In the referenced message, Ralph Doncaster said:
> > And your assumption about my Ottawa-Toronto link is wrong. I have a 100M
> > point-to-point ethernet link between the cities. I have a 100M transit
> > connection to Peer1 in Toronto, and have issued a letter of intent to a
> > transit provider in Ottawa for a 100M link.
> Ralph, if you have a 100m link between the two cities, why don't you use
> conditional announcements to only announce your /20 though Ottawa if your
> primary transit in Toronto goes down? Then, you only need to announce your
> /20 in Toronto, no need to deaggregate, and the whole issue is solved.
> Then, when you have the Ottawa 100m transit link up, you can announce your
> /20 to both transit providers all the time.
That is roughly the intention. I also have to be able to announce the
more specifics for when the Ottawa-Toronto link goes down. You could find
in the archives my posts from a couple months back asking how to do this.
A partitioned AS is an error condition. The correct solution (and the only
one which will work in the DFZ) is to make certain your AS is never
This can be done with either redundant intra-as links, or via tunnels
constructed between the routers facing your transit.
The latter creates a logical redundant link, on which you place a
higher igp metric than the corresponding path across normal intra-as
links. This is a solution that many well-engineered small networks
have used in the past, to prevent AS partitioning.
Both are solutions which don't require more-specifics to function.