Lesson 4 - AS relationships and interdomain routing Flashcards
What is AS
An Autonomous System (AS) is a group of routers (including the links among them) that operate under the same administrative authority. Each AS implements its own set of policies, makes its own traffic engineering decisions and interconnection strategies, and also determines how the traffic leaves and enters the network.
What kind of relationship does ASes have with other parties?
provider-customer - providers charge for traffic
peer relationships - share traffic
What is BGP
Border Gateway Protocol (BGP) is a standardized exterior gateway protocol designed to exchange routing and reachability information among autonomous systems (AS) on the Internet. The protocol is classified as a path vector protocol.
Which rules does BGP policy follow for importing rules?
The routes that are preferred first are the customer routes, then the peer routes and finally the provider routes.
AS: a) wants to ensure that routes towards its customers do not traverse other ASes unnecessarily generating costs, b) uses routes learned from peers since these are usually “free”
Which rules does BGP policy follow for exporting rules.
Likely foward client tables to everyone.
Likely forward peers and providers tables to clients.
The AS would avoid forwarding a route not used by a client because it would be allowing unwanted and unpaid traffic to go through its network.
What are the design goal of BGP?
Scalability - manage design growth of internet
Express routing policies
Allow cooperation among ASes
Security
Explain BGP protocol basics
To begin a BGP session a router will send an OPEN message to another router. Then the sending and receiving router will send each other announcements from their individual routing tables.
After a session is established between BGP peers, the peers can exchange BGP messages to provide reachability information and enforce routing policies.
What is the difference between iBGP and eBGP?
eBGP is responsible for transmitting router informatioin of border routers of adjacent ASes about external destinations.
iBGP is responsible for disseminating BGP route advertisements about external destinations to routers inside the AS.
What is the difference between iBGP and IGP-like protocols (RIP or OSPF)?
iBGP routes inside the AS to external destinations.
IGP routes inside the AS to internal destinations.
How does BGP decision process to select routes at a router work (in a nutshell)?
Mostly BGP policicy prefers routes in this order:
- Local routes
- shorter routes
- Lower MED (Multi-exit descriminator)
- Shortest IGP path
- Tiebreaker with ID or reliability.
The router goes through the list of attributes in the route advertisements and compares the attributes to it’s policy.
What are 2 main challenges with BGP? Why?
misconfigurations
faults
What is an IXP?
IXPs are physical infrastructures that provide the means for ASes to interconnect and directly exchange traffic with one another.
What are the 4 reasons of IXPs increased popularity?
- IXPs are interconnection hubs handling large traffic volumes
- Important role in mitigating DDoS attacks
- “Real-World” Infrastructures with a pleathora of research opportunities
- IXPs are active marketplaces and technology innovation hubs
Which services do IXPs provide?
- Public peering
- Private peering
- Route servers and service level agreements
- Remote peeing through resellers
- Moblie peering
- DDoS blackholing
- Free value-added services
What are the differences between Multi-lateral and unilateral peering at IXPs?
Go find out.
