address
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... A host is said to be multihomed if it has multiple IP
addresses. For a discussion of multihoming, see Section
...
... physical interface to a connected network and
has a (possibly unique) link-layer address. Multiple
physical network interfaces ...
... same link-layer address, but the address must be unique
for different hosts on the same physical ...
... network] interface to be a logical
path, distinguished by a unique IP address, to a connected
network. See Section 3.3.4. ...
... Specific-destination address ...
... is performed at the time that ARP is used to discover the
link-layer address of a destination system.
...
... ARP request for its IP protocol address would send a
trailer ARP reply in addition to the normal IP ...
... IP ARP reply answers an
outstanding request; this is true when the hardware
address for the host is still unknown when the IP ARP ...
... Address Resolution Protocol -- ARP ...
... flooding (repeatedly sending an
ARP Request for the same IP address, at a high rate) MUST be
included. The recommended maximum rate is 1 per second per
...
... cache entry is
"refreshed" (by observing the source fields,
regardless of target address, of an ARP broadcast
...
... link layer SHOULD save (rather than discard) at least
one (the latest) packet of each set of packets destined to
the same unresolved IP address, and transmit the saved
packet when the address has been resolved.
...
... the same unresolved IP address, and transmit the saved
packet when the address has been resolved.
...
...
Address translation from Internet addresses to link-layer
addresses on Ethernet and IEEE 802 networks ...
... Address translation from Internet addresses to link-layer
addresses on Ethernet and IEEE 802 networks MUST be managed by
...
...
Although the IP layer does not generally know link layer
addresses (since every different network medium typically has
a different address format ...
... link layer
addresses (since every different network medium typically has
a different address format), the broadcast address on a
...
... a different address format), the broadcast address on a
broadcast-capable medium is an important special case. See
...
...
A host is said to be multihomed if it has multiple IP addresses.
Multihoming introduces considerable confusion and complexity into
...
... group of hosts, and may be either
permanent or transient. Permanent multicast addresses are
allocated by the Internet Assigned Number Authority
...
... Internet Assigned Number Authority
[INTRO:6], while transient addresses may be allocated
dynamically to transient groups. Group ...
... We now summarize the important special cases for Class A, B,
and C IP addresses, using the following notation for an IP
address:
...
... This notation is not intended to imply that the 1-bits in an
address mask need be contiguous.
...
... host on this network. MUST NOT be sent, except as
a source address as part of an initialization procedure
by which the host ...
... initialization procedure
by which the host learns its own IP address.
See also Section 3.3.6 for a non-standard use of {0,0}.
...
... host on this network. It MUST NOT be sent,
except as a source address as part of an initialization
procedure by which the host ...
...
A datagram with this destination address will be
received by every host on the connected physical ...
... subnets of the specified
subnetted network. It MUST NOT be used as a source
address.
(g) { 127, <any> }
...
...
IP addresses are not permitted to have the value 0 or -1 for
any of the <Host-number>, <Network ...
... IP [IP:3]. As
a result, there will be an address mask of the form:
{-1, -1, 0} associated with each of the host's local IP
addresses ...
... address mask of the form:
{-1, -1, 0} associated with each of the host's local IP
addresses; see Sections 3.2.2.9 and 3.3.1.1.
...
... When a host sends any datagram, the IP source address MUST
be one of its own IP addresses (but not a broadcast ...
... datagram, the IP source address MUST
be one of its own IP addresses (but not a broadcast or
multicast address ...
... (one of) the host's IP address(es); or ...
... destination is processed as if it had been
addressed to one of the host's IP addresses; we use the term
"specific-destination address" for the equivalent local IP
address ...
... host's IP addresses; we use the term
"specific-destination address" for the equivalent local IP
address of the host. The specific-destination address ...
... IP addresses; we use the term
"specific-destination address" for the equivalent local IP
address of the host. The specific-destination address is
...
... destination address" for the equivalent local IP
address of the host. The specific-destination address is
defined to be the destination address in the IP header ...
... host. The specific-destination address is
defined to be the destination address in the IP header
unless the header ...
... unless the header contains a broadcast or multicast address,
in which case the specific-destination is an IP address ...
... multicast address,
in which case the specific-destination is an IP address
assigned to the physical interface on which the datagram ...
... silently discard an incoming datagram containing
an IP source address that is invalid by the rules of this
section. This validation could be done in either the IP
layer ...
... Internet hosts was to allow
IP addresses to be featureless 32-bit numbers, avoiding
algorithms ...
... 32-bit numbers, avoiding
algorithms that required a knowledge of the IP address
format. Otherwise, any future change in the format or
interpretation of IP addresses ...
... IP address
format. Otherwise, any future change in the format or
interpretation of IP addresses will require host
software changes. However, validation ...
... validation of broadcast and
multicast addresses violates this goal; a few other
violations are described elsewhere in this document.
...
... option: {G1, G2, ... Gn >>}, with S and D as the
IP source and destination addresses. If (B) were
sent, the datagram received at D would again
...
... contain S and D as the same IP source and
destination addresses, but the option would be:
{S, G1, ...Gn >>}; i.e., the originating host
...
... timestamp in a
Timestamp option whose Internet address fields are
not pre-specified or whose first pre-specified
address ...
... Internet address fields are
not pre-specified or whose first pre-specified
address is the host's interface address ...
... Redirect message SHOULD be silently discarded if the new
gateway address it specifies is not on the same connected
(sub-) net through which the Redirect arrived [INTRO:2,
Appendix A], or if the source of the Redirect is not the
...
... Echo to a broadcast
address provides a valuable diagnostic capability and
those who feel that misuse of this feature can too
easily create ...
... ICMP Echo Reply MUST be the same
as the specific-destination address (defined in Section
3.2.1.3) of the corresponding ICMP Echo Request message ...
... host MUST support the first, and MAY implement all three,
of the following methods for determining the address mask(s)
corresponding to its IP address(es):
...
... obtaining the address mask(s) dynamically as a side-
effect of the system initialization process (see
...
... (a) When it initializes, the host MUST broadcast an Address
Mask Request message on the connected network ...
... Request message on the connected network
corresponding to the IP address. It MUST retransmit
this message a small number of times if it does not
receive an immediate Address ...
... IP address. It MUST retransmit
this message a small number of times if it does not
receive an immediate Address Mask Reply.
(b) Until it has received an Address ...
... Address Mask Reply.
(b) Until it has received an Address Mask Reply, the host
SHOULD assume a mask appropriate for the address ...
... Address Mask Reply, the host
SHOULD assume a mask appropriate for the address class
of the IP address ...
... network is not subnetted.
(c) The first Address Mask Reply message received MUST be
used to set the address ...
... Address Mask Reply message received MUST be
used to set the address mask corresponding to the
particular local IP address. This is true even if the
...
... used to set the address mask corresponding to the
particular local IP address. This is true even if the
first Address Mask Reply message ...
... particular local IP address. This is true even if the
first Address Mask Reply message is "unsolicited", in
which case it will have been broadcast ...
... broadcast and may arrive
after the host has ceased to retransmit Address Mask
Requests. Once the mask has been set by an Address
...
... host has ceased to retransmit Address Mask
Requests. Once the mask has been set by an Address
Mask Reply, later Address Mask Reply messages ...
... Requests. Once the mask has been set by an Address
Mask Reply, later Address Mask Reply messages MUST be
(silently) ignored.
...
... Address Mask messages are disabled, then no
ICMP Address Mask Requests will be sent, and any ICMP
Address ...
... Address Mask Requests will be sent, and any ICMP
Address Mask Replies received for that local IP address MUST
be (silently) ignored.
...
...
A host SHOULD make some reasonableness check on any address
mask it installs; see IMPLEMENTATION section below.
...
...
A system MUST NOT send an Address Mask Reply unless it is an
authoritative agent for address ...
... Address Mask Reply unless it is an
authoritative agent for address masks. An authoritative
agent may be a host ...
... host or a gateway, but it MUST be explicitly
configured as a address mask agent. Receiving an address ...
... address mask agent. Receiving an address
mask via an Address Mask Reply does not give the receiver ...
...
With a statically configured address mask, there SHOULD be
an additional configuration flag that determines whether the
host ...
... host is to act as an authoritative agent for this mask,
i.e., whether it will answer Address Mask Request messages
using this mask.
...
... host MUST broadcast an
Address Mask Reply for the mask on the appropriate interface
when it initializes.
...
... Initialization" in [INTRO:1] for more
information about the use of Address Mask Request/Reply
messages.
...
...
Hosts that casually send Address Mask Replies with
invalid address masks have often been a serious
...
... Hosts that casually send Address Mask Replies with
invalid address masks have often been a serious
nuisance. To prevent this, Address Mask Replies ought
...
... invalid address masks have often been a serious
nuisance. To prevent this, Address Mask Replies ought
to be sent only by authoritative agents that have been
...
...
When an authoritative agent receives an Address Mask
Request message, it will send a unicast Address ...
... Address Mask
Request message, it will send a unicast Address Mask
Reply to the source IP address. If the network ...
... Request message, it will send a unicast Address Mask
Reply to the source IP address. If the network part of
this address ...
... source IP address. If the network part of
this address is zero (see (a) and (b) in 3.2.1.3), the
Reply will be broadcast.
...
... agent will broadcast an unsolicited
Address Mask Reply whenever it initializes, in order to
update the masks of all hosts ...
...
The following reasonableness check on an address mask
is suggested: the mask is not all 1 bits, and it is
...
... destination address bits extracted by the
address mask match the IP source address bits extracted
...
... bits extracted by the
address mask match the IP source address bits extracted
by the same mask, then the destination ...
...
A special-case destination address is handled as follows:
...
...
Since the subnet mask appropriate to the destination address
is generally not known, a Network Redirect message ...
... route cache entry for the destination host
address (and the destination is not on the connected
network ...
... Local IP address (for a multihomed host)
...
... Destination IP address
...
...
Field (2) MAY be the full IP address of the destination
host, or only the destination network ...
... route cache should
be keyed on destination host addresses alone, or allow
both host and network ...
... will generally result in entries keyed on
destination host addresses; the simplest and most
general scheme would be to use host addresses ...
... The use of only host addresses allows the
destination address to be used as a pure 32-bit
number ...
... host addresses allows the
destination address to be used as a pure 32-bit
number, which may allow the Internet architecture
...
... ARP mappings may
be used as negative advice for the corresponding
IP address.
...
... Packets arriving from a particular link-layer
address are evidence that the system at this
address is alive. However, turning this
...
... Packets arriving from a particular link-layer
address are evidence that the system at this
address is alive. However, turning this
information into advice about gateways requires
...
... information into advice about gateways requires
mapping the link-layer address into an IP address,
and then checking that IP address ...
... gateways requires
mapping the link-layer address into an IP address,
and then checking that IP address against the
...
... link-layer address into an IP address,
and then checking that IP address against the
gateways pointed to by the route cache ...
... IP address(es). ...
... Address mask(s). ...
... IP datagram size that may be sent, for a particular
combination of IP source and destination addresses and perhaps
TOS.
...
... and EMTU_S must be less than or equal to the MTU of the network
interface corresponding to the source address of the datagram.
Note that <IP header ...
... MTU along the path, the IP layer SHOULD use
EMTU_S <= 576 whenever the destination address is not on a
connected network, and otherwise use the connected network ...
... class mask, rather than the subnet
address mask, to be used to choose an EMTU_S. For a multihomed
host, an "All-Subnets ...
...
A multihomed host has multiple IP addresses, which we may
think of as "logical interfaces". These logical interfaces ...
...
When a host has multiple IP addresses that all have the
same <Network-number> part (and the same <Subnet ...
... transport protocol
instance ("entity") has no address of its own, but instead
uses a single Internet Protocol (IP ...
... and for the interfaces between them. In particular, the
application software may have to be aware of the multiple IP
addresses of a multihomed host; in other cases, the choice
can be made within the network ...
...
The following general rules apply to the selection of an IP
source address for sending a datagram from a multihomed
host ...
... datagram is sent in response to a received
datagram, the source address for the response SHOULD be
the specific-destination address of the request. See
...
... datagram, the source address for the response SHOULD be
the specific-destination address of the request. See
Sections 4.1.3.5 and 4.2.3.7 and the "General Issues"
section of [INTRO:1 ...
... higher layers.
Otherwise, a source address must be selected.
(2) An application MUST be able to explicitly specify the
...
...
(2) An application MUST be able to explicitly specify the
source address for initiating a connection or a
request.
...
...
(3) In the absence of such a specification, the networking
software MUST choose a source address. Rules for this
choice are described below.
...
... silently discard an incoming datagram whose
destination address does not correspond to the physical
interface through which it is received.
...
... routed) IP datagrams only through the physical
interface that corresponds to the IP source address of
the datagrams.
...
... physical interface that did not correspond to the
destination address.
...
...
Here the source address is included as a parameter
in order to select a gateway that is directly
...
... general there be at least one default gateway, and
preferably multiple defaults, for each IP source
address.
...
... datagram is sent out a physical
interface that does not correspond to the
destination address, the first-hop gateway will
not realize when it needs to send a Redirect. On
...
... Choosing a Source Address ...
... transport layer on a multihomed
host needs to know which source address to use. If the
application does not specify it, the transport layer
...
... TOS is the Type-of-Service value (see Section
3.2.1.6), and the result is the desired source address.
The following rules are suggested for implementing this
mapping:
...
...
(a) If the remote Internet address lies on one of the
(sub-) nets to which the host is directly
...
... (sub-) nets to which the host is directly
connected, a corresponding source address may be
chosen, unless the corresponding interface is
...
... network through any network interface; if so, a
local IP address corresponding to that interface
may be chosen.
...
... A source-routed datagram being forwarded MAY (and normally
will) have a source address that is not one of the IP
addresses of the forwarding host.
...
... datagram being forwarded MAY (and normally
will) have a source address that is not one of the IP
addresses of the forwarding host.
...
...
A host MUST recognize any of these forms in the destination
address of an incoming datagram.
...
... hosts* that use non-standard broadcast
address forms, substituting 0 for -1. All hosts SHOULD
recognize and accept any of these non-standard broadcast ...
... recognize and accept any of these non-standard broadcast
addresses as the destination address of an incoming datagram.
...
... host MAY optionally have a configuration option to choose the
0 or the -1 form of broadcast address, for each physical
interface, but this option SHOULD default to the standard (-1)
form.
...
... address instead of a Directed
Broadcast address may improve system robustness. Problems
are often caused by machines that do not understand the
plethora of broadcast ...
... are often caused by machines that do not understand the
plethora of broadcast addresses (see Section 3.2.1.3), or
that may have different ideas about which broadcast
...
... that may have different ideas about which broadcast
addresses are in use. The prime example of the latter is
machines that do not understand subnetting but are
attached to a subnetted net. Sending a Subnet ...
... datagram addressed
to the Limited Broadcast address ought to be sent from all
the interfaces of a multihomed host ...
... networks for which a mapping from Class D IP addresses to
link-layer addresses has been specified (see below). Support
...
... Class D IP addresses to
link-layer addresses has been specified (see below). Support
for local IP multicasting includes sending multicast ...
... The mapping of IP Class D addresses to local addresses is
currently specified for the following types of networks ...
... IP Class D addresses to local addresses is
currently specified for the following types of networks:
...
... 791std5, except for:
SpecDest = specific-destination address of datagram
(defined in Section 3.2.1.3)
...
...
The result parameter dst contains the datagram's destination
address. Since this may be a broadcast or multicast address,
...
... datagram's destination
address. Since this may be a broadcast or multicast address,
the SpecDest parameter (not shown in RFC-791std5) MUST be passed.
...
... addressing (RFC-950std5) |3.2.1.3 |x| | | | |
Src address must be host's own IP address |3.2.1.3 |x| | | | |
...
... Non-initial fragment |3.2.2 | | | | |x|
- Datagram with non-unique src address |3.2.2 | | | | |x|
Return ICMP error msgs (when not prohibited) |3.3.8 |x| | | | |
...
... Discard Echo Request to broadcast address |3.2.2.6 | | |x| | |
Discard Echo Request to multicast address ...
... address |3.2.2.6 | | |x| | |
Discard Echo Request to multicast address |3.2.2.6 | | |x| | |
Use specific-dest addr as Echo Reply src |3.2.2.6 |x| | | | |
...
... | | | | | | |
ICMP Address Mask Request and Reply: | | | | | | |
Addr Mask source configurable |3.2.2.9 |x| | | | |
Support static configuration of addr mask |3.2.2.9 |x| | | | |
...
... no Reply |3.2.2.9 | |x| | | |3
Update address mask from first Reply only |3.2.2.9 |x| | | | |3
Reasonableness check on Addr Mask |3.2.2.9 | |x| | | |
Send unauthorized Addr Mask Reply msgs |3.2.2.9 | | | | |x|
...
... ROUTING OUTBOUND DATAGRAMS: | | | | | | |
Use address mask in local/remote decision |3.3.1.1 |x| | | | |
Operate with no gateways ...
... broadcast |3.3.6 | |x| | | |
Recognize all broadcast address formats |3.3.6 |x| | | | |
Use IP b'cast/m'cast addr in link-layer ...
... When a UDP datagram is received, its specific-destination
address MUST be passed up to the application layer.
...
...
An application program MUST be able to specify the IP source
address to be used for sending a UDP datagram or to leave it
...
... datagram or to leave it
unspecified (in which case the networking software will
choose an appropriate source address). There SHOULD be a
way to communicate the chosen source address up to the
...
... choose an appropriate source address). There SHOULD be a
way to communicate the chosen source address up to the
application layer (e.g, so that the application can later
...
... request/response application that uses UDP should use
a source address for the response that is the same as
the specific destination address of the request. See
...
... a source address for the response that is the same as
the specific destination address of the request. See
the "General Issues" section of [INTRO:1].
...
... Invalid Addresses ...
... A UDP datagram received with an invalid IP source address
(e.g., a broadcast or multicast address ...
... IP source address
(e.g., a broadcast or multicast address) must be discarded
by UDP or by the IP layer ...
... host sends a UDP datagram, the source address MUST be
(one of) the IP address(es) of the host ...
... IP |4.1.3.6 |x| | | | |
Only send valid IP source address |4.1.3.6 |x| | | | |
UDP Application Interface ...
... If an application on a multihomed host does not specify the
local IP address when actively opening a TCP connection,
then the TCP ...
... then the TCP MUST ask the IP layer to select a local IP
address before sending the (first) SYN. See the function
GET_SRCADDR() in Section 3.4.
...
... connection, and TCP MUST use the same
local address is used that was used in those previous
segments.
...
... Remote Address Validation ...
... A TCP implementation MUST reject as an error a local OPEN
call for an invalid remote IP address (e.g., a broadcast or
multicast address ...
...
An incoming SYN with an invalid source address must be
ignored either by TCP or by the IP layer ...
...
OPEN( ... [local IP address,] ... )
...
...
to allow the specification of the local IP address.
...
... Some TCP-based applications need to specify the local
IP address to be used to open a particular connection;
FTP ...
...
A passive OPEN call with a specified "local IP address"
parameter will await an incoming connection request to
...
... parameter will await an incoming connection request to
that address. If the parameter is unspecified, a
passive OPEN will await an incoming connection ...
... passive OPEN will await an incoming connection request
to any local IP address, and then bind the local IP
address of the connection to the particular address ...
... incoming connection request
to any local IP address, and then bind the local IP
address of the connection to the particular address
...
... IP address, and then bind the local IP
address of the connection to the particular address
that is used.
...
...
For an active OPEN call, a specified "local IP address"
parameter will be used for opening the connection. If
...
... connection. If
the parameter is unspecified, the networking software
will choose an appropriate local IP address (see
Section 3.3.4.2) for the connection
...
... port |4.2.2.18|x| | | | |
Ask IP for src address for SYN if necc. |4.2.3.7 |x| | | | |
Otherwise, use local addr of conn. |4.2.3.7 |x| | | | |
...
... OPEN to broadcast/multicast IP Address |4.2.3.14| | | | |x|
Silently discard seg to bcast/mcast addr |4.2.3.14|x| | | | |
...
... Time Exceeded => tell ALP, don't abort |4.2.3.9 | |x| | | |
Param Problem => tell ALP, don't abort |4.2.3.9 | |x| | | |
| | | | | | |
Address Validation | | | | | | |
Reject OPEN call to invalid IP address ...
... IP address |4.2.3.10|x| | | | |
Reject SYN from invalid IP address |4.2.3.10|x| | | | |
Silently discard SYN ...
... 1016, July 1987.
This RFC first described directed broadcast addresses. However, the bulk of the RFC is concerned with gateways, not hosts. ...
This RFC first described directed broadcast addresses. However, the bulk of the RFC is concerned with gateways, not hosts. ...
... Internet architecture generally provides little protection
against spoofing of IP source addresses, so any security mechanism
that is based upon verifying the IP source address ...
... IP source addresses, so any security mechanism
that is based upon verifying the IP source address of a datagram
should be treated with suspicion. However, in restricted
...
... datagram
should be treated with suspicion. However, in restricted
environments some source-address checking may be possible. For
example, there might be a secure LAN whose gateway ...
... host on the LAN could use
the source address to test for local vs. remote source. This problem
is complicated by source routing, and some have suggested that
...
... Author's Address ...