Common View of the Telco Network
Common View of the IP Network (Layer 3)
What This Course Is About
Forwarding vs. Routing
What You Should Take Away
Anthropology of Routing
Routing can happen at any level
IP is a Network Layer Protocol
All Hail the IP Datagram!
IP Hour Glass
Routers Talking to Routers
Architecture of Dynamic Routing
"Topology information is flooded within..."
The Gang of Four
Autonomous Routing Domains (ARDs)
Autonomous System (AS) Numbers
Autonomous Routing Domains Don’t Always Need BGP or an ASN
ASNs Can Be “Shared” (RFC 2270)
ARD != AS
How Many ASNs?
How many prefixes?
A Bit of OGI’s AS Neighborhood
Partial View of cs.wisc.edu Neighborhood
Policy : Transit vs. Nontransit
Customers and Providers
The “Peering” Relationship
Peering Provides Shortcuts
Policy-Based vs. Distance-Based Routing?
Why not minimize “AS hop count”?
Four Types of BGP Messages
Attributes are Used to Select Best Routes
BGP Route Processing
Route Selection Summary
Shorter Doesn’t Always Mean Shorter
BGP Routing Tables
AS Graphs Depend on Point of View
AS Graphs Can Be Fun
AS Graphs Do Not Show “Topology”!
So Many Choices
Implementing Backup Links with Local Preference (Outbound Traffic)
Shedding Inbound Traffic with ASPATH Prepending
… But Padding Does Not Always Work
COMMUNITY Attribute to the Rescue!
Don’t celebrate just yet…
Customer installs a “backup link” …
The primary link is repaired, and something odd occurs…
WAIT! It Gets Better…
What the heck is going on?
Are we too complacent?
Let’s look at “te” communities…
Some AS286 Communities
Need “Semantics of Interdomain Routing”