PMDF System Manager's Guide

The identtcp keyword tells PMDF to perform a connection and lookup using the IDENT protocol (RFC 1413). The information obtained from the IDENT protocol (usually the identity of the user making the SMTP connection) is then inserted into the Received: header for the message, with the hostname corresponding to the incoming IP number, as reported from a DNS reverse lookup, and the IP number itself. The identtcpsymbolic keyword tells PMDF to perform a connection and lookup using the IDENT protocol (RFC 1413). The information obtained from the IDENT protocol (usually the identity of the user making the SMTP connection) is then inserted into the Received: header for the message, with the hostname corresponding to the incoming IP number, as reported from a DNS reverse lookup; the IP number itself is not included in the Received: header. The identtcpnumeric keyword tells PMDF to perform a connection and lookup using the IDENT protocol (RFC 1413). The information obtained from the IDENT protocol (usually the identity of the user making the SMTP connection) is then inserted into the Received: headers of the message, with the actual incoming IP number --- no DNS reverse lookup on the IP number is performed. Note that the remote system must be running an IDENT server in order for the IDENT lookup caused by the identtcp, identtcpsymbolic, or identtcpnumeric to be useful. In addition, be aware that IDENT query attempts may incur a performance hit. Increasingly routers simply "black hole" attempted connections to ports that they don't recognize; if this happens on an IDENT query, then PMDF does not hear back until the connection times out (a TCP/IP package controlled timeout, typically on the order of a minute or two). A lesser performance factor is that when comparing identtcp or identtcpsymbolic vs. identtcpnumeric, note that the DNS reverse lookup called for with identtcp or identtcpsymbolic incurs some additional overhead to obtain the more "user-friendly" hostname.

The identnone keyword disables this IDENT lookup, but does do IP to hostname translation, and both IP number and hostname will be included in the Received: header for the message. The identnonesymbolic keyword disables this IDENT lookup, but does do IP to hostname translation; only the hostname will be included in the Received: header for the message. The identnonenumeric keyword disables this IDENT lookup and inhibits the usual DNS reverse lookup translation of IP number to hostname, and may therefore result in a performance improvement at the cost of less user-friendly information in the Received: headers. identnone is the default.

The identtcplimited and identnonelimited keywords have the same effect as identtcp and identnone, respectively, as far as IDENT lookups, reverse DNS lookups, and information displayed in Received: header lines. Where they differ is that with identtcplimited or identnonelimited the IP literal address is always used as the sole basis for any channel switching due to use of the switchchannel keyword, regardless of whether the DNS reverse lookup succeeds in determining a host name. Note that since channel switching is always performed preferentially based on IP address rather than host name, the effect of identtcplimited or identnonelimited is merely to disable ever trying host name switching in case all IP address rewriting failed.

Keyword	IDENT	DNS	IP address	Reverse hostname	Fall back to
	lookup	reverse	in Received:	in Received:	hostname
		lookup	header line	header line	channel switch
identtcp	Yes	Yes	Yes	Yes	Yes
identtcplimited	Yes	Yes	Yes	Yes	No
identtcpnumeric	Yes	No	Yes	No	No
identtcpsymbolic	Yes	Yes	No	Yes	Yes
identnone	No	Yes	Yes	Yes	Yes
identnonelimited	No	Yes	Yes	Yes	No
identnonenumeric	No	No	Yes	No	No
identnonesymbolic	No	Yes	No	Yes	Yes

The forwardchecknone, forwardchecktag, and forwardcheckdelete channel keywords can modify the effects of doing reverse lookups, controlling whether PMDF does a forward lookup of an IP name found via a DNS reverse lookup, and if such forward lookups are requested what PMDF does in case the forward lookup of the IP name does not match the original IP number of the connection. The forwardchecknone keyword is the default, and means that no forward lookup is done. The forwardchecktag keyword tells PMDF to do a forward lookup after each reverse lookup and to tag the IP name with an asterisk, *, if the number found via the forward lookup does not match that of the original connection. The forwardcheckdelete keyword tells PMDF to do a forward lookup after each reverse lookup and to ignore (delete) the reverse lookup returned name if the forward lookup of that name does not match the original connection IP address, and stick with the original IP address instead. (Note that having the forward lookup not match the original IP address is normal at many sites, where a more "generic" IP name is used for several different IP addresses.)

These keywords are only useful on SMTP channels that run over TCP/IP.