04/05/20011 ecs298k: Routing in General... lecture #2 Dr. S. Felix Wu Computer Science Department University of California, Davis wu

04/05/2001 1

ecs298k:Routing in General...lecture #2

Dr. S. Felix Wu

Computer Science Department

University of California, Davishttp://www.cs.ucdavis.edu/~wu/

[email protected]

2 04/05/2001

Routing Protocol Framework Information Model

FIB

RIB

NPDU Header (Network Protocol Data Unit)

(Dest, NextHop, Routing Metrics)

Forwarding Algorithm

OSPF

RIBRIB

RIPv2 BGP4

FIB

ForwardingDecision

Application Layer

Network Layer

RoutingInformationBase

ForwardingInformationBase

04/05/2001 3

Operation Model - Routing Information Exchange

Hey, Here is the routing information I got so far

Hmm, some of them are obsolete, Here is my update

04/05/2001 4

Operation Model - Route Generation and Selection

Which algorithm should I use??Distributed Dijikstra’s algorithm or

Distributed Bellman-Ford algorithm?

Routing Information Base

Forwarding Information Base

application Layer

network Layer

04/05/2001 5

Routing Protocol Framework Topology Model

Administrative Domain 1 Administrative Domain 2

ASBR

ASBRASBR

AIR

Routing Domain Domain

HostAIRHost

AIRAIR

Host

Host

Routing Domain Domain

AIR

Two Level Routing - Intra-domain and Inter-domain Multiple routing domains can form an administrative domain ASBR and It’s restriction Routing protocol examples ( RIP, RIPv2, IGRP, OSPF, EGP, BGP, IS-IS)

04/05/2001 6

FIB• Forwarding Information Base

• Longest Matching Rule– CIDR (Classless Inter-domain Routing)

• IP address + Net Mask Length• 128.32.12/24 versus 128.32.12/22

– 10000000.00100000.00001100.--------– 11111111.11111111.11111111.00000000– 11111111.11111111.11111100.00000000

– Aggregation:• 128.32.12.0/24, 128.32.13.0/24 => 128.32.12.0/23• 128.32.12.0/23, 128.32.14.0/23 => 128.32.12.0/22

04/05/2001 7

IP Routing

• Routing targets network addresses– Clouds - IP network address.

• Routers use forwarding table– destination/mask, next hop, network interface, metric– table look-up for each packet– need to recognize address structure

• Routing information updates the forwarding table after the route computation.

04/05/2001 8

Routing

I want to knowthe shortest pathor simply “a path”

Routers exchange local information!

SRC

DST

04/05/2001 9

Link State

A

B

C

You

YourNeighbor

A B

A B

A B

Flooding

04/05/2001 10

04/05/2001 11

Link State

A

B

C

You

YourNeighbor

A B

A B

A B

Flooding

04/05/2001 12

Distance Vector

A

B

C

You

YourNeighbor

A: 3 hopsB: 2 hopsC: 2 hops

Your Neoghbor will decide who should be the next hop!

A: 1 hopB: 2 hops

VIEW

04/05/2001 13

Routing Information

• Link State:– I let the whole world knows about my

relationship with my neighbors.– (Felix, Neighbor-X) is up!

• Distance Vector:– I let all my neighbors knows about my

relationship with the rest of the world.– (Felix can get to Remote-Y) in 5 hops.

04/05/2001 14

RIP• Routing Information Protocol is a simple

distance vector protocol.

• Initialization:– When the routing daemon is initialized, it send

a request command to each network interface (card).

– Neighboring routers will reply with routing table information.

04/05/2001 15

RIP, cont.

• Periodic Updates– routers advertise tables with neighbors

periodically (~30 seconds) + upon interface changes.

• Split-Horizon– Router records the interface providing a route

and does not propagate it back.

04/05/2001 16

Bad News Propagation: 1

A: 0 A: 1 A: 2 A: 3 A: 4 A: 51 1 1 1 1

20

04/05/2001 17

Bad News Propagation: 2

A: 0 A: 3 A: 2 A: 3 A: 4 A: 51 1 1 1

20

8

04/05/2001 18

Black Hole

A

B

C

You

YourNeighbor

A: 3 hopsB: 2 hopsC: 2 hops

A: 1 hopB: 2 hops

04/05/2001 19

Black Hole Attack

R1

Destination N, NextHop R1, Metric 1

R2

R3

Rn

control flowdata flow

04/05/2001 20

BGP4• In between Link-State and Distance-Vector

– tell my neighbors about my connection to the rest of the world

– but, also tell them how I reach there:• routing path information.

– What can or can’t I do with the extra path information?

• Can I still attack?• How can I prevent or detect?

04/05/2001 21

Route Path (among AS’s)

A

B

C

A-B-E-F

E

F

A-C

04/05/2001 22

BGP Messages

• OPEN

• NOTIFICATION

• UPDATE (NEW and WITHDRAW)

04/05/2001 23

Internet BGP Update VolumeAnn and With at Mae-East

0

200,000

400,000

600,000

800,000

1,000,000

1,200,000

1,400,000

1,600,000

1,800,000

2,000,0004/17/1997

6/17/1997

8/17/1997

10/17/1997

12/17/1997

2/17/1998

4/17/1998

6/17/1998

8/17/1998

10/17/1998

12/17/1998

2/17/1999

4/17/1999

6/17/1999

8/17/1999

10/17/1999

12/17/1999

2/17/2000

Announcements

Withdraws

04/05/2001 24

Race Conditions and Paths

• T(shortest path) <= Tdown <= T(longest path)

B

A

04/05/2001 25

BGP Convergence ExampleR

AS0 AS1

AS2AS3

*B R via 3 B R via 03 B R via 23



AS0 AS1 AS2

** **B R via 203

*B R via 013 B R via 103

04/05/2001 26

ISP3-ISP4 Paths During Failure

ISP 3

Ste

ady

St a

t e

ISP 4

R3

P2

P2

ISP 5

FAULT

ISP 1

P3

P3

P6

P7

P7P4

P4

P5

P5

P5P5

P5

P6

P6

P6

ISP 7

ISP 9

ISP 8

P7

P7

P4

36% Average: 110 (min/max 78/135) seconds

Announce AS4 AS5 AS (52 seconds)

Withdraw (110 seconds)


Announce AS4 AS1 AS3 (39 seconds)



2% Average:140.00 (min/max 120/142)

Announce AS4 AS5 AS8 AS7 AS3 (27) Announce AS4 AS5AS9 AS8 AS7 AS3 (86)


27% Other

04/05/2001 27


Ste

ady

Sta

te

ISP 2

ISP 4

P2

P2

ISP 5

P3

P3

P3

ISP 6

R2

FAULT

Vagabond

P4

P4ISP 10

ISP 11

ISP 12

ISP 13

P4

P4

P4


AS4 AS5 AS2 (35 seconds)




Announce AS4 AS6 AS5 AS2 (61 seconds)




23% Other

04/05/2001 28


• Only one back up path (length 3)

Steady State

ISP 1

ISP 5

P2

P2ISP 4

R1

FAULT






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04/05/20011 ecs298k: Routing in General... lecture #2 Dr. S. Felix Wu Computer Science Department University of California, Davis wu