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Chapter 3
Web Proxy Caching
Traffic Server provides many configurable options for supporting parent NNTP servers. The following
sections describe Traffic Server’s NNTP features.
Traffic Server as a news server
When clients want to read news, they access a news server. The news server offers a list of groups to which
clients can subscribe. For each subscribed group, the clients read an overview list of the articles in the group,
and then select an article to read. When Traffic Server acts as a news server, it:
•
Maintains lists of supported news groups
•
Accepts news feeds for each supported news group
•
Serves requested articles to users
•
Accepts and numbers user postings to its supported news groups
Traffic Server as a caching proxy news server
When Traffic Server acts as a caching proxy news server for a particular news server, it:
•
Maintains lists of the news groups on its parent NNTP servers. You can configure the frequency that
Traffic Server updates its copies of group lists.
•
Caches and serves article overview lists on demand. You can also tell Traffic Server to pull article
overview lists from the parent news server periodically.
•
Caches and serves articles on demand. Traffic Server can also accept news feeds, like any news server.
•
Caches and serves miscellaneous LIST files, such as subscription files.
•
Sends user postings to the parent news server.
When clients issue news requests, Traffic Server intercepts these requests and serves them from its cache,
reducing traffic to parent news servers. If a particular overview or article is not in the cache, Traffic Server
forwards requests to the parent server.
Supporting several parent news servers
Traffic Server can cache articles for several news servers. You specify all of the parent news servers for Traffic
Server in the
nntp_servers.config
file. See
nntp_servers.config‚ on page 177
. For each parent news
server, you can have Traffic Server cache some or all of that server’s news groups.
Some of the possible parent configurations that Traffic Server supports are as follows:
Several news servers supplying the same groups
Several news servers can be configured to redundantly serve the same groups, providing enhanced reliability.
Traffic Server provides the following features for managing these configurations:
•
Priorities
If Traffic Server has to contact a parent news server for information about a group supplied by several news
servers, Traffic Server contacts the news server with the highest priority.
•
Round-robin
If several parent news servers supplying the same group have the same priority, Traffic Server selects a
parent news server in round-robin fashion.
•
Failover
If a request to a parent server fails, Traffic Server tries the next server in the round-robin (of the same
priority), and then servers of lower priority.