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RFC 1531 http://tools.ietf.org/html/rfc1531
RFC 2131 http://tools.ietf.org/html/rfc2131

The Dynamic Host Configuration Protocol (DHCP) provides Internet hosts with configuration parameters. DHCP is an extension of BOOTP. DHCP consists of two components: a protocol for delivering host-specific configuration parameters from a DHCP server to a host and a mechanism for allocation of network addresses to hosts.
(Compliant with IETF RFC1531.)

The format of the header is shown in the following illustration:

8
16
24
32 bits

Op (1)

Htype (1)

Hlen (1) 

  Hops (1)

Xid (4 bytes)

Secs (2 bytes)

Flags (2 bytes)

Ciaddr (4 bytes)

Yiaddr (4 bytes)

Siaddr (4 bytes)

Giaddr (4 bytes)


Chaddr (16 bytes)
 

DHCP header structure
 

Op
The message operation code. Messages can be either BOOTREQUEST or BOOTREPLY.

Htype
The hardware address type.

Hlen
The hardware address length.

Xid
The transaction ID.

Secs
The seconds elapsed since the client began the address acquisition or renewal process.

Flags
The flags.

Ciaddr
The client IP address.

Yiaddr
The "Your" (client) IP address.

Siaddr
The IP address of the next server to use in bootstrap.

Giaddr
The relay agent IP address used in booting via a relay agent.

Chaddr
The client hardware address.

Vulnerabilities for this protocol (from CVE)

CVE ID Protocol Source Port Targetport

TCP/IP Protocols:

AHARP/RARPATMPBGP-4COPSDCAPDHCPDNS
DVMRPEGPEIGRPESPFANPFingerFTPHSRP
HTTPICMPICMPv6IGMPIGRPIMAP4IPIPDC
IPv6ISAKMPL2FL2TPLDAPMARSMobile IPNARP
NetBIOS/IPNHRPNTPOSPFPIMPOP3PPTPRadius
RIP2RIPng for IPv6RLOGINRSVPRTSPRUDPS-HTTPSCTP
SLPSMTPSNMPSOCKS V5TACACSTALITCPTELNET
TFTPUDPVan JacobsonVRRPWCCPX-WindowXOT