pst@ack.Stanford.EDU (Paul Traina) (02/25/90)
perand@nada.kth.se (Per Andersson) writes: >I'm trying to figure out how to make a ethernet to SLIP gateway out of a >Sparcstation. ... >Oh yes, I must mention that I do not want to allocate a subnet for this single >SLIP-system. And until now I haven't had a reason to run either routed or >gated. 1. there is a file called slipware.tar.Z on neat.cs.toronto.edu which provides slip support for SunOS 4 and its horrible streams. 1a. Van Jacobson's header compression software (including mods) is out in beta test. You may FTP that from rtsg.ee.lbl.gov (the file is called cslipbeta.tar.Z). Now for the fun part. You want to run SLIP to a machine without taking up an entire subnet. I can't think of a reasonable way to do that, _but_ you can still cheat. If you just wanted to hook up one host, you can do it by allocating 4 IP addresses in succession (the first IP address should be on a multiple of 4 boundary). Here is an example that will be real sometime next week. At work, I have ack which is a sparcstation running sunos4. At home, I have another machine called nak. Since I only want to gateway to one host, I allocate a 2-bit subnet (4 network addresses). Example: 36.21.0.158 ack.Stanford.EDU (IP address of gateway enet) 36.21.0.244 ack-nak-network (this is the "0" address) 36.21.0.245 ack-slip (slip port on gateway) 36.21.0.246 nak.Stanford.EDU nak-slip (slip port on home machine) 36.21.0.247 ack-nak-broadcast (this is the "255" address) I then ifconfig ack's slip line with a tiny netmask: ifconfig sl0 ack-slip nak-slip netmask 0xfffffffc Now for the kicker: since we don't run RIP, just proxy-arp for the addresses that the gateway deals with directly: # find out ethernet address -- a kludge but I was being lazy... # etheraddr=`dmesg | grep "Ethernet address" | awk '{ print $4 }'` # # proxy-arp for all addresses we're really taking ourselves. # for host in [ ack-nak-network ack-slip nak-slip ack-nak-broadcast ] do arp -s $host $etheraddr pub done (you may have to use ip addresses if your arp was broken like mine). While this isn't the greatest way of doing things (broadcast traffic could get messy) it works well enough. The general idea is courtesy of Charles Carvalho of ACC in Santa Barbara. Any mistakes made in the presentation are my fault. Cheers and let me know how things work for you, Paul
leres@ace.ee.lbl.gov (Craig Leres) (02/26/90)
Followups to comp.protocols.tcp-ip. Gee, perhaps I'm missing the point but I don't see why you need to use subnets at all. Let's say the slip gateway machine's address is 126.0.128.30 (using a netmask of 0xffffff00). Pick any free address on the subnet for the remote host, say 126.0.128.45. Now on the remote side, ifconfig the slip line (which is a point-to-point) using the ip address we've chosen for the local end (126.0.128.45) and the address of the gateway for the far end (126.0.128.30). Install a static default route via the gateway (126.0.128.30). On the slip gateway, ifconfig the slip line using the gateway and remote addresses (reversed from above). This gives you an interface route to the remote host. Publish an arp entry for the remote host (126.0.128.45) using the ethernet address of the gateway. (Make sure ipforwarding is enabled.) We've been running two slip hosts this way for months now... Craig