Re: [mif] Annoncing new draft: draft-kaiser-if-sel-00

[Lorenzo Colitti <[e-mail]>]

On Tue, Jun 18, 2013 at 6:20 AM, Arnaud Kaiser <[e-mail]> wrote:

> This document describes an interface selection mechanism that enables
> multiple interfaces (multihomed) IPv6 hosts to select their most
> appropriate egress interface to send data over the network. The
> mechanism extends the Neighbor Discovery (ND) protocol [RFC4861] with
> two new Router Advertisement options.
>
> The interface selection is based on the metric considered in the network:
> routers provide informations to hosts about the cost of the links and the
> total cost of specific routes (upon hosts requests). Using these
> informations hosts select their outgoing interface leading to improve the
> end-to-end routing.
>

A couple of comments:

1. It appears that you are proposing that whenever a host wants to send a
packet to a new destination IP address, it must first send a packet to all
the routers on the link asking them what the cost of talking to that
address is.

This behaviour is a big change to how IPv6 communication works, because
nowhere in IPv6 (or in IPv4, either) do we talk to routers before sending
packets. A change of that magnitude should go through careful review by
6man before it is made.

Also note that such a change can have very substantial impact to end-to-end
latency (think cell network, where the router is at least 20ms away) and
scalability (think enterprise network, with 5000 clients on the same
router), and opens up the possibility of DoS attacks on the router. I don't
think this is a good idea.

2. The proposal says that all RAs MUST contain the new link cost option.
What happens when it does not? Even if all the routers in the world
immediately adopt this option, what about routers that have not been
updated?

3. A host can in general be connected to different networks operated by
different entities (think home wifi and cell network). If those two
entities do not have a prior agreement, how does it work? They could each
pick different costs, or pick the "wrong" costs. What if they have the same
costs?