KASTEN@MITVMA.MIT.EDU (Frank Kastenholz) (03/25/88)
A question.... Suppose a host is connected to a network which has two gateways on it (G1 and G2) both of which have valid paths to some destination network (the "cost" of those paths is irrelevant). The host is using G1 to communicate with a host on the destination network and G1 dies with no warning (e.g. the power supply blows up) so that G1 can not send any kind of "I'm Dying" message (This death is NOT an overload due to too many packets that can be fixed with a ICMP Source Quench or Redirect). Are there any rules/guidelines/standards/... as to how the host can "find" G2? Thanks In Advance Frank Kastenholz Atex Inc.
tsuchiya@GATEWAY.MITRE.ORG (Paul Tsuchiya) (03/25/88)
We once did a thing where we picked an Internet Address that all gateways would respond to. When a host did an ARP, several gateways would respond, and the host would pick one of them (I imagine the last, but it rather depends on the host). If the chosen gateway died, then subsequent ARPs would find a living one. In ISO (by the way), we have a host to gateway configuration protocol (called ES-IS) that has a LAN multicast addresses that means "all gateways" or "all hosts". When a hosts hears "all gateways", then he gets the packet, and records the internet level address (Network Entity Title, in ISOese). _________________________________________________________________ Paul F. Tsuchiya The MITRE Corp. tsuchiya@gateway.mitre.org 7525 Colshire Dr. 703-883-7352 McLean, VA 22102 USA _________________________________________________________________
DCP@QUABBIN.SCRC.SYMBOLICS.COM (David C. Plummer) (03/26/88)
Date: Fri, 25 Mar 88 07:52:27 EST
From: tsuchiya@gateway.mitre.org (Paul Tsuchiya)
We once did a thing where we picked an Internet Address that all gateways
would respond to. When a host did an ARP, several gateways would respond,
and the host would pick one of them (I imagine the last, but it rather
depends on the host). If the chosen gateway died, then subsequent ARPs
would find a living one.
Why would you need to ARP again? You already have the protocol address
to hardware address translation, so why do you need to get it again?
Maybe you have a very, VERY small ARP cache timeout?
This doesn't answer the poser's question though, since I think the poser
wanted to know how to rechoose at the IP level, not at the link level.NJG@CornellA (Nick Gimbrone) (03/30/88)
>host is using G1 to communicate with a host on the destination ... >Are there any rules/guidelines/standards/... as to how the host can >"find" G2? We run the IBM product for VM (FAL) and have thought about this same problem. In this case the package is configured with but one "default" gateway. Several alternatives seem to exist (perhaps we'll do one one of these days). One could build a list of "default" gateways and if you note G1 isn't talking start using G2 (G3, G4, etc). You could even add active steps to look for G1 not talking (ping it once in a while?). Another alternative is to "listen" to whatever internal routing protocol is used on the LAN. For us we use lots of RIP, which talks via broadcasts. This makes it easy for any host that cares to to "listen in" on what the RIPers are saying. The host can then act accordingly for all their routing decisions. -njg