RE: Multihoming by IP Layer Address Rewriting (MILAR)

[Iljitsch van Beijnum <iljitsch@muada.com>]

On Tue, 4 Sep 2001, Michel Py wrote:

> >> Note that a network that is part of the DFZ does not have "an ISP".

> An interesting semantics issue. To me, an ISP is who provides
> connectivity to the Internet.

Can't argue with you there. Now let's define "default-free zone". I would
say: "the subset of routers that do not receive a full routing table from
a single peer or a default route".

> In the US, it is fairly common to buy a DS3 or bigger
> pipe with full BGP feed from one or more ISP(s) (that would be for
> companies that have an ASN and a CIDR block).

Having an AS number and a PI or even PA block don't make a network part of
the DFZ: as long as it pays another network to carry packets to any
destination, the network in question may use a default to the other
network and if there is a default filtering is possible without hurting
connectivity. The problem with the DFZ is that defaults are not possible,
so filtering always hurts connectivity.

> >> you pay an ISP to route traffic to all destinations connected to the
> >> Net

> I don't think so. I pay my ISP to provide me a connection to the
> backbone

"backbone" is a word without meaning in interdomain routing.

> without the hassle of getting into a colo

Why would your location have anything to do with it?

> >> in other words: you pay for a default.

> No, I'm getting a full BGP feed.

A full feed is pretty much a more verbose default.

> >> (but the reverse is not always true: a network running without a
> >> default is not necessarily part of the DFZ)

> Agree. A network is part of the DFZ because it has its own block, the
> same animal that clogs the DFZ's routing table.

No, that's my point: that has still nothing to do with it. Having your own
block means you are visible in the DFZ, being part of the DFZ means you
can't dump packets for which you don't have a route in someone else's lap.
In other words: the DFZ is the top of the tree. On all other levels, you
route the packet to a known destination or to the higher level. At the
top, there is no higher level so all destinations have to be known
destinations to be reachable.

> >> Any consensus on BGP changes is a long way off

> Definitely. I guess I have not made myself clear about the relation
> between
> MHTP and BGP. What should I change in 6.2.9 of
> http://arneill-py.sacramento.ca.us/draft-py-multi6-mhtp-01.txt ?

Nameserver problem, can't get at the document right now. Maybe you should
multihome...

Iljitsch