DHCP

DHCP packet parser/serializer

class os_ken.lib.packet.dhcp.dhcp(op, chaddr, options=None, htype=1, hlen=0, hops=0, xid=None, secs=0, flags=0, ciaddr='0.0.0.0', yiaddr='0.0.0.0', siaddr='0.0.0.0', giaddr='0.0.0.0', sname='', boot_file='')

DHCP (RFC 2131) header encoder/decoder class.

The serialized packet would looks like the ones described in the following sections.

  • RFC 2131 DHCP packet format

An instance has the following attributes at least. Most of them are same to the on-wire counterparts but in host byte order. __init__ takes the corresponding args in this order.

Attribute

Description

op

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

htype

Hardware address type (e.g. '1' = 10mb ethernet).

hlen

Hardware address length (e.g. '6' = 10mb ethernet).

hops

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

xid

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

secs

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

flags

Flags.

ciaddr

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

yiaddr

'your' (client) IP address.

siaddr

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

giaddr

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

chaddr

Client hardware address.

sname

Optional server host name, null terminated string.

boot_file

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

options

Optional parameters field ('DHCP message type' option must be included in every DHCP message).
classmethod parser(buf)

Decode a protocol header.

This method is used only when decoding a packet.

Decode a protocol header at offset 0 in bytearray buf. Returns the following three objects.

  • An object to describe the decoded header.

  • A packet_base.PacketBase subclass appropriate for the rest of the packet. None when the rest of the packet should be considered as raw payload.

  • The rest of packet.

serialize(_payload=None, _prev=None)

Encode a protocol header.

This method is used only when encoding a packet.

Encode a protocol header. Returns a bytearray which contains the header.

payload is the rest of the packet which will immediately follow this header.

prev is a packet_base.PacketBase subclass for the outer protocol header. prev is None if the current header is the outer-most. For example, prev is ipv4 or ipv6 for tcp.serialize.

class os_ken.lib.packet.dhcp.option(tag, value, length=0)

DHCP (RFC 2132) options encoder/decoder class.

This is used with os_ken.lib.packet.dhcp.dhcp.options.

An instance has the following attributes at least. Most of them are same to the on-wire counterparts but in host byte order. __init__ takes the corresponding args in this order.

Attribute

Description

tag

Option type. (except for the 'magic cookie', 'pad option' and 'end option'.)

value

Option's value. (set the value that has been converted to hexadecimal.)

length

Option's value length. (calculated automatically from the length of value.)
class os_ken.lib.packet.dhcp.options(option_list=None, options_len=0, magic_cookie='99.130.83.99')

DHCP (RFC 2132) options encoder/decoder class.

This is used with os_ken.lib.packet.dhcp.dhcp.

An instance has the following attributes at least. Most of them are same to the on-wire counterparts but in host byte order. __init__ takes the corresponding args in this order.

Attribute

Description

option_list

'end option' and 'pad option' are added automatically after the option class is stored in array.

options_len

Option's byte length. ('magic cookie', 'end option' and 'pad option' length including.)

magic_cookie

The first four octets contain the decimal values 99, 130, 83 and 99.