Hans.IP4.Dhcp.Packet

The Dhcp4 module defines the various messages and transitions used in the DHCPv4 protocol. This module provides both a high-level view of the message types as well as a low-level intermediate form which is closely tied to the binary format.

References: RFC 2131 - Dynamic Host Configuration Protocol http://www.faqs.org/rfcs/rfc2131.html

High-level client types

data RequestMessage

RequestMessage is a sum of the client request messages.

Constructors

RequestMessage !Request

DiscoverMessage !Discover

Instances

Show RequestMessage

Methods

showsPrec :: Int -> RequestMessage -> ShowS

show :: RequestMessage -> String

showList :: [RequestMessage] -> ShowS

data Request

Request is used by the client to accept an offered lease.

Constructors

Request

Fields

• requestXid :: !Xid

  Transaction ID of offer

• requestBroadcast :: Bool

  Set True to instruct server to send to broadcast hardware address

• requestServerAddr :: !IP4
• requestClientHardwareAddress :: !Mac

  Hardware address of the client

• requestParameters :: [Dhcp4OptionTag]

  Used to specify the information that client needs

• requestAddress :: Maybe IP4

  Used to specify the address which was accepted

Instances

Show Request

Methods

showsPrec :: Int -> Request -> ShowS

show :: Request -> String

showList :: [Request] -> ShowS

data Discover

Discover is used by the client to discover what servers are available. This message is sent to the IPv4 broadcast.

Constructors

Discover

Fields

• discoverXid :: !Xid

  Transaction ID of this and subsequent messages

• discoverBroadcast :: Bool

  Set True to instruct the server to send to broadcast hardware address

• discoverClientHardwareAddr :: !Mac

  Hardware address of the client

• discoverParameters :: [Dhcp4OptionTag]

  Used to specify the information that client needs in the offers

Instances

Show Discover

Methods

showsPrec :: Int -> Discover -> ShowS

show :: Discover -> String

showList :: [Discover] -> ShowS

High-level server types

data ServerSettings

ServerSettings define all of the information that would be needed to act as a DHCP server for one client. The server is defined to be able to issue a single "lease" whose parameters are defined below.

Constructors

Settings

Fields

• staticServerAddr :: !IP4

  The IPv4 address of the DHCP server

• staticTimeOffset :: !Word32

  Lease: timezone offset in seconds from UTC

• staticClientAddr :: !IP4

  Lease: client IPv4 address on network

• staticLeaseTime :: !Word32

  Lease: duration in seconds

• staticSubnet :: !SubnetMask

  Lease: subnet mask on network

• staticBroadcast :: !IP4

  Lease: broadcast address on network

• staticRouters :: [IP4]

  Lease: gateway routers on network

• staticDomainName :: String

  Lease: client's assigned domain name

• staticDNS :: [IP4]

  Lease: network DNS servers

Instances

Show ServerSettings

Methods

showsPrec :: Int -> ServerSettings -> ShowS

show :: ServerSettings -> String

showList :: [ServerSettings] -> ShowS

data ReplyMessage

ReplyMessage is a sum of the server response messages.

Constructors

AckMessage !Ack

OfferMessage !Offer

Instances

Show ReplyMessage

Methods

showsPrec :: Int -> ReplyMessage -> ShowS

show :: ReplyMessage -> String

showList :: [ReplyMessage] -> ShowS

data Ack

Ack is sent by the DHCPv4 server to acknowledge a sucessful Request message. Upon receiving this message the client has completed the exchange and has successfully obtained a lease.

Constructors

Ack

Fields

• ackHops :: !Word8

  The maximum number of relays this message can use.

• ackXid :: !Xid

  Transaction ID for this exchange

• ackYourAddr :: !IP4

  Lease: assigned client address

• ackServerAddr :: !IP4

  DHCP server's IPv4 address

• ackRelayAddr :: !IP4

  DHCP relay server's address

• ackClientHardwareAddr :: !Mac

  Client's hardware address

• ackLeaseTime :: !Word32

  Lease: duration of lease in seconds

• ackOptions :: [Dhcp4Option]

  Subset of information requested in previous Request

Instances

Show Ack

Methods

showsPrec :: Int -> Ack -> ShowS

show :: Ack -> String

showList :: [Ack] -> ShowS

data Offer

Offer is sent by the DHCPv4 server in response to a Discover. This offer is only valid for a short period of time as the client might receive many offers. The client must next request a lease from a specific server using the information in that server's offer.

Constructors

Offer

Fields

• offerHops :: !Word8

  The maximum number of relays this message can use.

• offerXid :: !Xid

  Transaction ID of this exchange

• offerYourAddr :: !IP4

  The IPv4 address that this server is willing to lease

• offerServerAddr :: !IP4

  The IPv4 address of the DHCPv4 server

• offerRelayAddr :: !IP4

  The IPv4 address of the DHCPv4 relay server

• offerClientHardwareAddr :: !Mac

  The hardware address of the client

• offerOptions :: [Dhcp4Option]

  The options that this server would include in a lease

Instances

Show Offer

Methods

showsPrec :: Int -> Offer -> ShowS

show :: Offer -> String

showList :: [Offer] -> ShowS

Low-level message types

data Dhcp4Message

Dhcp4Message is a low-level message container that is very close to the binary representation of DHCPv4 message. It is suitable for containing any DHCPv4 message. Values of this type should only be created using the publicly exported functions.

Constructors

Dhcp4Message

Fields

• dhcp4Op :: Dhcp4Op

  Message op code / message type. 1 = BOOTREQUEST, 2 = BOOTREPLY

• dhcp4Hops :: !Word8

  Client sets to zero, optionally used by relay agents when booting via a relay agent.

• dhcp4Xid :: !Xid

  Transaction ID, a random number chosen by the client, used by the client and server to associate messages and responses between a client and a server.

• dhcp4Secs :: !Word16

  Filled in by client, seconds elapsed since client began address acquisition or renewal process.

• dhcp4Broadcast :: Bool

  Client requests messages be sent to hardware broadcast address

• dhcp4ClientAddr :: !IP4

  Client IP address; only filled in if client is in BOUND, RENEW or REBINDING state and can respond to ARP requests.

• dhcp4YourAddr :: !IP4

  your (client) address

• dhcp4ServerAddr :: !IP4

  IP address of next server to use in bootstrap; returned in DHCPOFFER, DHCPACK by server

• dhcp4RelayAddr :: !IP4

  Relay agent IP address, used in booting via a relay agent

• dhcp4ClientHardwareAddr :: !Mac

  Client hardware address

• dhcp4ServerHostname :: String

  Optional server host name, null terminated string

• dhcp4BootFilename :: String

  Boot file name, full terminated string; "generic" name of null in DHCPDISCOVER, fully qualified directory-path name in DHCPOFFER

• dhcp4Options :: [Dhcp4Option]

  Optional parameters field.

Instances

Eq Dhcp4Message

Methods

(==) :: Dhcp4Message -> Dhcp4Message -> Bool

(/=) :: Dhcp4Message -> Dhcp4Message -> Bool

Show Dhcp4Message

Methods

showsPrec :: Int -> Dhcp4Message -> ShowS

show :: Dhcp4Message -> String

showList :: [Dhcp4Message] -> ShowS

newtype Xid

Xid is a Transaction ID, a random number chosen by the client, used by the client and server to associate messages and responses between a client and a server.

Constructors

Xid Word32

Instances

Eq Xid

Methods

(==) :: Xid -> Xid -> Bool

(/=) :: Xid -> Xid -> Bool

Show Xid

Methods

showsPrec :: Int -> Xid -> ShowS

show :: Xid -> String

showList :: [Xid] -> ShowS

CodecAtom Xid

Methods

getAtom :: Get Xid

putAtom :: Xid -> Put

atomSize :: Xid -> Int

Server message transition logic

requestToAck

Arguments

:: ServerSettings

DHCPv4 server settings

-> Request

Client's request message

-> Ack

requestToAck creates Ack messages suitable for responding to Request messages given a static ServerSettings configuration.

discoverToOffer

Arguments

:: ServerSettings

DHCPv4 server settings

-> Discover

Client's discover message

-> Offer

discoverToOffer creates a suitable Offer in response to a client's Discover message using the configuration settings specified in the given ServerSettings.

Client message transition logic

mkDiscover

Arguments

:: Xid

New randomly generated transaction ID

-> Mac

The client's hardware address

-> Discover

mkDiscover creates a new Discover message with a set of options suitable for configuring a basic network stack.

offerToRequest

Arguments

:: Offer

The offer as received from the server

-> Request

offerToRequest creates a Request message suitable for accepting an Offer from the DHCPv4 server.

Convert high-level message types to low-level format

requestToMessage :: Request -> Dhcp4Message

requestToMessage embeds Request messages in the low-level Dhcp4Message type, typically for the purpose of serialization.

ackToMessage :: Ack -> Dhcp4Message

ackToMessage embeds Ack messages in the low-level Dhcp4Message type, typically for the purpose of serialization.

offerToMessage :: Offer -> Dhcp4Message

offerToMessage embeds Offer messages in the low-level Dhcp4Message type, typically for the purpose of serialization.

discoverToMessage :: Discover -> Dhcp4Message

discoverToMessage embeds Discover messages in the low-level Dhcp4Message type, typically for the purpose of serialization.

Convert low-level message type to high-level format

parseDhcpMessage :: Dhcp4Message -> Maybe (Either RequestMessage ReplyMessage)

parseDhcpMessage attempts to find a valid high-level message contained in a low-level message. The Dhcp4Message is a large type and can encode invalid combinations of options.

Convert low-level message type to binary format

getDhcp4Message :: Get Dhcp4Message

getDhcp4Message is the binary decoder for parsing Dhcp4Message values.

putDhcp4Message :: Dhcp4Message -> Put

getDhcp4Message is the binary encoder for rendering Dhcp4Message values.