BGP Border Gateway Protocol EE122 Section 3
BGP
Jan 23, 2016
BGP. Border Gateway Protocol. EE122 Section 3. Border Gateway Protocol. Protocol for inter-domain routing Designed for policy and privacy Why not distance-vector? Shortest path may not be policy-compliant …and policies vary across domains! Why not link-state? - PowerPoint PPT Presentation
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BGPBorder Gateway Protocol
EE122 Section 3
Border Gateway Protocol
• Protocol for inter-domain routing• Designed for policy and privacy• Why not distance-vector?– Shortest path may not be policy-compliant– …and policies vary across domains!
• Why not link-state?– Everybody knows everything – privacy goes for a
toss!• Enter path vector!
BGP: Path Vector
1 2
0
A B
A: 1 B: 2
A: 1 B: 2
BGP: Path Vector
1 2
0
A B
B: 0 2 A: 0 1
A: 1 B: 2
A: 0 1B: 0 2
BGP: Path Vector
1 2
0
A B
A: 1B: 1 0 2
A: 2 0 1B: 2
A: 0 1B: 0 2
BGP: Path Vector
1 2
0
A B
A: 1B: 1 0
A: 2 0 1B: 2
A: 0 1B: 0 2
Withdrawal - B: 0 2Advertise - B: 0
A: 0 1B: 0
BGP Relationships
• Provider -> Customer:• Peer <-> Peer:
1 2
0
A B C
A: 1B: 1C: 0 1
A: 1 2B: 2C: 0 2
A: 1 0B: 1 0C: 0
It’s all about the money!
• Customer pays provider• Peers don’t pay each other – Assume equal flow both ways
• Routing policies try to minimize payment
Packets flow where money flows
• Route Selection– Preference Order: Customer > Peer > Provider
• Route Export Policy– Peers provide transit between their customers– Peers do not provide transit to each other
Route Selection: Customer > Peer
• Provider -> Customer:• Peer <-> Peer:
1 2
0
A B C
A: 1B: 1C: 0 1
A: 1 2B: 2C: 0 2
A: 1 0B: 1 0C: 0
Route Selection : Peer > Provider
• Provider -> Customer:• Peer <-> Peer:
1 2
0
A B C
A: 1B: 1C: 0 1
A: 1 2B: 2C: 0 2
A: 1 0B: 1 0C: 0
Route Selection : Provider (no choice)
• Provider -> Customer:• Peer <-> Peer:
1 2
0
A B C
A: 1B: 1C: 0 1
A: 1 2B: 2C: 0 2
A: 1 0B: 1 0C: 0
Packets flow where money flows
• Route Selection– Preference Order: Customer > Peer > Provider
• Route Export Policy– Peers provide transit between their customers– Peers do not provide transit to each other
Route Export policy: Advertise customers
• Provider -> Customer:• Peer <-> Peer:
1 2
0
A B C
A: 1B: 1C: 0 1
A: 1 2B: 2C: 0 2
A: 1 0B: 1 0C: 0
BGP Routing Game!
• No talking! Communicate via pieces of paper• Route selection precedence– Customer > Peer > Provider
• Export policy: Advertise customers• Message format:– Withdrawal - <host network>: <path>– Advertise - <host network>: <path>
• Goal: Reach steady state
AS 0
3 4
0
A B C
1 2A: 0B: ?C: ?
3 4
0
A B C
1 2A: ?B: ?C: ?
AS 1
3 4
0
A B C
1 2A: ?B: ?C: ?
AS 2
3 4
0
A B C
1 2
A: ?B: 3C: ?
AS 3
3 4
0
A B C
1 2
A: ?B: ?C: 4
AS 4
Initial State
3 4
0
A B C
1 2A: 0B: ?C: ? A: ?
B: ?C: ?
A: ?B: ?C: ?
A: ?B: 3C: ?
A: ?B: ?C: 4
3 4
0
A B C
1 2A: 0B: 0 3C: 0 2 4 A: 1 0
B: 1 3C: 1 2 4
A: 2 0B: 2 1 3C: 2 4
A: 3 0B: 3C: 3 4
A: 4 2 0B: 4 3C: 4
Steady State
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