dhcp

Documentation

Index

• Constants
• func ForEachOption(udpPayload []byte, fn func(opt Option) error) error
• type ClientState
  • func (s ClientState) IsValid() bool
  • func (i ClientState) String() string
• type HeaderV4
  • func DecodeHeaderV4(src []byte) (d HeaderV4)
  • func (dhdr *HeaderV4) Put(dst []byte)
  • func (dhdr *HeaderV4) String() (s string)
• type MessageType
  • func (i MessageType) String() string
• type Op
• type OptNum
  • func (i OptNum) String() string
• type Option
  • func (opt *Option) Encode(dst []byte) (int, error)
  • func (opt *Option) String() string

Constants

const (
	SizeHeader = 44
	// Magic Cookie offset measured from the start of the UDP payload.
	MagicCookieOffset = SizeHeader + sizeSName + sizeBootFile
	// Expected Magic Cookie value.
	MagicCookie uint32 = 0x63825363
	// DHCP Options offset measured from the start of the UDP payload.
	OptionsOffset = MagicCookieOffset + 4

	DefaultClientPort = 68
	DefaultServerPort = 67
)

Functions

func ForEachOption

func ForEachOption(udpPayload []byte, fn func(opt Option) error) error

Types

type ClientState

type ClientState uint8

ClientState represents the state of a DHCP client. Below is a state diagram of a DHCP client.

const (

	// On clean slate boot, abort, NAK or decline enter the INIT state.
	StateInit ClientState
	// After sending out a Discover enter SELECTING.
	StateSelecting
	// After receiving a worthy offer enter REQUESTING.
	StateRequesting
	// On reboot enter INIT-REBOOT state.
	// StateInitReboot
	// On sending out a Request enter REBOOTING.
	// StateRebooting
	// On ACK to Request enter BOUND.
	StateBound
)

install stringer with `go install golang.org/x/tools/cmd/stringer@latest`

func (ClientState) IsValid

func (s ClientState) IsValid() bool

IsValid returns true if the state is within the valid range.

func (ClientState) String

func (i ClientState) String() string

type HeaderV4

type HeaderV4 struct {
	OP Op // 0:1
	// Htype is the hardware address type. 1 for Ethernet.
	HType byte   // 1:2
	HLen  uint8  // 2:3
	HOps  uint8  // 3:4
	Xid   uint32 // 4:8
	Secs  uint16 // 8:10
	Flags uint16 // 10:12
	// CIAddr is the client IP address. If the client has not obtained an IP
	// address yet, this field is set to 0.
	CIAddr [4]byte // 12:16
	// YIAddr is the IP address offered by the server to the client.
	YIAddr [4]byte // 16:20
	// SIAddr is the IP address of the next server to use in bootstrap. This
	// field is used in DHCPOFFER and DHCPACK messages.
	SIAddr [4]byte // 20:24
	// GIAddr is the gateway IP address.
	GIAddr [4]byte // 24:28
	// CHAddr is the client hardware address. Can be up to 16 bytes in length but
	// is usually 6 bytes for Ethernet.
	CHAddr [16]byte // 28:44

}

HeaderV4 specifies the first 44 bytes of a DHCP packet payload. It does not include BOOTP, magic cookie and options. Reference: https://lists.gnu.org/archive/html/lwip-users/2012-12/msg00016.html

func DecodeHeaderV4

func DecodeHeaderV4(src []byte) (d HeaderV4)

func (*HeaderV4) Put

func (dhdr *HeaderV4) Put(dst []byte)

func (*HeaderV4) String

func (dhdr *HeaderV4) String() (s string)

type MessageType

type MessageType uint8

const (
	MsgDiscover MessageType = iota + 1
	MsgOffer
	MsgRequest
	MsgDecline
	MsgAck
	MsgNak
	MsgRelease
	MsgInform
)

func (MessageType) String

func (i MessageType) String() string

type Op

type Op byte

const (
	OpRequest Op = 1
	OpReply   Op = 2
)

type OptNum

type OptNum uint8

const (
	OptWordAligned                 OptNum = 0
	OptSubnetMask                  OptNum = 1
	OptTimeOffset                  OptNum = 2  // Time offset in seconds from UTC
	OptRouter                      OptNum = 3  // N/4 router addresses
	OptTimeServers                 OptNum = 4  // N/4 time server addresses
	OptNameServers                 OptNum = 5  // N/4 IEN-116 server addresses
	OptDNSServers                  OptNum = 6  // N/4 DNS server addresses
	OptLogServers                  OptNum = 7  // N/4 logging server addresses
	OptCookieServers               OptNum = 8  // N/4 quote server addresses
	OptLPRServers                  OptNum = 9  // N/4 printer server addresses
	OptImpressServers              OptNum = 10 // N/4 impress server addresses
	OptRLPServers                  OptNum = 11 // N/4 RLP server addresses
	OptHostName                    OptNum = 12 // Hostname string
	OptBootFileSize                OptNum = 13 // Size of boot file in 512 byte chunks
	OptMeritDumpFile               OptNum = 14 // Client to dump and name of file to dump to
	OptDomainName                  OptNum = 15 // The DNS domain name of the client
	OptSwapServer                  OptNum = 16 // Swap server addresses
	OptRootPath                    OptNum = 17 // Path name for root disk
	OptExtensionFile               OptNum = 18 // Patch name for more BOOTP info
	OptIPLayerForwarding           OptNum = 19 // Enable or disable IP forwarding
	OptSrcrouteenabler             OptNum = 20 // Enable or disable source routing
	OptPolicyFilter                OptNum = 21 // Routing policy filters
	OptMaximumDGReassemblySize     OptNum = 22 // Maximum datagram reassembly size
	OptDefaultIPTTL                OptNum = 23 // Default IP time-to-live
	OptPathMTUAgingTimeout         OptNum = 24 // Path MTU aging timeout
	OptMTUPlateau                  OptNum = 25 // Path MTU plateau table
	OptInterfaceMTUSize            OptNum = 26 // Interface MTU size
	OptAllSubnetsAreLocal          OptNum = 27 // All subnets are local
	OptBroadcastAddress            OptNum = 28 // Broadcast address
	OptPerformMaskDiscovery        OptNum = 29 // Perform mask discovery
	OptProvideMasktoOthers         OptNum = 30 // Provide mask to others
	OptPerformRouterDiscovery      OptNum = 31 // Perform router discovery
	OptRouterSolicitationAddress   OptNum = 32 // Router solicitation address
	OptStaticRoutingTable          OptNum = 33 // Static routing table
	OptTrailerEncapsulation        OptNum = 34 // Trailer encapsulation
	OptARPCacheTimeout             OptNum = 35 // ARP cache timeout
	OptEthernetEncapsulation       OptNum = 36 // Ethernet encapsulation
	OptDefaultTCPTimetoLive        OptNum = 37 // Default TCP time to live
	OptTCPKeepaliveInterval        OptNum = 38 // TCP keepalive interval
	OptTCPKeepaliveGarbage         OptNum = 39 // TCP keepalive garbage
	OptNISDomainName               OptNum = 40 // NIS domain name
	OptNISServerAddresses          OptNum = 41 // NIS server addresses
	OptNTPServersAddresses         OptNum = 42 // NTP servers addresses
	OptVendorSpecificInformation   OptNum = 43 // Vendor specific information
	OptNetBIOSNameServer           OptNum = 44 // NetBIOS name server
	OptNetBIOSDatagramDistribution OptNum = 45 // NetBIOS datagram distribution
	OptNetBIOSNodeType             OptNum = 46 // NetBIOS node type
	OptNetBIOSScope                OptNum = 47 // NetBIOS scope
	OptXWindowFontServer           OptNum = 48 // X window font server
	OptXWindowDisplayManager       OptNum = 49 // X window display manager
	OptRequestedIPaddress          OptNum = 50 // Requested IP address
	OptIPAddressLeaseTime          OptNum = 51 // IP address lease time
	OptOptionOverload              OptNum = 52 // Overload “sname” or “file”
	OptMessageType                 OptNum = 53 // DHCP message type.
	OptServerIdentification        OptNum = 54 // DHCP server identification
	OptParameterRequestList        OptNum = 55 // Parameter request list
	OptMessage                     OptNum = 56 // DHCP error message
	OptMaximumMessageSize          OptNum = 57 // DHCP maximum message size
	OptRenewTimeValue              OptNum = 58 // DHCP renewal (T1) time
	OptRebindingTimeValue          OptNum = 59 // DHCP rebinding (T2) time
	OptClientIdentifier            OptNum = 60 // Client identifier
	OptClientIdentifier1           OptNum = 61 // Client identifier
)

DHCP options. Taken from https://help.sonicwall.com/help/sw/eng/6800/26/2/3/content/Network_DHCP_Server.042.12.htm.

func (OptNum) String

func (i OptNum) String() string

type Option

type Option struct {
	Num  OptNum
	Data []byte
}

func (*Option) Encode

func (opt *Option) Encode(dst []byte) (int, error)

func (*Option) String

func (opt *Option) String() string