IPv6 in C-Kermit

C-Kermit introduced IPv6 support in version 11.0.

This support includes full IPv6 support for Kermit’s own sockets (raw, telnet, and SSL/TLS) as well as the FTP and HTTP clients. The FTP client adds support for EPRT and EPSV as necessary for IPv6.

Notes on usage

SET TCP ADDRESS-FAMILY lets you configure whether to use IPv4, IPv6, or both (the default).

When giving a string that contains an IP address and a port number separated by colons, an IPv6 address (which itself contains colons) must be enclosed in [ and ] brackets. This mimics behavior in other situations (such as URLs) where similar situations are encountered. When a port number is not expected, neither are brackets.

A new option SET TCP ADDRESS6 exists as an analog to SET TCP ADDRESS, letting you specify a local binding address for IPv6.

Areas where IPv6 is unsupported

Where additional libraries must be called differently for IPv6, these occur in rarely-used corners of C-Kermit. Supporting the many possible combinations of system and library IPv6 support is complex. Therefore, these areas of the code remain IPv4-only:

• Kerberos 4 (the wire protocol is incompatible with IPv6, so it will never suport IPv6)

• Some aspects of Kerberos 5 (such as SET AUTHENTICATION KERBEROS5 ADDRESSES)

• GSSAPI; IPv6 support requires different GSSAPI calls

• X11 forwarding will work across an IPv6 connection, but will always listen on an IPv4 socket locally.

• The SSL code doesn’t yet support IPv6 literals in the SAN field. SSL in general is IPv6-capable; this is an exceptionally rare edge case that adds complexity to the code that seemed not worth it in the end.

• rlogin has not been rigorously defined for IPv6 contexts and rlogin behavior is untested there, though may work.