DHCP¶
DHCP packet parser/serializer
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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).
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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.
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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.
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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.)
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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.