Table of Contents
Exterior Routing 201
Agenda
What is the Problem to be Solved?
PPT Slide
PPT Slide
ISPs Facing End User
Before the Animals
Load the Ark
Quirks, Definitions and Issues
I said "peer," not "peer"
PPT Slide
Closest Exit Routing Hot potato
Asymmetrical Routing
ISP Scenarios
Basic Internet Access ISP
Bilateral Peering
Large Content Provider
Multilateral Peering
Special Case: Local Exchanges
POP and Other Internal Design
Typical Basic POP Implementation
Transit Provider POP, Intra-POP
POP Confederations
POP Reflectors
Open Access/Specialized Access
Tunneled Addressing
Router Requirements
Routing Paradigms
Observations on Routing Table Size
Growth in Global Routing Table Size
Growth in Typical Tier 1 Routing Table Size (external + customer, not infrastructure)
Observation: More than Routes
Convergence
Single Router Convergence
Distinguish among cases
S-T-R-E-T-C-H
Joining the Club
More than Just Addresses, Protocol...
Complexity
PPT Slide
Operational Relationships 1 Addresses and Delegation
Obtain routable address space
Origination vs. Advertising
Aggregating your Own Traffic
Advertising with NO-EXPORT
Aggregation is better than Aggravation
Preparing for Address Request (1)
Prepare for Address Request (2) An ISP Topology
Establishing an AS (1) AS Number Request
Establishing an AS (2) Registering in Routing Registry
Establishing an AS (3) Operational deployment
Routing Registry Objects
Operational Relationships 3: Registries, Domains, etc.
Autonomous System
Current AS Definition RFC 1930
AS Number
Operational Relationships 2: Addesses and Autonomous Systems
Full Employment for Consultants: Policies are inside Routers
Stop! What are you going to Advertise?
Advertising Affects
Routes Eligible to Advertise
Stop! What are you going to Accept?
Do Not Accept
Turning it On
BGP Configuration Overview
Policy Implementation Flow
Policy vs. Protocol Flow
BGP Configurations
Router ID and loopback interface
Refining the Configuration
The BGP Tunnel
Load Balancing 1: IP Level to Single Provider Router
Load Balancing 1: Multiple Routers
Another Non-BGP Alternative OSPF Routing Domain
Multiple OSPF Defaults
Blackhole Route
Effects of Blackholing
BGP Path Selection
Next Hop Access
Scope: MED vs. Local Preference vs. Weight
Administrative Weight (Cisco extension)
Weight example for load sharing
Tiebreaker for Equal Weight: Local Preference
Local Preference example for load sharing
Prefer locally originated routes
AS Path
Shortest AS Path (Cisco extension)
Full Employment For Consultants: Interpreting AS Path
AS Path Prepending
Limitations of Prepending
External Paths Preferred
Lowest MED
Full Employment For Consultants: Weight, Local Preference & MED
Full Employment For Consultants: Scope of MED
Closest Neighbor
Lowest BGP router ID
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