SATZ@MATHOM.CISCO.COM (Greg Satz) (10/06/87)
The latest DDN X.25 documentation that I have is dated December 1983. Is there a newer version? I also have a couple of questions regarding the DDN addressing mechanisms when using X.25. 1) Has a DNIC been assigned to the DDN? The DDN X.121 address is comprised of a seven digit address, a flag digit for physical/logical addressing and a sub-address field consisting of two digits. 2) I would appreciate an example of using the physical/logical addressing modes. What are they used for? 3) Since sub-addresses are optional and are only used between consenting DTE implementations, is it safe to ignore them completely? I guess I am asking if anyone knows what these are used for as well. It would be nice if BBN could provide documentation explaining their X.121 addresses a little more clearly. The "how" is explained rather nicely; however, the "what" and "why" were completely overlooked. -------
STJOHNS@SRI-NIC.ARPA (10/06/87)
The 1983 version of the DDN X.25 standard is the most recent. 1)No DNIC has been assigned to any component of the DDN, and at this writing, it doesn't look like one will be assigned. There are only some 20 DNICs allocated to the US. 2) Using the current mappings, the physical mappings are directly translatable into a PSN/Host Port pair. Logical addressing is implemented, but currently not used by anyone since for it to work properly for the IP world, everyone on the subnet has to implement a form of the Logical addressing. Logical Addressing allows several forms of address indirection: a) single host with multiple ports, b) multiple hosts on different ports providing the same service (eg Gateways), c) multiple hosts on the same port, time sharing the port. In each case, the address is resolved at call setup time into a physical address. 3) On the C/30 network, using X.25 standard with IP above it, sub-addresses should NOT be specified and should be ignored if they are. As for the what and why, keep in mind, we have to maintain a valid mappiung from IP to whatever X.25 address we pick. That has a lot to do with "why". Mike