RE: IP_alias under Red Hat

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

Hi Brain,
I'm going to do some tests according with what you said. I will inform every
body.

Thank a lot
Moussa BAGAYOKO

> -----Message d'origine-----
> De : owner-afnog at afnog.org [mailto:owner-afnog at afnog.org]De la part de
> Brian Candler
> Envoye : dimanche 19 janvier 2003 19:40
> A : Moussa Bagayoko
> Cc : Mark Tinka; afnog at afnog.org
> Objet : Re: IP_alias under Red Hat
>
>
> On Thu, Jan 16, 2003 at 04:54:09PM -0000, Moussa Bagayoko wrote:
> > 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 first IP address you gave makes no sense - it has 5 dotted parts!
> I will guess you meant: 216.252.180.3. If that is right, then:
>
> > 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).
>
> Are you saying that the router also has two IP addresses,
> 216.252.179.1 and
> 216.252.180.1 (both /25) ? If it's a Cisco, that would be
>
>     int ethernet x
>       ip address 216.252.179.1 255.255.255.128
>       ip address 216.252.180.1 255.255.255.128 secondary
>
> If that's true, then what we have so far is:
>
>                              216.252.179.10    216.252.179.1 (/25)
>        ?              ?      216.252.180.3     216.252.180.1 (/25)
> client ----------------dialup-------------------------------R-----
>            ppp         server            ethernet
>
>
> > When client arrive with IP in the same bloc of eth0 e.g
> 216.252.180.11 there
> > is no problem; all is right.
>
> Is the dial-up server using proxy-arp, to make those ethernet IPs
> available
> to the clients?
>
> > 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.
>
> If you are using proxy-arp (and there's now a long chain of
> "ifs..." in the
> above :-) then it might be that Linux doesn't proxy-arp for alias
> addresses.
>
> One suggestion would be to get rid of the proxy-arp, at least for one of
> your networks (say 216.252.179.0/25). This then becomes a
> dedicated "dial-up
> pool".
>
> You could do so like this:
>
> (1) Remove the 216.252.179 addresses from both the dial-up server and the
> router completely
>
> (2) Add a static route on R:
>
>       ip route 216.252.179.0 255.255.255.128 216.252.180.3
>
> Then you have:
>
>        ?              ?      216.252.180.3     216.252.180.1
> client ----------------dialup-------------------------------R-----
>            ppp         server            ethernet
>
>   ^
>   +--- addresses from
>        216.252.179.0/25 pool
>
> Whenever a client is given an address from the 216.252.179.x
> range, there is
> no need for it to be an alias on the ethernet at all. Router R knows to
> forward any packet with that destination address to the dial-up
> server; the
> dial-up server knows to forward it to the client (it will have a separate
> /32 route in its forwarding table for each host)
>
> The above approach assumes you have a single dialup server. If
> you have more
> than one dialup server, you would give each one its own pool, with its own
> route on R pointing at the right dialup server.
>
> It doesn't work if you have multiple dialup servers but your clients get
> "static IP addresses". But then, nor does proxy-arp (because if you client
> dials server A, then redials and gets server B, they will lose
> connectivity
> until the ARP cache on router R expires)
>
> B.
>
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