Restricting NNTP Access

Access to NNTP resources is governed by the file nntp_access in /usr/lib/news. Lines in the file describe the access rights granted to foreign hosts. Each line has the following format:

           site   read|xfer|both|no    post|no      [!exceptgroups]

If a client connects to the NNTP port, nntpd attempts to obtain the host's fully qualified domain name from its IP-address by reverse lookup. The client's hostname and IP-address are checked against the site field of each entry in the order in which they appear in the file. Matches may be either partial or exact. If an entry matches exactly, it applies; if the match is partial, it only applies if there is no other match following which is at least as good. site may be specified in one of the following ways:

hostname

This is a fully qualified domain name of a host. If this matches the client's canonical hostname literally, the entry applies, and all following entries are ignored.

IP address

This is an IP address in dotted quad notation. If the client's IP address matches this, the entry applies, and all following entries are ignored.

domain

name This is a domain name, specified as *.domain. If the client's hostname matches the domain name, the entry matches.

network name

This is the name of a network as specified in /etc/networks. If the network number of the client's IP address matches the network number associated with the network name, the entry matches.

default

The default matches any client.

Entries with a more general site specification should be specified earlier, because any matches by these will be overridden by later, more exact matches.

The second and third field describe the access rights granted to the client. The second details the permissions to retrieve news by pulling (read), and transmit news by pushing (xfer). A value of both enables both, no denies access altogether. The third field grants the client the right to post articles, that is, deliver articles with incomplete header information which is completed by the news software. If the second field contains no, the third field is ignored.

The fourth field is optional, and contains a comma-separated list of groups the client is denied access to.

A sample nntp_access file is shown below:

           #
           # by default, anyone may transfer news, but not read or post
           default                 xfer            no
           #
           # public.vbrew.com offers public access via modem, we allow
           # them to read and post to any but the local.* groups
           public.vbrew.com        read            post    !local
           #
           # all other hosts at the brewery may read and post
           *.vbrew.com             read            post