ginsburg@samsung.COM (Scott Ginsburg) (07/10/90)
I'm trying to get a handle on IP routing and gateway visibility for a device (not necessarily running Unix) on an Ethernet. This device is part of a class C network, has a single Ethernet interface, and there will probably be more than one IP gateway to either the outside world (T1, etc) or another class C network within the same installation on a different Ethernet backbone. My questions are: 1.) Is it the case that I need to provide a default gateway address for IP packets that aren't destined for someone within my subnet? 2.) Do I need to implement an IGP like RIP and maintain routing tables (even though this device only has one network interface) so that I choose the correct gateway to route my outgoing packets to, or is it OK to go to the same gateway (default) every time? 3.) If the answer to 2 is that it's not smart to go to the same gateway every time, then is something like RIP (which should be available on most Unix networks because of routed) the way to go, or does the ICMP redirect take care of letting me know that one internal gateway is better than another for an outgoing packet? Thanks in advance, Scott -- ------------------------------------------------------------------------- Scott Ginsburg WA2CJT Voice: 508-685-7200 FAX: 508-685-4940 Samsung Software America Internet: ginsburg@samsung.com Andover, MA
0004219666@MCIMAIL.COM (Bob Stine) (07/10/90)
> My questions are: > 1.) Is it the case that I need to provide a default gateway > address for IP packets that aren't destined for someone > within my subnet? Only if you want them to get there :-). Seriously, you'll need some sort of route table entry or entries for the networks that you reach by gateway. > 2.) Do I need to implement an IGP like RIP ... > ... (even though this device only has one network > interface) ... I wouldn't. > ... or is it OK to go to the same > gateway (default) every time? Not really, but see below. > 3.) If the answer to 2 is that it's not smart to go to the > same gateway every time, then is something like RIP (which > should be available on most Unix networks because of > routed) the way to go, or does the ICMP redirect take care > of it. Bingo! If you have a decent IP implementation, then it will populate its local routing table when it gets ICMP redirects. BSD 4.3 does this. Probably alot of other IPs do, too. - Bob Stine
booloo@lll-crg.llnl.gov (Mark Boolootian) (07/12/90)
In article <10900710151001.0004219666NB4EM@mcimail.com> 0004219666@MCIMAIL.COM (Bob Stine) writes: > >> 3.) If the answer to 2 is that it's not smart to go to the >> same gateway every time, then is something like RIP (which >> should be available on most Unix networks because of >> routed) the way to go, or does the ICMP redirect take care >> of it. > >Bingo! If you have a decent IP implementation, then it will populate >its local routing table when it gets ICMP redirects. BSD 4.3 does this. >Probably alot of other IPs do, too. > >- Bob Stine The down side to this is that you (potentially) get lots of entries in your routing table. And if you lose the gateway to which you have been redirected, you may not be able to get back to the original gateway (although it is possible that a routing redirect might be removed if the moon is just right...). Just more food for thought. mb food for line eater . . .
jbvb@VAX.FTP.COM (James B. Van Bokkelen) (07/13/90)
The Host Requirements RFC (lower layers, RFC 1122) has quite a bit to say about this: 1.) Is it the case that I need to provide a default gateway address for IP packets that aren't destined for someone within my subnet? Yes. Allowing several would be better than only one. 2.) Do I need to implement an IGP like RIP and maintain routing tables (even though this device only has one network interface) so that I choose the correct gateway to route my outgoing packets to, or is it OK to go to the same gateway (default) every time? It is quite acceptable to go to the first choice until you fail-over to another in the default list based on upper-layer advice or failure to reply to ARP, etc. ICMP Redirect was designed to supplement the default gateway with real-time advice about which gateway of all those Oactive on the net at any given time is "best". The intent was to allow hosts to avoid hacking routing protocols... 3.) If the answer to 2 is that it's not smart to go to the same gateway every time, then is something like RIP (which should be available on most Unix networks because of routed) the way to go, or does the ICMP redirect take care of letting me know that one internal gateway is better than another for an outgoing packet? The problem with implementing one routing protocol is that you'll have to do them all (RIP, IGRP, OSPF, IS-IS....) before you have real interoperability. In particular, there are many people awaiting their chance to be RIP's pallbearers (at least at their local sites). James B. VanBokkelen 26 Princess St., Wakefield, MA 01880 FTP Software Inc. voice: (617) 246-0900 fax: (617) 246-0901