 22. ISBN 978 - 1 - 59749 - 965 - 1. Jump up ^ Timothy Rooney ( 2010 ). Introduction to IP Address Management. John Wiley & Sons. p. 180. ISBN 978 - 1 - 118 - 07380 - 3. ^ Jump up to : Sergey Golovanov ( Kaspersky Labs ) ( June 2011 ). `` TDSS loader now got `` legs '' ``. Jump up ^ Akash K Sunny ( October 2015 ). `` dhcp protocol and its vulnerabilities ''. Jump up ^ Francisco J. Hens ; José M. Caballero ( 2008 ). Triple Play : Building the converged network for IP, VoIP and IPTV. John Wiley & Sons. p. 239. ISBN 978 - 0 - 470 - 75439 - 9. Jump up ^ David H. Ramirez ( 2008 ). IPTV Security : Protecting High - Value Digital Contents. John Wiley & Sons. p. 55. ISBN 978 - 0 - 470 - 72719 - 5. Jump up ^ Ted Lemon ( April 2002 ). `` Implementation of RFC 3118 ''. Jump up ^ Philip Golden ; Hervé Dedieu ; Krista S. Jacobsen ( 2007 ). Implementation and Applications of DSL Technology. Taylor & Francis. p. 484. ISBN 978 - 1 - 4200 - 1307 - 8. Jump up ^ Timothy Rooney ( 2010 ). Introduction to IP Address Management. John Wiley & Sons. pp. 181 -- 182. ISBN 978 - 1 - 118 - 07380 - 3. Jump up ^ Rebecca Copeland ( 2008 ). Converging NGN Wireline and Mobile 3G Networks with IMS. Taylor & Francis. pp. 142 -- 143. ISBN 978 - 1 - 4200 - 1378 - 8. Jump up ^ Ramjee Prasad ; Albena Mihovska ( 2009 ). New Horizons in Mobile and Wireless Communications : Networks, services, and applications. 2. Artech House. p. 339. ISBN 978 - 1 - 60783 - 970 - 5. Jump up ^ `` Archived copy ''. Archived from the original on 2015 - 04 - 03. Retrieved 2013 - 12 - 12. Wikimedia Commons has media related to Dynamic Host Configuration Protocol ( DHCP ). GND : 4608416 - 2 Retrieved from `` https://en.wikipedia.org/w/index.php?title=Dynamic_Host_Configuration_Protocol&oldid=833845039 '' Categories : Internet Standards Application layer protocols Network service Hidden categories : Wikipedia introduction cleanup from November 2015 All pages needing cleanup Articles covered by WikiProject Wikify from November 2015 All articles covered by WikiProject Wikify Articles needing additional references from April 2014 All articles needing additional references Articles with multiple maintenance issues Wikipedia articles with GND identifiers Pages using RFC magic links Talk Contents About Wikipedia Afrikaans Azərbaycanca Български Boarisch Bosanski Català Čeština Dansk Deutsch Eesti Ελληνικά Español Euskara فارسی Français 한국어 हिन्दी Hrvatski Bahasa Indonesia Italiano עברית Latviešu Lumbaart Magyar Македонски മലയാളം Bahasa Melayu Монгол Nederlands 日本 語 Norsk Norsk nynorsk Polski Português Română Русский Scots Shqip Simple English Slovenčina Slovenščina Српски / srpski Srpskohrvatski / српскохрватски Suomi Svenska தமிழ் ไทย Türkçe Українська Tiếng Việt Yorùbá 粵語 中文 45 more Edit links This page was last edited on 2 April 2018, at 18 : 02. 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Question: final step of the dhcp discovery process is known as
Answer: IP lease acknowledgement