RE: IP_alias under Red Hat

["Moussa Bagayoko" <moussa at afribone.net.ml>]

Hi Brian
You didn't understand very much. let me explain the problem with schemes. I
have the following situations
		ppp link			ethernet link
client------------------dial up-----------------------router------>internet
				server				  R

The dial up server has two IP address
eth0 216.252.179.180.3 mask 255.255.255.128
eth0:0 216.252.179.10 mask 255.255.255.128

The default gw on the dial up server is 216.252.180.1 (the router R that has
216.252.179.1 as IP_alias).

When client arrive with IP in the same bloc of eth0 e.g 216.252.180.11 there
is no problem; all is right.
So in the case where client has ip in the same bloc of eth0:0 e.g.
216.252.179.123  he cannot do anything outiside the dialserver. That's a
problem.

I don't no whether the problem come from the dial up server or the router R
even it has ip address in both ip bloc.

Thanks for your help
Moussa BAGAYOKO

> -----Message d'origine-----
> De : owner-afnog at afnog.org [mailto:owner-afnog at afnog.org]De la part de
> Brian Candler
> Envoye : mercredi 15 janvier 2003 15:26
> A : Moussa Bagayoko
> Cc : Mark Tinka; afnog at afnog.org
> Objet : Re: IP_alias under Red Hat
>
>
> On Wed, Jan 15, 2003 at 12:56:48PM -0000, Moussa Bagayoko wrote:
> > Thank for your quick response. I tried with eth0:0 and eth0:eth0.
> > Actually the alias is ok with . All two address is reachable trough
> > internet. So I'm using this machine as modem server and some client get
> > connected with ip adress in the server ip alias bloc and they
> can do nothing
> > outside the server. But they can ping all two server ip
> address. If they get
> > connected with ip in the server primary ip bloc, all is right.
>
> I'm not sure exactly what you mean here.
>
> You can't give the same IP address to both the dial-in server and the
> client:
>
>                                          10.0.0.1 and
>                     modem link           10.0.0.2
>         client - - - - - - - - - dial-up -----------------R---> Internet
>         10.0.0.2                 server
>
> This simply won't work. When an inbound packet arrives from the
> Internet to
> 10.0.0.2, it will be delivered to the dial-up server (which says "10.0.0.2
> is one of my own IP addresses, this packet is for me") and it won't be
> forwarded down the modem link.
>
> So the next thing you might try is to remove 10.0.0.2 as an alias:
>
>                     modem link           10.0.0.1
>         client - - - - - - - - - dial-up -----------------R---> Internet
>         10.0.0.2                 server
>
> The problem here is that when a machine on the Internet tries to send a
> packet to 10.0.0.2, it will get as far as the router R. R will try to send
> an ARP packet for 10.0.0.2, but nobody will respond. So the
> packet won't be
> delivered.
>
> You have two solutions:
>
> (1) Put a static route on router R,
>
>           ip route 10.0.0.2 255.255.255.255 10.0.0.1
>
>     (note: if your dial-up server has more than one phone line then you
>      should allocate a block of IPs, which is in a different subnet, and
>      use that as your dialup pool)
>
> (2) Enable 'proxy-ARP' on the dial-up server for 10.0.0.2. Then, when
>     router R ARPs for 10.0.0.2, the dial-up server will respond saying
>     "yes that's me". R will send the packet over the ethernet to that
>     MAC address. When R receives the packet, it will forward it using its
>     own forwarding table.
>
> With Linux pppd, you could configure than easily: something like this
>
> [/etc/ppp/options.ttyS0]
>    :10.0.0.2 proxyarp
>
> With multiple phone-lines you write a separate options file with
> a different
> IP address for each line.
>
> If I have misunderstood your problem - then a diagram like one of
> the above
> would be very helpful in trying to understand what you're doing.
>
> Regards,
>
> Brian.
>
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