ARP
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... LINK:1], and trailer negotiation
is performed at the time that ARP is used to discover the
link-layer address of a destination ...
...
Specifically, the ARP exchange is completed in the usual
manner using the normal IP protocol type, but a host ...
... host that
wants to speak trailers will send an additional "trailer
ARP reply" packet, i.e., an ARP reply that specifies the
trailer encapsulation ...
... wants to speak trailers will send an additional "trailer
ARP reply" packet, i.e., an ARP reply that specifies the
trailer encapsulation protocol type but otherwise has the
...
... trailer encapsulation protocol type but otherwise has the
format of a normal ARP reply. If a host configured to use
trailers receives a trailer ARP ...
... ARP reply. If a host configured to use
trailers receives a trailer ARP reply message from a
remote machine, it can add that machine to the list of
...
... remote machine, it can add that machine to the list of
machines that understand trailers, e.g., by marking the
corresponding entry in the ARP cache.
...
... Hosts wishing to receive trailer encapsulations send
trailer ARP replies whenever they complete exchanges of
normal ARP messages for IP ...
... trailer ARP replies whenever they complete exchanges of
normal ARP messages for IP. Thus, a host that received an
...
... a host that sent the IP ARP request would send a trailer
ARP reply when it received the corresponding IP ...
... IP ARP request would send a trailer
ARP reply when it received the corresponding IP ARP reply.
...
... ARP reply when it received the corresponding IP ARP reply.
In this way, either the requesting or responding host in
...
...
This scheme, using extra trailer ARP reply packets rather
than sending an ARP request for the trailer protocol type,
...
... This scheme, using extra trailer ARP reply packets rather
than sending an ARP request for the trailer protocol type,
was designed to avoid a continuous exchange of ARP packets
...
... than sending an ARP request for the trailer protocol type,
was designed to avoid a continuous exchange of ARP packets
with a misbehaving host that, contrary to any
...
... with a misbehaving host that, contrary to any
specification or common sense, responded to an ARP reply
for trailers with another ARP reply for IP ...
... specification or common sense, responded to an ARP reply
for trailers with another ARP reply for IP. This problem
is avoided by sending a trailer ARP ...
... ARP reply for IP. This problem
is avoided by sending a trailer ARP reply in response to
an IP ARP ...
... IP ARP reply only when the IP ARP reply answers an
outstanding request; this is true when the hardware
address for the host ...
... hardware
address for the host is still unknown when the IP ARP
reply is received. A trailer ARP reply may always be sent
...
... Address Resolution Protocol -- ARP ...
... ARP Cache Validation ...
...
An implementation of the Address Resolution Protocol (ARP)
[LINK:2] MUST provide a mechanism to flush out-of-date cache ...
... 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 ...
...
The ARP specification [LINK:2] suggests but does not
require a timeout mechanism to invalidate cache ...
... addresses. The
prevalence of proxy ARP (see Section 2.4 of [INTRO:2])
has significantly increased the likelihood that cache ...
... entries in hosts will become invalid, and therefore
some ARP-cache invalidation mechanism is now required
for hosts ...
... for hosts. Even in the absence of proxy ARP, a long-
period cache timeout is useful in order to
...
... period cache timeout is useful in order to
automatically correct any bad ARP data that might have
been cached.
...
... "refreshed" (by observing the source fields,
regardless of target address, of an ARP broadcast
from the system in question). For proxy ...
... broadcast
from the system in question). For proxy ARP
situations, the timeout needs to be on the order
of a minute.
...
... remote host by
periodically sending a point-to-point ARP Request
to it, and delete the entry if no ARP ...
... ARP Request
to it, and delete the entry if no ARP Reply is
received from N successive polls. Again, the
timeout should be on the order of a minute, and
...
... call the link-layer advice routine to invalidate
the ARP cache entry.
...
...
Approaches (1) and (2) involve ARP cache timeouts on
the order of a minute or less. In the absence of proxy
...
... the order of a minute or less. In the absence of proxy
ARP, a timeout this short could create noticeable
overhead ...
... ARP Packet Queue ...
... Destination Unreachable error to
IP solely because there is no ARP cache entry for a destination.
...
... |2.3.1 | | |x| | |
Send Trailers by default without negotiation |2.3.1 | | | | |x|
ARP |2.3.2 | | | | | |
Flush out-of-date ARP cache entries |2.3.2.1|x| | | | |
...
... |2.3.1 | | | | |x|
ARP |2.3.2 | | | | | |
Flush out-of-date ARP cache entries |2.3.2.1|x| | | | |
Prevent ARP floods |2.3.2.1|x| | | | |
...
... Flush out-of-date ARP cache entries |2.3.2.1|x| | | | |
Prevent ARP floods |2.3.2.1|x| | | | |
Cache timeout configurable |2.3.2.1| |x| | | |
...
... Send K1=6 encapsulation |2.3.3 | | | | |x|
Use ARP on Ethernet and IEEE 802 nets |2.3.3 |x| | | | |
...
... TOS to link layer |2.4 |x| | | | |
No ARP cache entry treated as Dest. Unreach. |2.4 | | | | |x|
...
... Failure to ARP or to re-validate ARP mappings may
be used as negative advice for the corresponding
IP address ...
... the cache entries themselves, a two level data
structure (perhaps coordinated with ARP or similar
caches) may be desirable for implementing a route
cache ...