Anonomous systems

Question 1

why AS?

Answer 1

to group routers into regions so that each region can control their own domain routing policies and such

Question 2

inter vs intra domain

Answer 2

Inter:
- routing between ASes
- more conserned with the routing polices

Intra:
- routing within a AS
- single policy
- more concerned with performance

Question 3

Stub

Answer 3

• AS that is only connected to 1 other AS
• usually for end users or customers

Question 4

multihomed

Answer 4

• AS that is connected to more than 1 other AS

Question 5

transit

Answer 5

• a multihomed that allows traffic to transit through

Question 6

non-transit

Answer 6

• a multihomed that does not allow transit traffic

Question 7

what is BGP

Answer 7

• protocol that holds internet together

Question 8

eBGP

Answer 8

• used in inter-domain routing
• updates from one AS to antoher

Question 9

iBGP

Answer 9

• used in Intra-domain routing
• propagates updates within the AS

Question 10

BGP session

Answer 10

2 BPG routers exchanging BGP messeges

Question 11

BGP update

Answer 11

a path advertisment

Question 12

what if a BGP router gets multiple paths to same dest?

Answer 12

chooses based on policy

Question 13

what if a inner router can choose mult gateways to get to dest?

Answer 13

picks one with least intra-domain cost

Question 14

BGP process

Answer 14

1) exchange BGP updates
2) clean the updates with policy
3) update local routing table
4) adverstise to others

Question 15

routing vs forwarding

Answer 15

routing:
- control plane
- route from src to dest

forwarding:
- data plane
- from incoming interface to outgoing interface