Table of Contents for

Squid: The Definitive Guide

Instructs Squid to not store any responses received from the neighbor. This is often useful when you have a cluster and don’t want a resource to be stored on more than one cache.

Allows you to weight parent caches artificially when using ICP/HTCP and all parents report a cache miss. Normally Squid selects the parent whose reply arrived first. In fact, it remembers which parent has the best round-trip time for the query. Squid actually divides the RTT by the weight, so that a parent with weight=2 has lower (better) round-trip times and should be selected more often.

An option for multicast neighbors only. It is the multicast TTL value to use for ICP queries and it controls how far away the ICP queries can travel. The valid range is 0-128. A larger value allows the multicast queries to travel farther and possibly be intercepted by outsiders. Use a lower number to keep the queries close to the source and within your network.

Disables ICP/HTCP for the neighbor. That is, your cache won’t send any queries to the neighbor for cache misses. It is often used with the default option.

Specifies the neighbor as a suitable choice in the absence of other hints. Squid would prefer to forward a cache miss to a parent that is likely to have a cached copy of the particular resource. Sometimes Squid won’t have any clues (e.g., if you disable ICP/HTCP with no-query). In these cases, Squid looks for a parent that has been marked as a default choice.

A simple load-sharing technique. It only makes sense when you mark two or more parent caches as round-robin. Squid keeps a counter for each parent. When it needs to forward a cache miss, Squid selects the parent with the lowest counter.

Tells Squid to expect ICP replies from the neighbor in response to multicast queries.

Refers to Squid’s netdb features. When your neighbor has enabled the network database, it may return ICMP RTT measurements in ICP miss replies. This option instructs Squid to select a parent based on the RTT between the parent and the origin server, rather than the RTT between your cache and the parent.

Tells Squid not to request a Cache Digest from the neighbor. See Section 10.7.

Tells Squid not to request the neighbor’s netdb database. Note, this refers to the bulk transfer of the RTT measurements, not the inclusion of these measurements in ICP miss replies.

Tells Squid to ignore any delay pools settings for requests to the neighbor. See Appendix C.

Instructs Squid to send authentication credentials to the neighbor. This option has three different formats, which I’ve fully described in Section 10.3.1.

Specifies how long Squid should wait when establishing a TCP connection to the neighbor. Without this option, the timeout is taken from the global connect_timeout directive. By using a lower timeout, Squid gives up on the neighbor quickly and tries forwarding the request elsewhere.

Specifies the URL for the neighbor’s Cache Digest. Without this option, Squid assumes the digest URL is http://neighbor.host.name:port/squid-internal-periodic/store_digest.

Instructs Squid to omit the Cache-control: only-if-cached directive for requests sent to a sibling. You should use this only if the neighbor is using the icp_hit_stale and isn’t using a miss_access list.

Places a limit on the number of simultaneous connections that Squid can open to the neighbor. When this limit is reached, Squid excludes the neighbor from its selection algorithm.

Tells Squid to send HTCP, instead of ICP, queries to this neighbor. If you add this option, don’t forget to also change the port number. Squid uses 4827 as the default HTCP port. See Chapter 10.

Tells Squid that this neighbor is a member of a CARP array. The load factor value specifies the fraction of requests that this neighbor will receive. The load factor values for all neighbors must add up to 1.0. See Chapter 10.