BILLW@MATHOM.CISCO.COM (William Westfield) (11/13/87)
Oops. My question was slightly misunderstood (But it did cause a lot of interesting responses). Perhaps a more detailed explanation is called for, if I can do it without getting overly commercial... There are essentially two models possible for doing a "slip server". At cisco, we refer to these as the "terminal server" model, and the "gateway" model. In the gateway model, each slip connection has its own subnet, possibly with another network on the other end of the link. Information about how to reach hosts on the other side is all exchanged via normal routing protocols, and the box is acting as a real gateway. The host can pick its own IP address by virtue of pretending to be a gateway between the SLIP link (whose address is fixed) and the host's network. In the terminal server model, each slip connection is mapped to a particular IP address, and the box ARPs for all of the resulting IP addresses - essentially acting as a giant, extra long, very slow, multi-port ethernet transceiver. Each slip speaking box gets assigned an IP address on the same subnet as the terminal server itself. Since no routing information is exchanged, only one IP address at the other end is possible, and the slip server gets to pick it. cisco has implemented the terminal server model of a slip server as part of our terminal server. If enabled, users could issue a SLIP command, and the exec prints out info telling them their IP address, and then it goes into a mode where only IP packets are transferred. (How to exchange this sort of information in a machine oriented fashion is an unresolved issue - we're interested in any suggestions). SLIP lines (actually, lines in general) can run up to 38.4Kbps, and of course lines can get configured permanently in SLIP mode too. Up to 96 terminal lines can be put on one box. We think that the gateway model is also implementable, though the idea of an 97 way gateway is somewhat mind-boggling. What may happen in this area is a SLIP driver for the serial (normally HDLC) cards we are currently using. Up to 6 lines per box would be possible. The original question I asked was meant to mean: Given that we have implemented SLIP on our ethernet terminal server, and that we also sell a DDN terminal server (a "TAC" with 1822 or X.25 interfaces), should be also attempt to have the DDN Terminal server ALSO support slip, by way of the logical host mechanism that exists in the DDN network world. Im still interested in the answer to that question, but the discussion on SLIP issues in general is interesting too, though it might be more appropriate for, say, the PCIP mailing list. Bill Westfield cisco Systems. -------
STJOHNS@SRI-NIC.ARPA (11/13/87)
For a terminal server plugged into a class A c30 net, use the 3rd octet of the IP address to differentiate the SLIP ports. I.e. transparent gateways or port expander model. Mike