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... ICP is a message format used for communicating between Web caches.
Although Web caches use HTTP ...
... message format used for communicating between Web caches.
Although Web caches use HTTP[1] for the transfer of object data,
...
... HTTP[1] for the transfer of object data,
caches benefit from a simpler, lighter communication protocol. ICP
is primarily used in a cache ...
... caches benefit from a simpler, lighter communication protocol. ICP
is primarily used in a cache mesh to locate specific Web objects in
neighboring caches. One cache ...
... is primarily used in a cache mesh to locate specific Web objects in
neighboring caches. One cache sends an ICP query ...
... cache mesh to locate specific Web objects in
neighboring caches. One cache sends an ICP query to its neighbors ...
... query/reply exchange needs to occur quickly, typically within a
second or two. A cache cannot wait longer than that before beginning
to retrieve an object. Failure to receive a reply message most
...
... neighbor. As an
indication of immediate network conditions between neighbor caches,
ICP over a lightweight protocol such as UDP ...
... In addition to its use as an object location protocol, ICP messages
can be used for cache selection. Failure to receive a reply from a
cache may indicate a network ...
... can be used for cache selection. Failure to receive a reply from a
cache may indicate a network or system failure. The ICP ...
... ICP_OP_INVALID
A place holder to detect zero-filled or malformed messages. A
cache must never intentionally send an ICP_OP_INVALID message.
ICP ...
... Host Address is not that of the
cache generating the ICP message, but rather the address of the
...
... ICP message, but rather the address of the
caches's client that originated the request. The Requester Host
...
... QUERY, but for use in simulating a query to a
cache which does not use ICP. When ICP is used to choose the
...
... HIT response indicates that the requested URL exists in
this cache and that the requester is allowed to retrieve it.
ICP ...
... ICP_OP_MISS response indicates that the requested URL does not
exist in this cache. The querying cache may still choose to fetch
the URL ...
... URL does not
exist in this cache. The querying cache may still choose to fetch
the URL from the replying cache ...
... ICP_OP_MISS_NOFETCH
An ICP_OP_MISS_NOFETCH response indicates that this cache is up,
but is in a state where it does not want to handle cache ...
... cache is up,
but is in a state where it does not want to handle cache misses.
An example of such a state is during a startup phase where a cache ...
... cache misses.
An example of such a state is during a startup phase where a cache
might be rebuilding its object store. A cache in such a mode may
...
... state is during a startup phase where a cache
might be rebuilding its object store. A cache in such a mode may
wish to return ICP_OP_HIT ...
... ICP_OP_MISS reply is an invitation to fetch the
URL from the replying cache (if their relationship allows it), but
ICP_OP_MISS_NOFETCH is a request to NOT fetch the URL ...
... An ICP_OP_DENIED response indicates that the querying site is not
allowed to retrieve the named object from this cache. Caches and
proxies ...
... ICP_OP_DENIED response indicates that the querying site is not
allowed to retrieve the named object from this cache. Caches and
proxies may implement complex access controls. This reply must be
...
... URL from me at this particular time."
Caches receiving a high percentage of ICP_OP_DENIED replies are
...
... receiving a high percentage of ICP_OP_DENIED replies are
probably misconfigured. Caches should track percentage of all
replies which are ICP_OP_DENIED and disable a neighbor ...
... queries).
Similarly, a cache should track the percent of ICP_OP_DENIED
messages that are sent to a given address ...
... denied messages exceeds a certain threshold (e.g. 95% of 100 or
more), the cache may choose to ignore all subsequent ICP_OP_QUERY
...
... Wessels D., Claffy K., "ICP and the Squid Web Cache", National Laboratory for Applied Network Research, http://www.nlanr.net/~wessels/Papers/icp-squid.ps.gz ...
... Wessels D., "The Squid Internet Object Cache", National Laboratory for Applied Network Research, http://squid.nlanr.net/Squid/ ...