Date: Tue, 6 Apr 1999 11:10:32 -0400 (EDT) From: "Crist J. Clark" <cjc@cc942873-a.ewndsr1.nj.home.com> To: andyo@prime.net.ua (Andy V. Oleynik) Cc: andrea.franceschini@linet.it, freebsd-questions@FreeBSD.ORG Subject: Re: arp. Message-ID: <199904061510.LAA27344@cc942873-a.ewndsr1.nj.home.com> In-Reply-To: <3709F019.6B2D651C@prime.net.ua> from "Andy V. Oleynik" at "Apr 6, 99 02:29:30 pm"
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Andy V. Oleynik wrote,
[Charset koi8-r unsupported, filtering to ASCII...]
> "Crist J. Clark" wrote:
>
> > Andy V. Oleynik wrote,
> > [Charset koi8-r unsupported, filtering to ASCII...]
> > > andrea wrote:
> > >
> > > > I have to add a gateway to my net for experimental reasons.
> > > > Actually there are : a main-router that works as interface to the Internet,
> > > > and some hosts on my sub net.
> > > >
> > > > Internet-----MyRouter----MySubNet
> > > >
> > > > NOw i need to configure one host of MYSubNet to act as a gatway for the
> > > > secondary subnet.
> > > > Both the 1SubNet and 2 SubNEt share the same ip-range.
> > > >
> > > > Internet-----MyRouter----MySubNet-----My2SubNet
> > >
> > > As I understood U have smth like this :
> > > Internet-----MyRouter----MySubNet
> > > |----2ndRouter-----My2SubNet
> >
>
> I mean 2ndrouter is on MySubNet, sorrey for unclearity:)
I meant to say that I assume they are all on the same
LAN. Everything on SubNet1 along with the secondary router are all
"directly" connected to the first router. Representing more of the
hardware involved (if the original poster is out there and still
trying to figure this out, some clarification?),
___
| |---Host1 \
| |---Host2 \___ SubNet1
Internet---PrimaryRouter----|Hub| ... /
| |---HostM /
|___|---SecondaryRouter
|
|
_|_
| |---HostM+1 \
|Hub|---HostM+2 \___ SubNet2
| | ... /
|___|---HostM+N /
> > > Then U have to cut My2SubNet from ur MySubNet and configure
> > > routes to appropriate subnets on appropriate hosts. As long as ur 2ndsubnet
> > > is part of ur mainsubnet the hosts from 2ndsubnet will be seen from internet
> > >
> > > & wise a versa. U may need to run DNS for reverse zone of ur My2SubNet
> >
> > DNS has nothing really to do with this problem. I believe the original
> >
>
> I said "U may" not "U must". At least I run DNS for revzones of my subnets.
But does not have anything to do with this problem.
> > poster is describing the following (this may be what the second poster
> > meant to write, but proportional fonts, tab damage, or his character
> > set wiped it out),
> >
> > Internet------PrimaryRouter------SubNet1
> > |
> > SecondaryRouter-----SubNet2
> >
> > > >
> > > >
> > > > All the sub.net have to be seen from the Internet so I'll need to add a
> > > > route to MainRouter in order to route the Secondary Subnet.
> > > > The problem is that i cannot change configuration of the mainroute,so i
> > > >
> > >
> > > in fact this isnt big problem as soon as U have properly configured
> > > subnets:) . Correct me if I wrong.
> >
> > This is a problem. You are wrong. But back to the original poster, why
>
> Sorrey Crist, but there is no need to connect 2nd router to 1st. If U have to
> have 2nd subnet just insert 2nd NIC into 1st router and as I sad above
> configure ur subnets (with appropriate routes on router off cause &
> defaulterouter on hosts on subnets :).
The first poster claims he cannot reconfigure the router. I think we
can then be fairly confident this means we cannot alter the hardware
in it.
> > can you not change the configuration on the Primary Router[0]? If this is
> > your network, and you want to be able to do things like this, you need
> > to be able to change the Primary Router configuration.
> >
> > To the second poster, when the Primary Router receives a packet
> > destined for a machine on SubNet1 or SubNet2, since the Router
> > believes all of those machines are still on its LAN, it will try to
> > use the MAC address (layer 2) to send the packet directly to the
> >
>
> Is this true if 1strouter knows that a route to 2ndsubnet is throught 2ndrouter
> which is
> on same subnet as 1strouter?
Remeber the original poster did not (or could not) change the
configuration of the primary router. Therefore, the first router has
no idea that it needs to forward packets to the secondary router. It
has no idea there is a second subnet (a sub-subnet if you will).
> > machine. However, now this machine has been moved behind the Secondary
> > Router. The Secondary Router is not listening for other machines'
> >
>
> why not if it's configured as gateway to 2ndsnet?
You do not seem to understand the difference between Layer 2 and Layer
3 of the TCP/IP stack. A router expects packets to be sent directly to
it at Layer 2 (the data link layer) even though these packets are
destined for another machine as indicated in Layer 3 (the network
layer). The second router will send packets out just fine, but since
the primary router does not know that packets need to be sent to the
secondary router to get to the sub-subnet, they never get sent from
primary router to secondary.
A router does not 'listen' for packets to the machines behind it. It
gets packets sent directly to it at layer 2, _only then_ looks at the
IP address on the packet, then decides where it needs to send this
packet (whether another router or directly to the machine in
question).
> > packets at layer 2 (in a typical router setup), so it never gets the
> > packet and never tries to forward it. It also would not respond to ARP
> > calls by the Primary Router when it is looking for a machine on
> > SubNet2.
[remainder snipped]
--
Crist J. Clark cjclark@home.com
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