address
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... hosts allocate network addresses and deliver configuration parameters
to dynamically configured hosts ...
... hardware, values for those parameters
cannot be guessed or assumed to have correct defaults. Also,
distributed address allocation schemes depend on a polling/defense
mechanism for discovery of addresses ...
... address allocation schemes depend on a polling/defense
mechanism for discovery of addresses that are already in use. IP
hosts ...
... hosts may not always be able to defend their network addresses, so
that such a distributed address allocation scheme cannot be
...
... network addresses, so
that such a distributed address allocation scheme cannot be
guaranteed to avoid allocation of duplicate network addresses ...
... address allocation scheme cannot be
guaranteed to avoid allocation of duplicate network addresses.
...
...
DHCP supports three mechanisms for IP address allocation. In
"automatic allocation", DHCP assigns a permanent IP address ...
... IP address allocation. In
"automatic allocation", DHCP assigns a permanent IP address to a
client. In "dynamic allocation", DHCP ...
... client. In "dynamic allocation", DHCP assigns an IP address to a
client for a limited period of time (or until the client ...
... client for a limited period of time (or until the client explicitly
relinquishes the address). In "manual allocation", a client's IP
address is assigned by the network administrator, and DHCP ...
... client explicitly
relinquishes the address). In "manual allocation", a client's IP
address is assigned by the network administrator, and DHCP is used
...
... network administrator, and DHCP is used
simply to convey the assigned address to the client. A particular
network ...
...
Dynamic allocation is the only one of the three mechanisms that
allows automatic reuse of an address that is no longer needed by the
client to which it was assigned. Thus, dynamic allocation is
particularly useful for assigning an address ...
... address that is no longer needed by the
client to which it was assigned. Thus, dynamic allocation is
particularly useful for assigning an address to a client that will be
connected to the network ...
... connected to the network only temporarily or for sharing a limited
pool of IP addresses among a group of clients that do not need
...
... group of clients that do not need
permanent IP addresses. Dynamic allocation may also be a good choice
for assigning an IP address to a new client ...
... permanent IP addresses. Dynamic allocation may also be a good choice
for assigning an IP address to a new client being permanently
connected to a network ...
... new client being permanently
connected to a network where IP addresses are sufficiently scarce
that it is important to reclaim them when old clients are retired.
...
... DHCP to be used to eliminate the error-prone
process of manually configuring hosts with IP addresses in
environments where (for whatever reasons) it is desirable to manage
IP address ...
... IP addresses in
environments where (for whatever reasons) it is desirable to manage
IP address assignment outside of the DHCP mechanisms.
...
... There are several Internet protocols and related mechanisms that
address some parts of the dynamic host configuration problem. The
Reverse Address Resolution Protocol ...
... address some parts of the dynamic host configuration problem. The
Reverse Address Resolution Protocol (RARP) [10] (through the
...
... RARP (DRARP) [5]) explicitly
addresses the problem of network address discovery, and includes an
...
... addresses the problem of network address discovery, and includes an
automatic IP address assignment mechanism. The Trivial File Transfer
Protocol ...
... network address discovery, and includes an
automatic IP address assignment mechanism. The Trivial File Transfer
Protocol (TFTP) [20 ...
... configuration parameters. Morgan has
proposed extensions to BOOTP for dynamic IP address assignment [15].
The Network ...
... Network Information Protocol (NIP), used by the Athena project at
MIT, is a distributed mechanism for dynamic IP address assignment
[19]. The Resource Location Protocol ...
... internet
path [14]. The Address Resolution Protocol (ARP) has been proposed
as a transport protocol ...
... IP protocol. DHCP also does
not address registration of newly configured clients with the Domain
Name System ...
... binding is a collection of configuration parameters, including
at least an IP address, associated with or "bound to" a DHCP
client. Bindings are managed by DHCP servers ...
... Guarantee that any specific network address will not be in
use by more than one DHCP client at a time,
...
... clients can be assigned a
network address for a finite lease, allowing for serial reassignment
of network addresses ...
... address for a finite lease, allowing for serial reassignment
of network addresses to different clients. Second, DHCP provides the
...
... the overloading of the 'chaddr' field in BOOTP messages, where
'chaddr' is used both as a hardware address for transmission of BOOTP
reply messages ...
... by the server; for example,
the 'client identifier' may contain a hardware address, identical to
the contents of the 'chaddr' field, or it may contain another type of
identifier ...
... DHCP clarifies the interpretation of the 'siaddr' field as the
address of the server to use in the next step of the client's
bootstrap ...
... bootstrap process. A DHCP server may return its own address in the
'siaddr' field, if the server is prepared to supply the next
bootstrap ...
... message type.
1 = BOOTREQUEST, 2 = BOOTREPLY
htype 1 Hardware address type, see ARP section in "Assigned
Numbers" RFC; e.g., '1' = 10mb ethernet ...
... Numbers" RFC; e.g., '1' = 10mb ethernet.
hlen 1 Hardware address length (e.g. '6' for 10mb
ethernet).
...
... client, seconds elapsed since client
began address acquisition or renewal process.
flags 2 Flags (see figure 2).
ciaddr 4 Client ...
... flags 2 Flags (see figure 2).
ciaddr 4 Client IP address; only filled in if client is in
BOUND, RENEW or REBINDING state ...
... ARP requests.
yiaddr 4 'your' (client) IP address.
siaddr 4 IP address of next server to use in bootstrap ...
... client) IP address.
siaddr 4 IP address of next server to use in bootstrap;
returned in DHCPOFFER ...
... relay agent.
chaddr 16 Client hardware address.
sname 64 Optional server host name, null terminated string.
...
... IP packets delivered to the client's
hardware address before the IP address is configured; DHCP servers
...
... address) (note that the "hardware-address" should be typed by the
type of hardware to accommodate possible duplication of hardware
addresses ...
... address" should be typed by the
type of hardware to accommodate possible duplication of hardware
addresses resulting from bit-ordering problems in a mixed-media,
bridged ...
... bridged network) allowing for serial or concurrent reuse of a
hardware address on different subnets, and for hardware addresses
...
... hardware address on different subnets, and for hardware addresses
that may not be globally unique. Alternately, the key might be the
pair (IP ...
... DHCP client that has been moved to a
different subnet or has changed hardware addresses (perhaps because
the network interface failed and was replaced). The protocol defines
...
... permanent network (IP) addresses to clients. The basic mechanism for
the dynamic allocation of network ...
... clients. The basic mechanism for
the dynamic allocation of network addresses is simple: a client
requests the use of an address for some period of time. The
...
... network addresses is simple: a client
requests the use of an address for some period of time. The
allocation mechanism (the collection of DHCP servers) guarantees not
...
... allocation mechanism (the collection of DHCP servers) guarantees not
to reallocate that address within the requested time and attempts to
return the same network address ...
... address within the requested time and attempts to
return the same network address each time the client requests an
address ...
... address each time the client requests an
address. In this document, the period over which a network address
...
... address. In this document, the period over which a network address
is allocated to a client is referred to as a "lease" [11 ...
... client may extend its lease with subsequent requests. The client may
issue a message to release the address back to the server when the
client no longer needs the address ...
... address back to the server when the
client no longer needs the address. The client may ask for a
permanent assignment by asking for an infinite lease. Even when
...
... client may ask for a
permanent assignment by asking for an infinite lease. Even when
assigning "permanent" addresses, a server may choose to give out
lengthy but non-infinite leases to allow detection of the fact that
the client ...
... In some environments it will be necessary to reassign network
addresses due to exhaustion of available addresses. In such
environments, the allocation mechanism will reuse addresses ...
... network
addresses due to exhaustion of available addresses. In such
environments, the allocation mechanism will reuse addresses whose
...
... addresses due to exhaustion of available addresses. In such
environments, the allocation mechanism will reuse addresses whose
lease has expired. The server should use whatever information is
available in the configuration information ...
... available in the configuration information repository to choose an
address to reuse. For example, the server may choose the least
recently assigned address. As a consistency ...
... address to reuse. For example, the server may choose the least
recently assigned address. As a consistency check, the allocating
server SHOULD probe ...
... consistency check, the allocating
server SHOULD probe the reused address before allocating the address,
e.g., with an ICMP ...
... server SHOULD probe the reused address before allocating the address,
e.g., with an ICMP echo request ...
... client-server interaction. If the client already knows its
address, some steps may be omitted; this abbreviated interaction is
described in section 3.2.
...
... DHCPDISCOVER message MAY include options that suggest
values for the network address and lease duration. BOOTP relay
agents may pass the message on to DHCP servers ...
... DHCPOFFER message that includes an
available network address in the 'yiaddr' field (and other
configuration parameters in DHCP options ...
... DHCP options). Servers need not
reserve the offered network address, although the protocol will
work more efficiently if the server avoids allocating the offered
network ...
... work more efficiently if the server avoids allocating the offered
network address to another client. When allocating a new address,
...
... network address to another client. When allocating a new address,
servers SHOULD check that the offered network address ...
... address,
servers SHOULD check that the offered network address is not
already in use; e.g., the server may probe the offered address ...
... address is not
already in use; e.g., the server may probe the offered address
with an ICMP Echo Request ...
... network administrators MAY choose to disable probes of newly
allocated addresses. The server transmits the DHCPOFFER message
to the client ...
... offered parameters from one server and implicitly
declining offers from all others, (b) confirming
correctness of previously allocated address after,
e.g., system reboot, or (c) extending the lease on a
particular network ...
... DHCPRELEASE - Client to server relinquishing network address and
cancelling remaining lease.
...
... Timeline diagram of messages exchanged between DHCP
client and servers when allocating a new network address
3. The client ...
... identifier' option to indicate which
server it has selected, and that MAY include other options
specifying desired configuration values. The 'requested IP
address' option MUST be set to the value of 'yiaddr' in the
DHCPOFFER message from the server. This DHCPREQUEST ...
... client identifier' or
'chaddr' and assigned network address constitute a unique
identifier for the client's lease and are used by both the client
and server ...
... client is responding. The server SHOULD NOT check the offered
network address at this point. The 'yiaddr' field in the DHCPACK
messages is filled in with the selected network address ...
... address at this point. The 'yiaddr' field in the DHCPACK
messages is filled in with the selected network address.
If the selected server is unable to satisfy the DHCPREQUEST ...
... DHCPREQUEST message
(e.g., the requested network address has been allocated), the
server SHOULD respond with a DHCPNAK message.
...
... DHCPOFFER messages as unavailable. The server SHOULD mark an
address offered to a client in a DHCPOFFER message as available if
...
... parameters (e.g., ARP for allocated network address), and notes the
duration of the lease specified in the DHCPACK message. At this
...
... client is configured. If the client detects that the
address is already in use (e.g., through the use of ARP), the
client ...
... 6. The client may choose to relinquish its lease on a network address
by sending a DHCPRELEASE message to the server. The client
...
... client identifier',
or 'chaddr' and network address in the DHCPRELEASE message. If the
client used a 'client identifier ...
... client remembers and wishes to reuse a previously allocated
network address, a client may choose to omit some of the steps
described in the previous section. The timeline ...
... The message includes the client's network address in the
'requested IP address' option. As the client ...
... network address in the
'requested IP address' option. As the client has not received its
network ...
... client has not received its
network address, it MUST NOT fill in the 'ciaddr' field. BOOTP
relay agents ...
... client used a 'client identifier' to obtain its
address, the client MUST use the same 'client identifier' in the
...
... broadcast the DHCPNAK message to the 0xffffffff broadcast address
because the client may not have a correct network ...
... ARP requests.
Otherwise, the server MUST send the DHCPNAK message to the IP
address of the BOOTP relay agent, as recorded in 'giaddr'. The
...
... relay agent will, in turn, forward the message directly to the
client's hardware address, so that the DHCPNAK can be delivered even
if the client ...
... by the 'client identifier' or 'chaddr' and the network address. At
this point, the client is configured.
...
...
If the client detects that the IP address in the DHCPACK message
is already in use, the client ...
... restarts the configuration process by requesting a
new network address. This action corresponds to the client
moving to the INIT ...
... DHCPNAK message, it cannot reuse its
remembered network address. It must instead request a new
address by restarting ...
... network address. It must instead request a new
address by restarting the configuration process, this time
using the (non-abbreviated) procedure described in section
...
... client MAY choose to use the
previously allocated network address and configuration parameters
for the remainder of the unexpired lease. This corresponds to
...
... client may choose to relinquish its lease on a network
address by sending a DHCPRELEASE message to the server. The
client identifies the lease to be released with its
...
... client retains its network
address locally, the client will not normally relinquish its
lease during a graceful shutdown. Only in the case where the
...
... A client acquires a lease for a network address for a fixed period of
time (which may be infinite). Throughout the protocol, times are to
be represented in units of seconds. The time value of 0xffffffff is
...
... If a client has obtained a network address through some other means
(e.g., manual configuration), it may use a DHCPINFORM ...
... configuration parameters appropriate for the client without:
allocating a new address, checking for an existing binding, filling
in 'yiaddr' or including lease time parameters. The servers SHOULD
...
... unicast the DHCPACK reply to the address given in the 'ciaddr' field
of the DHCPINFORM message.
...
... In addition, the client may suggest values for the network address
and lease time in the DHCPDISCOVER message. The client ...
... DHCPDISCOVER message. The client may include
the 'requested IP address' option to suggest that a particular IP
address be assigned, and may include the 'IP address lease time'
...
... client may include
the 'requested IP address' option to suggest that a particular IP
address be assigned, and may include the 'IP address lease time'
option to suggest the lease time it would like. Other options
...
... the 'requested IP address' option to suggest that a particular IP
address be assigned, and may include the 'IP address lease time'
option to suggest the lease time it would like. Other options
representing "hints ...
... DHCPREQUEST message. However, additional options may
be ignored by servers, and multiple servers may, therefore, not
return identical values for some options. The 'requested IP address'
option is to be filled in only in a DHCPREQUEST message when the
...
... client fills in the 'ciaddr' field only when correctly configured
with an IP address in BOUND, RENEWING or REBINDING state.
...
... If a server receives a DHCPREQUEST message with an invalid 'requested
IP address', the server SHOULD respond to the client with a DHCPNAK
...
... A client SHOULD use DHCP to reacquire or verify its IP address and
network parameters whenever the local network ...
... If a client has knowledge of a previous network address and is unable
to contact a local DHCP server, the client ...
... client may continue to use the
previous network address until the lease for that address expires.
If the lease expires before the client ...
... previous network address until the lease for that address expires.
If the lease expires before the client can contact a DHCP server ...
... client must immediately discontinue use of the previous network
address and may inform local users of the problem.
...
... DHCP server has a block of network
addresses from which it can satisfy requests for new addresses. Each
server also maintains a database ...
... network
addresses from which it can satisfy requests for new addresses. Each
server also maintains a database of allocated addresses ...
... addresses. Each
server also maintains a database of allocated addresses and leases in
local permanent storage.
...
... port
(68). A server with multiple network address (e.g., a multi-homed
host) MAY use any of its network addresses ...
... address (e.g., a multi-homed
host) MAY use any of its network addresses in outgoing DHCP messages.
...
... DHCP server
in a DHCP message and as a destination address from clients to
servers. A server with multiple network ...
... clients to
servers. A server with multiple network addresses MUST be prepared
to to accept any of its network addresses ...
... addresses MUST be prepared
to to accept any of its network addresses as identifying that server
in a DHCP message. To accommodate potentially incomplete network ...
... DHCP message. To accommodate potentially incomplete network
connectivity, a server MUST choose an address as a 'server
identifier' that, to the best of the server's knowledge, is reachable
...
... subnet (i.e., the 'giaddr' field in the
message from the client is zero), the server SHOULD select the IP
address the server is using for communication on that subnet as the
'server identifier ...
... subnet as the
'server identifier'. If the server is using multiple IP addresses on
that subnet, any such address ...
... IP addresses on
that subnet, any such address may be used. If the server has
received a message through a DHCP relay agent, the server SHOULD
...
... received a message through a DHCP relay agent, the server SHOULD
choose an address from the interface on which the message was
recieved as the 'server identifier ...
... better information on which to make its choice). DHCP clients MUST
use the IP address provided in the 'server identifier' option for any
unicast ...
... client prior to that client obtaining
its IP address must have the source address field in the IP header
...
... client obtaining
its IP address must have the source address field in the IP header
set to 0.
...
... BOOTP relay agent whose address appears in 'giaddr'. If the 'giaddr'
field is zero and the 'ciaddr' field is nonzero, then the server
unicasts ...
... unicasts DHCPOFFER and DHCPACK messages to the address in 'ciaddr'.
If 'giaddr' is zero and 'ciaddr' is zero, and the broadcast bit ...
... DHCPOFFER and DHCPACK
messages to the client's hardware address and 'yiaddr' address. In
all cases, when 'giaddr' is zero, the server broadcasts ...
... DHCPACK
messages to the client's hardware address and 'yiaddr' address. In
all cases, when 'giaddr' is zero, the server broadcasts any DHCPNAK ...
... IP header) is
set to the DHCP 'yiaddr' address and the link-layer destination
address is set to the DHCP ...
... DHCP 'yiaddr' address and the link-layer destination
address is set to the DHCP 'chaddr' address. Unfortunately, some
...
... link-layer destination
address is set to the DHCP 'chaddr' address. Unfortunately, some
client implementations are unable to receive such unicast ...
... IP
datagrams until the implementation has been configured with a valid
IP address (leading to a deadlock in which the client's IP address
cannot be delivered until the client ...
... valid
IP address (leading to a deadlock in which the client's IP address
cannot be delivered until the client has been configured with an IP
address ...
... client's IP address
cannot be delivered until the client has been configured with an IP
address).
...
... unicast IP datagrams until its protocol
software has been configured with an IP address SHOULD set the
BROADCAST bit ...
... broadcast using an IP broadcast address (preferably 0xffffffff)
as the IP destination address ...
... address (preferably 0xffffffff)
as the IP destination address and the link-layer broadcast address ...
... destination address and the link-layer broadcast address as
the link-layer destination address ...
... bit is cleared
to 0, the message SHOULD be sent as an IP unicast to the IP address
specified in the 'yiaddr' field and the link-layer address specified
...
... IP unicast to the IP address
specified in the 'yiaddr' field and the link-layer address specified
in the 'chaddr' field. If unicasting is not possible, the message
MAY be sent as an IP ...
... broadcast using an IP broadcast address
(preferably 0xffffffff) as the IP destination address ...
... avoid unexpected changes in a clients network address due to transfer
of hardware interfaces ...
... a DNS name as the 'client identifier', causing address leases to be
associated with the DNS name rather than a specific hardware ...
... address for the requesting client. If no
address is available, the server may choose to report the problem to
the system administrator. If an address ...
... address is available, the server may choose to report the problem to
the system administrator. If an address is available, the new address
SHOULD be chosen as follows:
...
... the system administrator. If an address is available, the new address
SHOULD be chosen as follows:
...
... client's (now
expired or released) binding, if that address is in the server's
pool of available addresses and not already allocated, ELSE
...
... binding, if that address is in the server's
pool of available addresses and not already allocated, ELSE
...
... address requested in the 'Requested IP Address' option, if that
address is valid and not already allocated, ELSE
...
... A new address allocated from the server's pool of available
addresses; the address is selected based on the subnet from which
...
... address allocated from the server's pool of available
addresses; the address is selected based on the subnet from which
the message was received (if 'giaddr' is 0) or on the address ...
... address is selected based on the subnet from which
the message was received (if 'giaddr' is 0) or on the address of
the relay agent that forwarded the message ('giaddr' when not 0).
...
...
As described in section 4.2, a server MAY, for administrative
reasons, assign an address other than the one requested, or may
refuse to allocate an address to a particular client ...
... reasons, assign an address other than the one requested, or may
refuse to allocate an address to a particular client even though free
addresses ...
... segment), it may be
the case that the DHCP client should be assigned an address from a
different subnet than the address ...
... address from a
different subnet than the address recorded in 'giaddr'. Thus, DHCP
does not require that the client ...
... DHCP
does not require that the client be assigned as address from the
subnet in 'giaddr'. A server is free to choose some other subnet ...
... and it is beyond the scope of the DHCP specification to describe ways
in which the assigned IP address might be chosen.
...
... DHCP, the server SHOULD
NOT reuse the selected network address before the client responds to
the server's DHCPOFFER ...
... the server's DHCPOFFER message. The server may choose to record the
address as offered to the client.
...
... client already has an assigned network
address, the server returns the lease expiration time previously
assigned to that address (note that the client ...
... address, the server returns the lease expiration time previously
assigned to that address (note that the client must explicitly
request a specific lease to extend the expiration time on a
...
... client must explicitly
request a specific lease to extend the expiration time on a
previously assigned address), ELSE
...
... client does not have an assigned
network address, the server assigns a locally configured default
lease time, ELSE
...
... client has an assigned network
address), the server may choose either to return the requested
lease (if the lease is acceptable to local policy) or select
another lease.
...
... 'op' BOOTREPLY BOOTREPLY BOOTREPLY
'htype' (From "Assigned Numbers" RFC)
'hlen' (Hardware address length in octets)
'hops' 0 0 0
'xid' 'xid' from client ...
... DHCPNAK
------ --------- ------- -------
Requested IP address MUST NOT MUST NOT MUST NOT
IP address lease time MUST MUST (DHCPREQUEST) MUST NOT
...
... ------ --------- ------- -------
Requested IP address MUST NOT MUST NOT MUST NOT
IP address lease time MUST MUST (DHCPREQUEST) MUST NOT
MUST NOT (DHCPINFORM ...
...
Once the network address and lease have been determined, the server
constructs a DHCPOFFER message with the offered configuration
parameters ...
... parameters (with the possible exception of a newly allocated network
address) to ensure predictable client behavior regardless of which
server the client ...
... DHCPOFFER message from a server, from a client verifying a previously
allocated IP address or from a client extending the lease on a
network ...
... client extending the lease on a
network address. If the DHCPREQUEST message contains a 'server
identifier ...
...
Client inserts the address of the selected server in 'server
identifier', 'ciaddr' MUST be zero, 'requested IP address ...
... address of the selected server in 'server
identifier', 'ciaddr' MUST be zero, 'requested IP address' MUST be
filled in with the yiaddr value from the chosen DHCPOFFER.
...
... client has accepted the offer. Because
the servers have not committed any network address assignments on
the basis of a DHCPOFFER, servers are free to reuse offered
...
... DHCPOFFER, servers are free to reuse offered
network addresses in response to subsequent requests. As an
implementation detail, servers SHOULD NOT reuse offered addresses
...
... network addresses in response to subsequent requests. As an
implementation detail, servers SHOULD NOT reuse offered addresses
and may use an implementation-specific timeout mechanism to decide
when to reuse an offered address ...
... addresses
and may use an implementation-specific timeout mechanism to decide
when to reuse an offered address.
o DHCPREQUEST ...
...
'server identifier' MUST NOT be filled in, 'requested IP address'
option MUST be filled in with client's notion of its previously
...
... option MUST be filled in with client's notion of its previously
assigned address. 'ciaddr' MUST be zero. The client is seeking to
verify a previously allocated, cached configuration. Server SHOULD
...
... send a DHCPNAK message to the client if the 'requested IP address'
is incorrect, or is on the wrong network.
...
... correct network is done by examining the contents of 'giaddr', the
'requested IP address' option, and a database lookup. If the DHCP
server detects that the client ...
... subnet mask or remote subnet mask (if
'giaddr' is not zero) to 'requested IP address' option value
doesn't match reality), then the server SHOULD send a DHCPNAK
...
... DHCP server should check if
the client's notion of its IP address is correct. If not, then the
server SHOULD send a DHCPNAK message to the client ...
... DHCPNAK message to the 0xffffffff broadcast address because the
client may not have a correct network ...
... client, because the client may not have a correct network address
or subnet mask, and the client ...
...
'server identifier' MUST NOT be filled in, 'requested IP address'
option MUST NOT be filled in, 'ciaddr' MUST be filled in with
client's IP address ...
... IP address'
option MUST NOT be filled in, 'ciaddr' MUST be filled in with
client's IP address. In this situation, the client is completely
configured, and is trying to extend its lease. This message will
...
...
'server identifier' MUST NOT be filled in, 'requested IP address'
option MUST NOT be filled in, 'ciaddr' MUST be filled in with
client's IP address ...
... IP address'
option MUST NOT be filled in, 'ciaddr' MUST be filled in with
client's IP address. In this situation, the client is completely
configured, and is trying to extend its lease. This message MUST
...
... broadcast to the 0xffffffff IP broadcast address. The DHCP
server SHOULD check 'ciaddr' for correctness before replying to
the DHCPREQUEST ...
... discovered through some other means that the suggested network
address is already in use. The server MUST mark the network address
...
... address is already in use. The server MUST mark the network address
as not available and SHOULD notify the local system administrator ...
... Upon receipt of a DHCPRELEASE message, the server marks the network
address as not allocated. The server SHOULD retain a record of the
client ...
... The server responds to a DHCPINFORM message by sending a DHCPACK
message directly to the address given in the 'ciaddr' field of the
DHCPINFORM message. The server MUST NOT send a lease expiration time
...
... |server-ip |MUST NOT |MUST |MUST NOT |MUST NOT |
|requested-ip |MUST |MUST |MUST NOT |MUST NOT |
|ciaddr |zero |zero |IP address |IP address|
---------------------------------------------------------------------
...
... |requested-ip |MUST |MUST |MUST NOT |MUST NOT |
|ciaddr |zero |zero |IP address |IP address|
---------------------------------------------------------------------
...
... client MAY
suggest a network address and/or lease time by including the
'requested IP address' and 'IP address ...
... network address and/or lease time by including the
'requested IP address' and 'IP address lease time' options. The
client ...
... address and/or lease time by including the
'requested IP address' and 'IP address lease time' options. The
client MUST include its hardware address ...
... IP address lease time' options. The
client MUST include its hardware address in the 'chaddr' field, if
necessary for delivery of DHCP ...
... DHCPOFFER message or the DHCPOFFER message
from the previously used server) and extracts the server address from
the 'server identifier' option in the DHCPOFFER ...
... 'op' BOOTREQUEST BOOTREQUEST BOOTREQUEST
'htype' (From "Assigned Numbers" RFC)
'hlen' (Hardware address length in octets)
'hops' 0 0 0
'xid' selected by client ...
... client's hardware
address address address
'sname' options, if options, if (unused)
indicated in indicated in
...
... DHCPINFORM DHCPRELEASE
------ ------------ ----------- -----------
Requested IP address MAY MUST (in MUST
(DISCOVER) SELECTING or (DHCPDECLINE),
...
... (INFORM) MUST NOT (in (DHCPRELEASE)
BOUND or
RENEWING)
IP address lease time MAY MAY MUST NOT
(DISCOVER)
MUST NOT
...
...
If the parameters are acceptable, the client records the address of
the server that supplied the parameters from the 'server identifier'
...
... the server that supplied the parameters from the 'server identifier'
field and sends that address in the 'server identifier' field of a
DHCPREQUEST ...
... DHCPACK message. The client SHOULD perform a
check on the suggested address to ensure that the address is not
already in use. For example, if the client ...
... client SHOULD perform a
check on the suggested address to ensure that the address is not
already in use. For example, if the client is on a network ...
... request. When broadcasting an ARP request for the suggested address,
the client must fill in its own hardware address ...
... hardware address as the sender's
hardware address, and 0 as the sender's IP address, to avoid
...
... subnet. If the
network address appears to be in use, the client MUST send a
DHCPDECLINE message ...
... ARP
reply to announce the client's new IP address and clear any outdated
ARP cache entries in hosts ...
... message. The client MUST insert its known network address as a
'requested IP address' option in the DHCPREQUEST ...
... client places its own network address in the 'ciaddr' field. The
client SHOULD NOT request lease time parameters.
...
... DHCPINFORM to the DHCP server if it
knows the server's address, otherwise it broadcasts the message to
the limited (all 1s) broadcast ...
... broadcasts the message to
the limited (all 1s) broadcast address. DHCPINFORM messages MUST be
directed to the 'DHCP server ...
... unicasts DHCPRELEASE messages to the server. Because the
client is declining the use of the IP address supplied by the server,
the client ...
... DHCP server. If the client receives no response to DHCP
messages sent to the IP address of a known DHCP server, the DHCP
client reverts to using the IP ...
... which the client tries to extend its lease on its network address.
T1 is the time at which the client ...
... DHCPREQUEST to its current network
address. The client records the local time at which the DHCPREQUEST
...
... client has successfully reacquired its
network address, returns to BOUND state and may continue network
...
... DHCPREQUEST to its
current network address. The client MUST NOT include a 'server
identifier ...
... client is given a new
network address, it MUST NOT continue using the previous network
address ...
... address, it MUST NOT continue using the previous network
address and SHOULD notify the local users of the problem.
...
... If the client no longer requires use of its assigned network address
(e.g., the client is gracefully shut down), the client ...
... Brownell, D, "Dynamic Reverse Address Resolution Protocol (DRARP)", Work in Progress. ...
... Finlayson, R., Mann, T., Mogul, J., and M. Theimer, "A Reverse Address Resolution Protocol", RFC 903std38, Stanford, June 1984. ...
... Jeffrey Schiller and Mark Rosenstein. A Protocol for the Dynamic Assignment of IP Addresses for use on an Ethernet. (Available from the Athena Project, MIT), 1989. ...
... then send false and potentially disruptive information to clients
such as incorrect or duplicate IP addresses, incorrect routing
information (including spoof routers, etc.), incorrect domain ...
... domain
nameserver addresses (such as spoof nameservers), and so on.
Clearly, once this seed information is in place, an attacker ...
... Author's Address ...
... MTU on/off HRC 3.3.3
Broadcast address flavor 0x00000000/0xffffffff HRC 3.3.6
Perform mask discovery on/off HRC 3.2.2.9
Be a mask supplier on/off HRC 3.2.2.9
...
... integer HRC 3.3.1.2
first-hop router (address) HRC 3.3.1.2
ignore redirects on/off HRC 3.3.1.2
PMTU ...