Re: A tunneling proposal

[Ramakrishna Gummadi <ramki@cs.berkeley.edu>]

On Tue, 17 Jul 2001, Iljitsch van Beijnum wrote:

> On Mon, 16 Jul 2001, Daniel Senie wrote:
>
> > >One can think of a simple extension to tunneling under such ISP-wide
> > >outages---if tunnel creation fails, the second ISP initiates
> > >non-aggregatable route announcements for the prefixes from the address
> > >space of the first ISP who has become unreachable.
>
> Speaking from operational experience: this is not going to work. As a
> multihomed site, I have to regularly check if I can still reach the entire
> internet when one line goes down, because it wouldn't be the first time
> someone placed the wrong filters at the wrong place. If you don't test
> something like this, it's not going to work when you need it.

In this case, at least, I don't see a big scalability problem as long as
everyone tests randomly, and the routers forward using longest prefix
match.

>
> Also, when huge amounts of more specific prefixes appear, this could be just
> the kind of thing to drive a lot of routers over the edge, especially when
> we're getting close to a common limit, such as 128 MB in Cisco routers.

It may be useful to know what % of current router memory each ISP
currently uses, and how many networks he aggregates. That should give a
back-of-the-envolope figure about how much a single ISP can overload a
network. While, clearly, this figure will be much better than what is
today (assuming every multihomed site today is advertising
non-aggregatable routes into the DFZ, and there is no one major ISP
serving all multihomed sites), it may give a better idea of the rough
number of possible excess routes that can appear due to a single ISP
breakdown.

>
> And when you can announce more specifics some of the time, why not make
> "some" "a lot" or even "all"? And then people will start to filter and we're
> back to square one.

I think we can safely assume that the probability of the event of an
entire ISP going down is randomly distributed across time, which means
that even if one ISP goes down completely, the overload will be less than
that in the case where every ISP advertises non-aggregatable routes (as is
the current case today).

thanks,
ramki