Re: [LARTC] policy routing at its best

[Tomas Bonnedahl <tomas@yes.nu>]

i have some additional information regarding this issue with policy routing.

on the router that has policy routing implemented, read further down for 
more information on my gols, three ethernet interfaces exists.

since the routing table 'main' just consists of a route to 192.168.1/24
with a prohihbit 0/0, you cannot from the router reach a network 
that is located on some of the other interfaces than 192.168.1/24 exists
on. this is because the src address in the packet will be the address of
that interface which the packet will exit. according to the rules that exists
in the RPDB, that address will use the routing table 'main' which, in turn,
does not have a route to that network. 

the solution to this would be to:
1. make (two) rules which says "if the src address of a packet is the adress
of an interface, use table 'all'". (also note that im using the /32 address)
2. add, in routing table 'main', routes to these /32 addresses.

the first part here is used so that a packet could be _sent_ away correct, the
second part is used so that a packets can come _back_ correct.

im sure martin have some insight in this, perhaps a simpler solution?

indeed, i did not think of this when implementing policy routing since i was 
only concerned with networks and not the router itself.

i hope this will help someone struggeling with policy routing.


best regards,
tomas bonnedahl

On Thu, Mar 06, 2003 at 04:31:42PM +0100, Tomas Bonnedahl wrote:
> hello list (and martin) ;x
> 
> i have now composed my final(?) policy routing design.
> 
> the goals i had when beginning with this, for you that have not follow
> mine and martins thread, was to 1) only let 192.168.1/24 to see all routes,
> 2) not route between defined networks, except to and from 192.168.1/24 and 3) not 
> defined networks should only be able to reach 192.168.1/24.
> 
> this might sound simple. it wasnt for me.
> 
> the solution i came up with, after days and days of thinking (and patience) was
> this:
> 
> two routing tables, one called "ALL" that, suprisingly, held routes to all networks defined
> and a default route to internet. the other called "main", just for ease, that held one route to 
> 192.168.1/24 and had a default prohibit.
> 
> the one rule that exists just says "if src = 192.168.1/24 use table ALL". of course there is
> an additional rule, the standard one that says "from all lookup main" with a number of 32766.
> 
> so, for you that doesnt understand my poor english, literally every network that passes, except
> from 192.168.1/24, will use the main table that just holds the route to 192.168.1/24 and the 
> prohibit one.
> 
> 
> this so simple, something just has to be wrong. feel free to englighten me.
> 
> 
> please flame.
> 
> best regards,
> tomas bonnedahl
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