Sunday, April 14, 2019

Joe's Internet -- Addressing and Interconnection

In the last installment, Routing Policy -- interconnecting with other networks, we talked about the business relationships Joe's Internet (J-Inet) might have with other networks.  Now we'll look a little closer at the technical side of how those relationships are enacted on the network itself.

Before we get too much closer to J-Inet, I want to point out that I'm going to be using a single network model for continuity between posts.  I've worked out IP addressing (v4 & v6), consistent routing policies, and a topology that should suffice for many posts. I've got several posts lined up that should help show at least one path to building a scalable network.

The Interconnects

J-Inet has two transit providers (Transit 1 & 2), three customers (Customer A, B, & C), and a single Peer (Peer 1).  Customer C is a bit of stretch for this conversation.  They aren't an autonomous system, but we'll look at them anyway, as it may lead some readers to revelations they might not have otherwise.

J-Inet has four Points of Presence (POPs) where equipment is housed.  Most customers of J-Inet are like Customer C.  They simply buy transit from J-Inet.  These customers actually make up the bulk of J-Inet's revenue.  But they're pretty boring from an network perspective.

The Network, Prefixes, and Policy

The network itself is pretty simple, and looks like this:
Joe's Internet -- Simple Map
Over view J-Inet's network and interconnects.  Click on it for more detail

J-Inet has two blocks of address space it uses internally, that we will advertise to anyone that interconnects.  Those prefixes are: and

Customer A uses  That block comes from J-Inet's prefixes, but they are allowed to use it as long as they are a customer of J-Inet.  J-Inet also allows Customer A to advertise this prefix across any interconnects they may have with other networks.  J-Inet will pass all of the prefixes it knows about to Customer A.

Customer B uses, which was allocated to them from their Regional Internet Registry.  They advertise this prefix to us, and any other interconnects they have according to their own routing policy. J-Inet will pass advertise all routes to Customer B.

Customer C uses  They don't have any other interconnects, so they aren't really an autonomous system (AS).  They're in this mix as a kind of anti-example -- a customer that really only acts as an extension of J-Inet's network and routing policy.  Neither Customer C nor J-Inet will advertise prefixes to one another.

Peer 1 is another ISP that happens to have equipment in the same building that houses POP 1.  J-Inet and the Peer 1 decided that they should interconnect directly.  They will be announcing to J-Inet.  J-Inet will pass internal and customer prefixes to Peer 1, but will not send any routes learned from transit providers.

Transit 1 and Transit 2 are networks that have customers and other interconnects.  Since they are transit providers, they have promised to get traffic to any destination. However, they bouth announce prefixes to us, J-Inet can make an informed decision about which network should be used for any given prefix.  J-Inet will announce internal routes and customer routes to both transit providers.  J-Inet will not advertise routes learned from Peer1.  Lastly, J-Inet will not advertise any transit routes back to either transit provider.  (i.e. J-Inet will not allow transit to the these providers.)

At this point, we have a pretty good idea of J-Inet's network topology and how it interconnects with customers, peers and transit providers.  In our next installment, we'll look at some of the internal housekeeping of J-Inet's network is put together, and later use this internal configuration to make our interconnects simpler.

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