Date: Thu, 7 May 1998 20:23:24 -1000 From: "Randal S. Masutani" <randal@comtest.com> To: freebsd-net@FreeBSD.ORG Cc: Richard Wackerbarth <rkw@dataplex.net> Subject: Re: Have I left something out? Message-ID: <199805080606.UAA04245@oldyeller.comtest.com> In-Reply-To: <l03130300b17815ebf637@[208.2.87.10]> References: <199805071926.JAA03049@oldyeller.comtest.com>
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On 7 May 98 at 21:02, Richard Wackerbarth wrote: > At 2:42 PM -0500 5/7/98, Randal S. Masutani wrote: > >> Consider the simple case of a loop. For discussion, we will have 6 nets. > >> 10.0.1.0/24, 10.0.2.0/24, ..., 10.0.6.0/24. > >> We will join them with routers > >> 10.0.1.1 == 10.0.2.1 > >> 10.0.2.2 == 10.0.3.2 > >> ... > >> 10.0.5.5 == 10.0.6.5 > >> and to close the loop > >> 10.0.6.6 == 10.0.1.6 > > >> It never finds the "backdoor", 10.0.6.6. > > >Well is supposed to work that way. If you down the interface 10.0.1.6 then by > >definition that host is down. Host 10.0.1.1 cannot get to 10.0.1.6 by > >any other route, other than by its own interface 10.0.1.1 for network 10.0.1.0. > >What you are asking is that Host 10.0.1.1 redirect its interface for net > >10.0.1.0 to route thru 10.0.2.1. This is not possible. As far as Host > >10.0.1.1 is concerned it sees Host 10.0.1.6 as down. However, Host 10.0.1.1 can > >access the Host 10.0.6.1 indirectly as Host 10.0.6.6. > > I disagree. If that were the case, NO machine should be able to find it. > However, machine 5 thinks that it is one hop away; > Machine 4 thinks that it is 2 hops away; > Machine 3 finds that it is 3 hops away; > etc. > > Only the last machine fails to realize that there is another way to get there. That is true. All other machines can still route to it because they are not directly connected. What I said above only applies to that last machine, because it is directly connected to the 10.0.1.0 net. The Host 10.0.1.1 is setup to access subnet 10.0.1.0 only thru its directly connect interface. Since your subnet MASK is set to 255.255.255.0 it will try to access any host number from 10.0.1.2 to 10.0.1.254 thru that interface 10.0.1.1. So you cannot reroute 10.0.1.6 to another route because it falls within you subnet mask and according to routing rules it will only route it to the directly connected network 10.0.1.0. Only if the host fall outside of the subnet mask range then you will be able to reroute the address thru another interface. > >However, Host 10.0.1.1 can access the Host 10.0.6.1 indirectly as Host 10.0.6.6. > > Well, there is a logical inconsistency here. Am I addressing the host or > the interface? both, the host address is bound to the interface. you cannot separate the two. sorry, i made a typo above(10.0.6.1 is meant to be 10.0.1.6.) Let me explain it again. Since the host 10.0.1.6 has a second interface as 10.0.6.6, others computers can still access host 10.0.1.6 thru the 10.0.6.6 interface. But any computer that is on the 10.0.1.0 net cannot access host 10.0.1.6 because they are directly connected. And as I explained above their subnet mask will require them to ARP for the address 10.0.1.6, because it is directly connected. However, the hosts on net 10.0.1.0 can still access that compter(10.0.1.6) as host 10.0.6.6. > Anyone who cannot directly access the interface ends up getting the host. > When it is up, anyone addressing the interface, also gets the host. > > If a host has multiple interfaces, how do I address a SERVICE on that host is > such a way that I get access whenever possible? If I ask DNS for an address, > I get the address of an interface (which may be down). > > Richard Wackerbarth DNS as it currently is, is setup thru static files. What you are asking for is Dynamic DNS lookups. So if one of your interfaces goes down then a dynamic DNS server could change the entry to the active address(which is on the other interface.) I know that there is talk about Dynamic DNS, but I do not know when or how it will be implemented. Randal Masutani ------------------------------------------------------------------------- ComTest Technologies, Inc. 3049 Ualena St., Suite 1005 Honolulu, Hawaii 96819 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-net" in the body of the message
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