Computer Networks · free preview
The Global Internet
Scaling routing to a planet requires hierarchy twice over, inside a domain link-state areas confine flooding to regions with border routers summarizing routes to the backbone area, between domains the Internet is a graph of autonomous systems each under one administration and free to run its own interior routing, and interdomain routing speaks the Border Gateway Protocol, which advertises only reachability with complete paths of autonomous system numbers, prevents loops by rejecting any path containing oneself, and exists to express policies, preferring providers, refusing transit, keeping economics private, that no metric could encode.
1. Hierarchy Inside the Domain
Hierarchy Inside the Domain
2. A Network of Networks
A Network of Networks
3. The Border Gateway Protocol
The Border Gateway Protocol
4. The Shape That Emerged
The Shape That Emerged
5. The area border
In a domain split into link-state areas, what does an area border router do?
6. Why autonomous systems
What problem does dividing the Internet into autonomous systems solve?
7. Path as loop detector
How does BGP prevent routing loops without a time-to-live on its advertisements?
8. Stub and transit
A multihomed company connects to two providers for reliability but refuses to carry traffic between them. How is that refusal expressed?
9. Reachability not quality
Why do BGP advertisements announce only that a prefix is reachable, without any cost or quality metric?
10. When aggregation holds
A provider wants to advertise one prefix covering two thousand customer networks. What must be true for that to work?
11. Area zero
In hierarchical link-state routing, what is the special backbone area, to which all other areas must connect, commonly called?
12. Path vector
BGP is classed as what kind of routing protocol, named for its habit of carrying the complete list of traversed autonomous systems?
13. Withdrawal
What does a BGP speaker send to retract a previously advertised route that is no longer valid?
14. Policy secrecy
Interdomain routing policies are often kept private because they encode the operators' what, which competitors must not see?
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