two public ip addresses on one interface

[Julian Elischer]

Wilkinson, Alex wrote:
>     0n Mon, May 28, 2007 at 11:43:21AM +0400, Eygene Ryabinkin wrote: 
> 
>     >Alex, good day.
>     >
>     >Sun, May 27, 2007 at 07:07:41PM +0800, Wilkinson, Alex wrote:
>     >>     > If your aliases are part of the same subnet as the "primary" or first configured IP, then you want to 
>     >>     > use the all-1's netmask.  In your case, however, the second IP is part of a completely different subnet, 
>     >>     > and you can (and should) use a /24 netmask....
>     >> 
>     >> I have always wondered why we need to use the "all-1's" netmask. Why is this ?
>     >
>     >Because if you're stuffing two addresses from the same subnet to
>     >one interface it will not work: there can be only one route to the
>     >specified network in the FreeBSD routing table.  And adding IP to
>     >the interface creates the entry in the routing table.  So you should
>     >specify the different mask and most probably 0xffffffff will be the
>     >best choice, but your mileage may vary with your routing needs.
> 
> mmm ... it looks like you can actually get around this on OpenBSD 4.1
> with their new "multiple routing table" code.
> 
> "Multiple routing tables. What does it mean for PF?
> 
>   Henning Brauer:
>   The kernel used to have one routing table per address
>   family--one for inet, one for inet6, one for IPsec, usually. Now it can have
>   multiple tables. From within PF, you can select which routing table should be
>   used for the route lookup later--you can implement policy routing with this. But
>   much more could be done--this is really only the groundwork. It could be
>   possible, in future, to have overlapping address ranges on interfaces and place
>   interfaces into different routing tables, forming a kind of virtual routers. And
>   of course, the routing daemons will learn to make more use of alternate
>   tables."

the trouble I have with this is that by the time pf or ipfw get to the packet,
the  routing has already been done.


> 
>  [http://www.onlamp.com/pub/a/bsd/2007/05/03/openbsd-41-puffy-strikes-again.html?page=2]
> 
>  -aW
> 
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