Route reflectors aren't the only way
that we can manage the iBGP full mesh scalability problem.
There's also something called confederations.
Confederations allow us to take our whole autonomous system
and break it down into smaller autonomous systems
that work together.
You could kind of think of it like breaking down
a prefix in two subnets.
And just like there are public IP addresses and private IP
addresses, there are also public autonomous system numbers
and private autonomous system numbers. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
and private autonomous system numbers.
So when we have a public autonomous system,
like autonomous system 300, and we
want to break that down into smaller autonomous systems
that service autonomous 300, we could actually
use private autonomous system numbers
to build up our confederation.
Let's jump on a whiteboard.
And that way, you can see how it really looks.
Now what we're going to do is we're
going to shift our view towards this section of the topology.
We've been working down here in AS 100 and 200 for a while now.
Now we're going to work with 200, 300, and 400. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
Now we're going to work with 200, 300, and 400.
And you can see in AS 300, we have five routers running here.
They're all running iBGP at this instance.
But rather than build a full mesh towards everybody
here and make this big, really ugly, messy,
multiple connections section thing going
on here, what we can do, actually,
is we can build what's called a confederation.
We're going to split our autonomous system right here
into two autonomous systems.
And this is when we would use the private autonomous system WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And this is when we would use the private autonomous system
numbers.
Those numbers are 64,512 through 65,535 for the 16-bit
autonomous systems, or for the 32-bit autonomous systems,
this goes from 4,200,000 to 4,200--
oh, I got to Google this one more time--
4,294,967,295. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
4,294,967,295.
These are the 32-bit private AS numbers.
So in this case, we have an autonomous system
here labeled 65,100 and an autonomous system
here labeled 65,200.
Now this begs a lot of questions about how confederations really
work when it comes towards peering.
The first thing that we'll say is that AS 400 here
and AS 200 here have no idea that they are
peering with a confederation.
From their standpoint when they peer right here WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
From their standpoint when they peer right here
in on these links, they are peering with AS 300.
These routers here know that they
are in a confederation that is also representing AS 300.
So really what this means is when a route comes in
from AS 400 and it gets sent out to AS 200,
AS 200's path, it's AS path, is going
to be 300, 400, and internal.
Within AS 300, within these confederations,
however, the path will have a parentheses, WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
however, the path will have a parentheses,
and it will show the confederation path
that it took to get there--
something like that.
So in this case on this router, it went through AS 65,200
and then to AS 400.
Ultimately, what this means is that we
can manage how many BGP sessions are actually
peering with each other by minimizing how many sessions
are needed.
Now only these two routers need to have a session,
and these two routers can have a session, WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
and these two routers can have a session,
and then these three routers need
to have a session to each other.
And what's really cool is, right here,
we can actually use this as a route reflector.
So in this scenario here, AS 400 would advertise [INAUDIBLE],,
and this router would think it's an eBGP peer.
It would then send it outbound towards its iBGP peer,
as well as up to its confederation peer.
The confederation peer would kind of
think of it as an eBGP advertisement,
so it would send it onto this router. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
so it would send it onto this router.
And maybe this router is serving as a route reflector
where its client is here.
So because it received this route from a non-client peer,
it would forward it onto this router.
And because there is an eBGP relationship here,
this router would forward it on out.
Isn't this all fantastic and amazing?
Well, we're going to jump into the virtual lap
and configure in the very next Nugget.
In the meantime, this has been how to break down an autonomous
system into a confederation.
I hope this has been informative for you, WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
I hope this has been informative for you,
and I'd like to thank you for viewing.