DHCP
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... address using the INIT-REBOOT mechanism, the DHCP specification does
not require the client to perform address conflict detection ...
... client to perform address conflict detection, so this
seven-second delay does not apply. However, the DHCP server may be
slow to respond or may be down and not responding at all, so hosts
...
... The alternative mechanism specified by this document applies when a
host has a previously allocated DHCP address, which was not returned
to the DHCP server ...
... DHCP address, which was not returned
to the DHCP server via a DHCPRELEASE message, and which still has
time remaining on its lease. In this case, the host may determine
...
... performance optimization. Its purpose is to speed
up a process that may require as much as a few hundred
milliseconds (DHCP INIT-REBOOT), as well as to reduce multi-
second conflict detection delays when a host ...
... DNAv4 fails to provide a
benefit, it should add little or no delay compared to today's
DHCP processing. In practice, this implies that DHCP
processing needs to proceed in parallel. Waiting for DNAv4 ...
... benefit, it should add little or no delay compared to today's
DHCP processing. In practice, this implies that DHCP
processing needs to proceed in parallel. Waiting for DNAv4 to
...
... processing needs to proceed in parallel. Waiting for DNAv4 to
fail before beginning DHCP processing can greatly increase
total processing time, the opposite of the desired effect.
...
... Internet host using the Dynamic
Host Configuration Protocol (DHCP) [RFC2131] to obtain
configuration parameters ...
... address assigned via DHCPv4 that
has not been returned to the DHCP server via a DHCP RELEASE
message, and whose lease has not yet expired.
...
... DHCPv4 that
has not been returned to the DHCP server via a DHCP RELEASE
message, and whose lease has not yet expired.
...
...
[2] The IPv4 configuration parameters, including the DHCP client
identifier, assigned address, and lease expiration time.
...
... when the host has previously completed conflict detection as
recommended in Section 2.2 of the DHCP specification [RFC2131] and
obtained an operable IPv4 configuration ...
... conflict is when:
o a DHCP server hands out an address lease,
...
... DHCP server is power-cycled or crashes and is rebooted,
o the DHCP server, having failed to save leases to stable
storage, assigns that same address to another host ...
... address.
While Section 4 of the DHCP specification [RFC2131] assumes that DHCP
servers save their leases in persistent storage, almost no consumer-
...
... While Section 4 of the DHCP specification [RFC2131] assumes that DHCP
servers save their leases in persistent storage, almost no consumer-
grade NAT gateway ...
... grade NAT gateway does so. Short DHCP lease lifetimes can mitigate
this risk, though this also limits the operable candidate
...
... ARP, which is insecure. Hosts that have been
configured to attempt DHCP authentication SHOULD NOT utilize the
reachability test. Security issues ...
... Security issues are discussed in Section 4.
[d] The contents of the DHCP Client Identifier option that the client
used to obtain the candidate ...
... used to obtain the candidate configuration is different from the
DHCP Client Identifier option the client intends to present on
the interface ...
... the interface in question. In this case, it is anticipated that
a DHCP server would NAK any request made by the client to acquire
...
... INIT-REBOOT state, as described in Section 3.2
and 4.3.2 of the DHCP specification [RFC2131], completes more quickly
than the reachability ...
...
In situations where both DNAv4 and DHCP are used on the same link, it
is possible that the reachability ...
... is possible that the reachability test will complete successfully,
and then DHCP will complete later with a different result. If this
happens, the implementation SHOULD abandon the reachability test
...
... reachability test
results and use the DHCP result instead, unless the address confirmed
via the reachability ...
...
Where DNAv4 and DHCP are tried in parallel, one strategy is to
forsake reachability test retransmissions ...
... forsake reachability test retransmissions and to allow only the DHCP
client to retransmit. In order to reduce competition between DNAv4
and DHCP ...
... DHCP
client to retransmit. In order to reduce competition between DNAv4
and DHCP retransmissions, a DNAv4 implementation that retransmits may
...
... utilize the retransmission strategy described in Section 4.1 of the
DHCP specification [RFC2131], scheduling DNAv4 retransmissions ...
...
If a response is received to any reachability test or DHCP message,
pending retransmissions are canceled. It is RECOMMENDED that a DNAv4 ...
... subject to the lease re-
acquisition and expiration behavior described in Section 4.4.5 of the
DHCP specification [RFC2131].
...
... broadcast address, as described in Section 4.4.1 of the
DHCP specification [RFC2131]. If the host supports the Rapid Commit
...
... DHCPDISCOVER, then it retransmits as specified in Section 4.1 of the
DHCP specification [RFC2131].
...
... INIT or REBOOTING state that knows the address of a DHCP
server may use that address in the DHCPDISCOVER or DHCPREQUEST ...
... INIT-REBOOT state is
not appropriate, since if the DHCP client has moved to another
subnet, a DHCP server response ...
... DHCP client has moved to another
subnet, a DHCP server response cannot be routed back to the client
since the DHCPREQUEST ...
... since the DHCPREQUEST will bypass the DHCP relay and will contain an
invalid source address.
...
... address may be legitimately regarded as being reserved for exclusive
use by the assigned host. DHCP-assigned addresses fit this
description, but IPv4 Link-Local ...
... state and sending a DHCPDISCOVER packet, as
described in Section 2.3 of the DHCP specification [RFC2131]. Where
a host ...
... DHCPv4 client does not receive a response after employing the
retransmission algorithm, Section 3.2 of the DHCP specification
[RFC2131] states that the client ...
... DNAv4, manually assigned addresses may be treated
as equivalent to DHCP-assigned addresses with an infinite lifetime.
...
... conflict as long as the manually assigned address is reserved by the
DHCP server or is outside the scope of addresses assigned by a DHCP
server. However, where the manually assigned address ...
... DHCP server or is outside the scope of addresses assigned by a DHCP
server. However, where the manually assigned address is within an
address scope ...
... address is within an
address scope utilized by a DHCP server, it is possible that the host
will be unavailable ...
... host
will be unavailable when the DHCP server checks for a conflict prior
to assigning the conflicting address. In this case, a host ...
... address was not suitable for some reason.
Therefore, where DNAv4 and DHCP are run in parallel and DNAv4
confirms a manual configuration ...
... confirms a manual configuration, it may be undesirable to allow this
configuration to be overridden by DHCP, as described in Section 2.1.
However, packet loss may cause the reachability ...
... packet loss may cause the reachability test to fail while
DHCP completes successfully, resulting in the host obtaining a
dynamic address ...
... aggressive retransmission strategy than that detailed in Section 4.1
of the DHCP specification [RFC2131]. For example, shorter
retransmission ...
... DNAv4) is based on ARP and
DHCP and inherits the security vulnerabilities of these two
protocols.
...
... IP configuration SHOULD NOT use DNAv4 but
SHOULD instead utilize DHCP authentication [RFC3118], possibly in
combination with the Rapid Commit Option [RFC4039 ...