RE: RE: Policy based ISP selection - Redirects

["Tony Hain" <alh-ietf@tndh.net>]

Marcelo wrote:
> There are some issues when using redirect,i believe.
> The main problem that I found is that redirects must be with
> local scope. This implies that the first hop must redirect
> the packet to the correct ISP.
Yes a redirect must be to another router on the local link. In your drawing
this is the case, but it is clear from this note you are looking at a
different problem.

> Then , if there are several sub-networks in the site, all the
> routers must know when to send the redirects.
No, all the routers must know the routing policy, but that is their role in
life. Also as you note redirects are only applicable on link.

> This last statement means that:
> - All the routers must inspect the port information in all
> the packets which may arise some performance issues
> - All the routers and all the hosts must know the policies,
> which makes management more complex
Routers already need to know routing policy, so it is the desire for some
host to have a different policy that adds complexity.

> In the case that routing headers are used, only hosts must
> have policies knowledge
Overriding the routing policy of the underlying infrastructure is the reason
the routing header was created. In general the use of a routing header has
nothing to do with address selection rules. Even if you tried to tie them,
there is nothing preventing policy at host B to override that by using a
routing header to cause all of its packets to be sent through ISP-B.

Tony