On Wed, 2007-01-31 at 13:12 -0800, Tom Eastep wrote: 
> Brian J. Murrell wrote:
> > I'm just starting to experiment with multi-isp configuration and at the
> > part of the doc (http://www.shorewall.net/MultiISP.html) that specifies:
> > 
> >         Regardless of whether you have masqueraded hosts or not, YOU
> >         MUST ADD THESE TWO ENTRIES TO /etc/shorewall/masq:
> >         
> >         #INTERFACE       SUBNET            ADDRESS
> >         eth0             130.252.99.27     206.124.146.176
> >         eth1             206.124.146.176   130.252.99.27
> > 
> > If this is a MUST requirement for all multi-isp set ups, then can
> > shorewall not figure this out for itself and install it without the user
> > having to specify it?
> 
> Not really.
> 
> a) Shorewall couldn't determine where to put them in the masq file and the
> file is order-sensitive.

OK.  That brings up a question then: where should they go normally?  It
seems that they are just a safety check that a locally generated packet
has the right source address for the interface it's bound for.  Does
order really matter in this case?

Given the configuration at hand at
http://www.shorewall.net/MultiISP.html:

#INTERFACE SUBNET ADDRESS 
eth0             eth2              206.124.146.176
eth1             eth2              130.252.99.27

and the need to add:

eth0 130.252.99.27 206.124.146.176 
eth1             206.124.146.176   130.252.99.27

It doesn't seem to matter what order those go in since they don't
overlap at all.

> b) Shorewall could redundantly add them, not realizing that the same traffic
>  is adequately covered by other masq rules such as:
> 
>       eth0    0.0.0.0/0       206.124.146.177 #The different ADDRESS is
>                                                 #intentional

If the "don't use the other known interface source addresses" rules were
put right at the end, would that not suffice?  i.e:
      * if no other masq rules match and 
      * the source address for the destined interface is known to be for
        another outbound interface
              * then masq it to the right address

In any case, I am sure you understand the issues better than I, so if my
logic above is still flawed, I will just accept that it cannot be made
automatic.

I have some thoughts on dealing with dead ISPs and multi-ISP
configurations.  Shall I start a thread about it or are you really not
interested in Shorewall dealing with this situation?

b. 

-- 
My other computer is your Microsoft Windows server.

Brian J. Murrell

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