CS 145ACS 145ACase Study: Case Study:

Simplified BGP Simplified BGP Finite State Finite State

MachineMachineNetlab.caltech.edu/courseNetlab.caltech.edu/course

TodayToday Brief Introduction of routing Brief Introduction of routing

protocolsprotocols An example of Finite State MachineAn example of Finite State Machine Lab 3Lab 3

What does the Internet What does the Internet look like?look like?

Example: (/sbin/traceroute) Example: (/sbin/traceroute) C:\>tracert cwis.usc.eduC:\>tracert cwis.usc.eduTracing route to cwis.usc.edu [128.125.253.146]Tracing route to cwis.usc.edu [128.125.253.146]1 <1 ms Jorgensen-RSM-44.caltech.edu [131.215.44.253]1 <1 ms Jorgensen-RSM-44.caltech.edu [131.215.44.253]2 <1 ms Booth-border.ilan.caltech.edu [131.215.254.254]2 <1 ms Booth-border.ilan.caltech.edu [131.215.254.254]3 <1 ms CalREN-Caltech.caltech.edu [192.41.208.49]3 <1 ms CalREN-Caltech.caltech.edu [192.41.208.49]4 <1 ms JPL--CIT.POS.calren2.net [198.32.248.5]4 <1 ms JPL--CIT.POS.calren2.net [198.32.248.5]5 1 ms UCLA--JPL.POS.calren2.net [198.32.248.1]5 1 ms UCLA--JPL.POS.calren2.net [198.32.248.1]6 1 ms ISI--UCLA.POS.calren2.net [198.32.248.29]6 1 ms ISI--UCLA.POS.calren2.net [198.32.248.29]7 2 ms USC--ISI.POS.calren2.net [198.32.248.25]7 2 ms USC--ISI.POS.calren2.net [198.32.248.25]8 3 ms rtr43-c2-gw.usc.edu [128.125.251.66]8 3 ms rtr43-c2-gw.usc.edu [128.125.251.66]9 2 ms rtr-gw-1.usc.edu [128.125.254.1]9 2 ms rtr-gw-1.usc.edu [128.125.254.1]10 2 ms cwis.usc.edu [128.125.253.146]10 2 ms cwis.usc.edu [128.125.253.146]

Topology of the NetworkTopology of the Network131.215.44.214

131.215.44.253

131.215.254.254

192.41.

208.49

198.32.

248.5198.32.

248.1198.32.

248.29

198.32.

248.25

128.125.251.66

128.125.253.146

128.125.254.1

The Journey of a packet (1)The Journey of a packet (1)131.215.44.214-131.215.44.214->131.215.44.253>131.215.44.253

131.215.44.214

131.215.44.253 131.215.

254.254

192.41.

208.49

198.32.

248.5198.32.

248.1198.32.

248.29

198.32.

248.25

128.125.251.66

128.125.253.146

128.125.254.1

The Journey of a packet (2)The Journey of a packet (2)131.215.44.253131.215.44.253

IPIP

MACMAC

PhysicPhysic Get a packet From EthernetGet a packet From EthernetIt’s for 00:90:6D:E7:D4:00. It’s for 00:90:6D:E7:D4:00.

That’s me. I should accept it.That’s me. I should accept it.

131.215.44.214

131.215.44.253

131.215.254.254

The Journey of a packet (2)The Journey of a packet (2)131.215.44.253131.215.44.253

IPIP

MACMAC ““OK, I am 00:90:6D:E7:D4:00”OK, I am 00:90:6D:E7:D4:00”Pass the packet to IPPass the packet to IP

PhysicPhysic Get a packet from ethernet for : 00:Get a packet from ethernet for : 00:90:6D:E7:D4:0090:6D:E7:D4:00

131.215.44.214

131.215.44.253

131.215.254.254

The Journey of a packet (2)The Journey of a packet (2)131.215.44.253131.215.44.253

IPIP [IP] Header: [IP] Header: From 131.215.44.214 to From 131.215.44.214 to

“128.125.253.146”“128.125.253.146”““Should go to next router: Should go to next router:

131.215.254.254”131.215.254.254”MACMAC ““OK, I am 00:90:6D:E7:D4:00”OK, I am 00:90:6D:E7:D4:00”

Pass the packet to IPPass the packet to IPPhysicPhysic Get a packet from ethernet for: 00:Get a packet from ethernet for: 00:90:6D:E7:D4:0090:6D:E7:D4:00

131.215.44.214

131.215.44.253

131.215.254.254

Necessary Information Necessary Information (1)(1)

Where shall I pass the packet, for a given Where shall I pass the packet, for a given destination IP address? – Routing Tabledestination IP address? – Routing Table Exmaple:Exmaple:[weixl@orchestra:~]> route[weixl@orchestra:~]> route

DestinatiDestinationon

GatewayGateway Gen-maskGen-mask FlaFlagsgs

InterfaInterfacece

131.215.131.215.44.044.0

** 255.255.2255.255.255.055.0

UU Eth0Eth0

127.0.0.0 127.0.0.0 ** 255.0.0.0255.0.0.0 UU lolodefault default 131.215.44131.215.44

.254.2540.0.0.00.0.0.0 UFUF Eth0Eth0

How can the How can the routers know the routers know the

routing routing information?information?

How?How? Manually add/delete routing entriesManually add/delete routing entries Automatically exchange routing Automatically exchange routing

information between routers.information between routers.

Routing ProtocolRouting ProtocolA: hi, are you there?A: hi, are you there?B: yes.B: yes.A: Can I tell you a piece of news?A: Can I tell you a piece of news?B: Sure.B: Sure.A: I have a way to get to www.usc.edu.A: I have a way to get to www.usc.edu.B: ok. I will send you all the packets that are going to wB: ok. I will send you all the packets that are going to www.usc.edu. ww.usc.edu. ……B: Hi, Can I tell you some news, too?B: Hi, Can I tell you some news, too?A: Yes!A: Yes!B: I can connect to all the machines in “cs.caltech.edB: I can connect to all the machines in “cs.caltech.edu”u”A: ok. I will send you all the packets that are going to A: ok. I will send you all the packets that are going to “cs.caltech.edu”.“cs.caltech.edu”.…………

131. 215.44. 253

(B)

131. 215.254. 254

(A)

Routing ProtocolRouting ProtocolA to C: hi, are you there?A to C: hi, are you there?......A to C: hi, are you there?A to C: hi, are you there?……A to B: I think C is down. And from A to B: I think C is down. And from

now on, I cannot contact USC.now on, I cannot contact USC.B: OK. I will try other paths when I B: OK. I will try other paths when I

get packets for USC.get packets for USC.……

131. 215.44. 253

(B)

131. 215.254. 254

(A)

192. 41.208. 49

(C)

Routing ProtocolRouting Protocol Good: Efficiently broadcast up-to-Good: Efficiently broadcast up-to-

date routing informationdate routing information Bad: Rumor may be broadcast Bad: Rumor may be broadcast

efficiently, too.efficiently, too. Argument: If the majority is good…Argument: If the majority is good… The algorithm should be correct in The algorithm should be correct in

distributed environments.distributed environments.

Routing ProtocolsRouting Protocols Autonomous SystemAutonomous System

Routing ProtocolsRouting Protocols Inside Autonomous System: Inside Autonomous System:

Embrace the Freedom!Embrace the Freedom!• RIP (Routing Information Protocol)RIP (Routing Information Protocol)• OSPF (Open Shortest Path First)OSPF (Open Shortest Path First) Between Autonomous System Between Autonomous System

(Exterior Gateway Protocol): More (Exterior Gateway Protocol): More consideration…consideration…

• BGP (Border Gateway Protocol)BGP (Border Gateway Protocol)

Border Gateway Border Gateway Protocol-4Protocol-4

Inter-Autonomous System Inter-Autonomous System CommunicationCommunication

Propagate Path InformationPropagate Path Information Support PolicySupport Policy Incremental UpdatesIncremental Updates Assume reliable transmission (TCP)Assume reliable transmission (TCP) http://www.ietf.org/rfc/rfc1771.txthttp://www.ietf.org/rfc/rfc1771.txt

Simplified BGP State Simplified BGP State MachineMachineEvent/ Acti on Li st

1 Request for Connecti on2 Connecti on Succeeded3 Connecti on Fai l ed4 "Open" Recei ved5 "KeepAl i ve" Recei ved6 "Update" Recei ved7 "Noti fi cati on" Recei ved8 "Open" Sent9 "KeepAl i ve" Sent10 "Update" Sent11 "Noti fi cati on" Sent12 Cl ose connecti on13 Any Error, i ncl udi ng:TCP operat i on error,Packets f ormat error,Packets type error.

14 KeepAl i ve Ti mer Expi re15 KeepAl i ve Ti mer Reset16 Hol dOn Ti mer Reset17 Hol dOn Ti mer Expi re

-/10

Idle

Active OpenSent

OpenConfirmed

EstablishedConnect

-/81/-

4/9

5/- (15,16)3/12

2/-4/8, 9

6/-Any StateOther thanIdle/Active/

Connect IdleEstablished

BGP PacketsBGP Packets Packets Format:Packets Format:

00－－ 1515thth Byte: FF (hexadecimal) Byte: FF (hexadecimal) 16-1716-17thth Byte: Unsigned number, Length of Byte: Unsigned number, Length of the Packet (>=19)the Packet (>=19) 1818thth Byte: Packet Type: Byte: Packet Type:

11 OPENOPEN 22 UPDATEUPDATE 33 NOTIFICATIONNOTIFICATION 44 KEEPALIVEKEEPALIVE

1919thth Byte to the end of the Packet: Routing Data Byte to the end of the Packet: Routing Data

Detailed SpecificationDetailed Specification http://www.ietf.org/rfc/rfc1771.txthttp://www.ietf.org/rfc/rfc1771.txt

Appendix I (page 47)Appendix I (page 47)

Lab 3Lab 3

Lab 3 - TaskLab 3 - Task Implement a (simplified) simplified Implement a (simplified) simplified

BGP Finite State Machine:BGP Finite State Machine:• Ignore the timersIgnore the timers• Ignore the details of Routing DataIgnore the details of Routing Data

Lab3 - Finite State Lab3 - Finite State MachineMachine

Event/ Acti on Li st1 Request for Connecti on2 Connecti on Succeeded3 Connecti on Fai l ed4 "Open" Recei ved5 "KeepAl i ve" Recei ved6 "Update" Recei ved7 "Noti fi cati on" Recei ved8 "Open" Sent9 "KeepAl i ve" Sent10 "Update" Sent11 "Noti fi cati on" Sent12 Cl ose connecti on13 Any Error, i ncl udi ng:TCP operat i on error,Packets f ormat error,Packets type error.

-/10

Idle

Active OpenSent

OpenConfirmed

EstablishedConnect

-/81/-

4/9

5/-3/12

2/-4/8, 9

6/-Any StateOther thanIdle/Active/

Connect Idle

Lab 3 - RequirementsLab 3 - Requirements The implementation is based on TCP.The implementation is based on TCP. The implementation is able to actively The implementation is able to actively

connect to multiple machines and it is able connect to multiple machines and it is able to accept requests from multiple machines.to accept requests from multiple machines.

The implementation allows at most one The implementation allows at most one connection from one machine (identified by connection from one machine (identified by IP / hostname).IP / hostname).

For each connection, the implementation For each connection, the implementation implements the Lab3 Finite State Machine.implements the Lab3 Finite State Machine.

Lab 3 - DetailsLab 3 - Details A program “server” A program “server” Read from a file called “server.conf”. Format Read from a file called “server.conf”. Format of “server.conf”:of “server.conf”:• (1(1stst line:) Listen_Port Connection_Num(N) line:) Listen_Port Connection_Num(N)• (2(2ndnd line:) IP_1 Port_1 line:) IP_1 Port_1• (…)(…)• (N+1(N+1stst line:) IP_N Port_N line:) IP_N Port_N The server should read from “server.conf”, liThe server should read from “server.conf”, listen to Listen_Port for new connection, at the ssten to Listen_Port for new connection, at the same time, actively connect the specified machiame time, actively connect the specified machines (IP_1:Port_1, IP_2:Port_2, … IP_N:Port_N)nes (IP_1:Port_1, IP_2:Port_2, … IP_N:Port_N)

Lab 3 - Possible Lab 3 - Possible ProblemsProblems

Implementation of Finite State Implementation of Finite State MachineMachine

Check the errors (including Check the errors (including operation errors and Packet errors)operation errors and Packet errors)

Multiple connections from the same Multiple connections from the same machinemachine

Lab 3 - TipsLab 3 - Tips Re-Use the codes in Lab 1Re-Use the codes in Lab 1 How to implement the Finite State How to implement the Finite State

Machine?Machine?• ““if … then…”if … then…”• ““State transition table”State transition table” How to test?How to test? Incremental DevelopmentIncremental Development DON’T START AT THE LAST MOMENT!DON’T START AT THE LAST MOMENT!

Lab 3 Lab 3 Due: Dec 1Due: Dec 1stst (Sunday) 23:59:59 (Sunday) 23:59:59 Email: Email: weixl@caltech.eduweixl@caltech.edu GradingGrading TA hours: TA hours: Tue / Thu (20:00 – 22:00) JRG 170Tue / Thu (20:00 – 22:00) JRG 170ExceptExcept: Nov.19 / Nov.21: Nov.19 / Nov.21