Routing II - Department of Computer Engineering

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Routing II

รศ.ดร. อนันต์ ผลเพิ่ม

Asso. Prof. Anan Phonphoem, [email protected]

http://www.cpe.ku.ac.th/~anan

Computer Engineering Department

Kasetsart University, Bangkok, Thailand

mailto:[email protected]

Outline

Intermediate-System to Intermediate-System (IS-IS)

Border Gateway Protocol (BGP)

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IS-IS


Integrated IS-IS (Support both TCP/IP and Connectionless Network Protocol: CLNP)

Link State routing protocol

Terminology

End systems (ES) Host

Intermediate System (IS) Router

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Timeline OSPF and IS-IS

4

many extensions for both protocols1998-2000

many ISPs switch from OSPF to IS-IS1996-1998

ISPs begin deployment of IS-IS (popular)1995

Large ISPs need an IGP; IS-IS is recommended1994

Most run OSPF (Very few deploy IS-IS)1992

Dual-mode IS-IS RFC published; OSPF v.2 RFC published1990-1991

OSPF v.1 RFC published

IS-IS becomes ISO proposed standard

1989

Originated by DEC phase V1985

IS-IS (from DEC) selected by ANSI as OSI intradomain protocol (CLNP only)

1987

OSPF work begins, loosely based on IS-IS1988

http://www.nanog.org

OSI: Two Network Services, Two Network Protocols

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OSI: Two Network Services, Two Network Protocols

CMNS (Connection Mode Network Service)

Requires establishment of a path @transport layer

CONP (Connection-Oriented Network Protocol)

CLNS (Connectionless Network Service)

Datagram support, No circuit establishment

CLNP (Connectionless Network Protocol)

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IS-IS Routers

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Level 1 IS (L1 IS, router) Analogous to OSPF Internal non-backbone router

(Totally Stubby)

Responsible for routing to End System (ES) inside an area.

Level 2 IS (L2 IS, router) Analogous to OSPF Internal Backbone router

Responsible for routing between areas

Level 1 and 2 IS (L1-L2 IS, router) Analogous to OSPF Area Border Router (ABR router)

Participate in both L1 intra-area routing and L2 inter-area routing.

OSPF Area

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ABR: Area Border RouterASBR: Autonomous System Border Router

IS-IS Area

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AS 23

L2 Area 0

AS 44

AS 193

L1 Area 3

L1 Area 2

L1 Area 1

L1/L2

L1/L2

L1/L2

L1/L2

Like ABR in OSPF

IS-IS Area

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Data Encapsulation & Addressing

IS-IS message are not carried in IP datagrams

Message called Protocol Data Units (PDU)

Encapsulated directly in Data Link Layer frames

SNPA (Subnetwork Point of Attachment)

Data Link Address

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IS-IS address format

Hierarchical Address

IDP: Initial Domain Part

DSP: Domain Specific Part

OSI network layer addressing is done through the NSAP (Network Service Access Point)

Represented in hexadecimal (up to 40 hex digits)

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NSAP

IS-IS address format

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Cisco format: Area – System ID – NSEL (always 00 on ISs)49.0001.2222.2222.2222.00

Variable Length Add.

NSAPs – Cisco Format

Area

Add. starting with 49 (AFI=49) are considered private IP add.

Routed by IS-IS

Should not be advertised to other CLNS networks (outside this IS-IS domain)

Additional 2 bytes (HODSP) added for the area ID

All routers in the same are must have the same area add.

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Area – System ID – NSEL 49.0001.2222.2222.2222.00

NSAP


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System ID

Same no. of bytes throughout the domain. Cisco fixes@ 6 bytes.

Customary can be

MAC address from the router

IP address of loopback interface

192.168.111.3 -> 192.168.111.003 -> 1921.6811.1003

Each device (IS and ES) must have a unique System ID within the area.


NSAP


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NSEL (NSAP Selector) NSEL is a service identifier like port or socket in TCP/IP. Not used in routing decisions. NSEL = 00 means the device itself (the network level

address) The NSAP with a NSEL = 00

is known as a Network Entity Title (NET)


NSAP

NSAP (NETs)

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Example: NSAP 39.0002.aaaa.bbbb.cccc.00Area ID is 39.0002System ID is aaaa.bbbb.cccc (4444.4444.4444)NSAP selector byte is 00

Network Representation

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In OSI, only two main types of physical links: Broadcast: usually LANs

Nonbroadcast: Point-to-Point, Multipoint, and dynamically established links (WAN links)

Thus, IS-IS supports only Broadcast (LAN) and Point-to-Point (for all other media)

Broadcast

Point-to-Point

Hello Message

To establish adjacencies with other routers (ISs) and ESs

Uses Hello PDUs.

3-type of Hello PDUs:

ESH, sent by ES to an IS

ISH, sent by IS to an ES

IIH, used between two ISs (normally transmitted every 10 seconds)

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Synchronization and Update Process

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LSP: Link State PDUPSNP: Partial Sequence Number PDU

If PSNP not received, resends LSP

IS-IS Routing Process

Divided into four stages:

Update process

Decision -- Uses Dijkstra’s algorithm to build a SPT (Shortest Path Tree)

Forwarding -- forwarding table

Receive

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Example: IP route @ SanJose1

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L1/L2

SanJose1#show ip route

Gateway of last resort is not set

i L2 192.168.30.0/24 [115/20] via 10.0.0.1, Serial0/0

C 192.168.10.0/24 is directly connected, FastEthernet0/1

172.16.0.0/24 is subnetted, 1 subnets

C 172.16.0.0 is directly connected, FastEthernet0/0

i L1 192.168.20.0/24 [115/20] via 172.16.0.2, FastEthernet0/0


C 10.0.0.0 is directly connected, Serial0/0

Example: IP route @ SanJose2

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L1/L2

SanJose2#show ip route

Gateway of last resort is 172.16.0.1 to network 0.0.0.0

i L1 192.168.10.0/24 [115/20] via 172.16.0.1, FastEthernet0/0


C 172.16.0.0 is directly connected, FastEthernet0/0



i L1 10.0.0.0 [115/20] via 172.16.0.1, FastEthernet0/0

i*L1 0.0.0.0/0 [115/10] via 172.16.0.1, FastEthernet0/0

Example: IP route @ Phoenix

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L1/L2

Phoenix#show ip route

Gateway of last resort is not set


i L2 192.168.10.0/24 [115/20] via 10.0.0.2, Serial0/0


i L2 172.16.0.0 [115/20] via 10.0.0.2, Serial0/0

i L2 192.168.20.0/24 [115/30] via 10.0.0.2, Serial0/0


C 10.0.0.0 is directly connected, Serial0/0

Outline



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Routing Protocol

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IGP (Interior Gateway Protocol) Exchange routing info. within an AS

RIP, IGRP, EIGRP, OSPF

EGP (Exterior Gateway Protocol) Exchange routing info. between AS

BGP

Autonomous System (AS) [RFC 1771] “A set of routers under the single technical

administration, using an IGP and common metrics to route packets within the AS, and using an EGP to route packets to other AS’s.”

Internet - Early Age

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EGP Restriction: •Tree only•One Backbone

อินเทอรเ์นต็แบ็คโบน

EGP

IGPAS 2

EGP

IGP AS 1

EGP

อินเทอรเ์นต็แบ็คโบน

EGPEGP

IGPAS 2

EGPEGP

IGP AS 1

EGPEGP

Internet Backbone

Internet – Current State

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BGP-4

ISP 1

IGP

BGP-4

BGP-4

BGP-4

BGP-4BGP-4

BGP-4 BGP-4BGP-4BGP-4

IGP

IGP

ISP 2 ISP 3

ISP Connection•Tree -> Graph

Autonomous System (AS)

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AS 1

AS 20

AS 5

AS 7

Autonomous System Boarder router (ASBR)

Exterior Gateway Protocol(EGP Link)

Interior Gateway Protocol(IGP Link)

This is the Internet !

BGP

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Border Gateway Protocol

BGP-4

Concentrate on Loop-Free > lowest cost

Based on policy

e.g. lowest # of AS

Need to go through AS 12

Advanced distance vector routing protocol Path Vector routing protocol

Path Vector Routing

Limitation of Distance vector / Link state

Interior routing protocol (Intra-Domain/AS)

Exterior routing protocol (Inter-Domain/AS)

Router holds

a list of networks that can be reached with the path (ASs to pass)

x.x.x.x can be reached through AS y

Analogy

National map (Distance Vector) road, city, distance

International Map (Path Vector) existing of cities in each country should be passed to reach destination

RFC 1772

Path Vector Routing Example

Path Vector Routing Example


Creating a BGP “peering” relationship involves an interesting combination of trust and mistrust

“Your ISP will show little patience with you if you make mistakes in your BGP configuration”.

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BGP Route Selection

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N4

AS 4

N5

AS 5

N6

AS 6

N7

AS 7

N2

AS 2

N3

AS 3

N1

AS 1

4.0.0.0

14.0.0.0

5.0.0.0

6.0.0.0

7.0.0.0

17.0.0.0

N2 ประกาศเส้นทาง(<4.0.0.0, 14.0.0.0, 5.0.0.0>,

<AS 2>) ให ้N1

N1 ประกาศเส้นทาง(<4.0.0.0, 14.0.0.0, 5.0.0.0>,

<AS1, AS 2>) ให้ N3

N4

AS 4

N5

AS 5

N6

AS 6

N7

AS 7

N2

AS 2

N3

AS 3

N1

AS 1

4.0.0.0

14.0.0.0

5.0.0.0

6.0.0.0

7.0.0.0

17.0.0.0

N2 ประกาศเส้นทาง(<4.0.0.0, 14.0.0.0, 5.0.0.0>,

<AS 2>) ให ้N1

N1 ประกาศเส้นทาง(<4.0.0.0, 14.0.0.0, 5.0.0.0>,

<AS1, AS 2>) ให้ N3

Route Announcement: no CIDR

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อินเทอร์เน็ต

202.0.1.0/24,202.0.32.0/24,

202.0.2.0/24,202.0.33.0/24,

202.0.3.0/24

202.0.0.0 -

202.0.255.0

ISP 3

ISP 1

202.0.32.0 -

202.0.47.0

202.0.0.0 -

202.0.15.0

202.0.2.0

202.0.3.0 202.0.32.0 202.0.33.0

202.0.1.0/24,

202.0.2.0/24,

202.0.3.0/24

202.0.32.0/24,

202.0.33.0/24ISP 2

202.0.1.0


202.0.1.0/24,202.0.32.0/24,

202.0.2.0/24,202.0.33.0/24,

202.0.3.0/24

202.0.0.0 -

202.0.255.0

ISP 3

ISP 1

202.0.32.0 -

202.0.47.0

202.0.0.0 -

202.0.15.0

202.0.2.0

202.0.3.0 202.0.32.0 202.0.33.0

202.0.1.0/24,

202.0.2.0/24,

202.0.3.0/24

202.0.32.0/24,

202.0.33.0/24ISP 2

202.0.1.0


202.0.1.0/24,202.0.32.0/24,

202.0.2.0/24,202.0.33.0/24,

202.0.3.0/24

202.0.0.0 -

202.0.255.0

ISP 3

ISP 1

202.0.32.0 -

202.0.47.0

202.0.0.0 -

202.0.15.0

202.0.2.0

202.0.3.0 202.0.32.0 202.0.33.0

202.0.1.0/24,

202.0.2.0/24,

202.0.3.0/24

202.0.32.0/24,

202.0.33.0/24ISP 2

202.0.1.0

Route Announcement: with CIDR

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202.0.1.0


202.0.0.0/16

202.0.0.0/16

ISP 3

ISP 1

202.0.32.0/20202.0.0.0/20

202.0.2.0

202.0.3.0 202.0.32.0 202.0.33.0

202.0.0.0/20 202.0.32.0/20

ISP 2

202.0.1.0


202.0.0.0/16

202.0.0.0/16

ISP 3

ISP 1

202.0.32.0/20202.0.0.0/20

202.0.2.0

202.0.3.0 202.0.32.0 202.0.33.0

202.0.0.0/20 202.0.32.0/20

ISP 2

202.0.1.0


202.0.0.0/16

202.0.0.0/16

ISP 3

ISP 1

202.0.32.0/20202.0.0.0/20

202.0.2.0

202.0.3.0 202.0.32.0 202.0.33.0

202.0.0.0/20 202.0.32.0/20

ISP 2

BGP Hazards -- Scenario

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Suppose, that through some misconfiguration you advertise 207.46.0.0/16 to your ISP.

Your ISP does not filter out and advertise to the Internet.

This CIDR block belongs to Microsoft, and you have just claimed to have a route to that destination.

Many decide that the best path to Microsoft is through your domain.

Flood of unwanted packets (black-holed traffic that should have gone to Microsoft)

They will be neither amused nor understanding.

By Rick Graziani

BGP Basics

BGP uses a list of AS numbers through which a packet must pass to reach a destination.

The function of BGP is to:

Exchange routing information between AS

Guarantee the selection of a loop free path.

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BGP Basics

BGP4

first version of BGP that supports CIDR and route aggregation.

Common IGPs such as RIP, OSPF, and EIGRP use technical metrics.

BGP does not use technical metrics.

Routing decisions based on

network policies, or rules

BGP does not show the details of topologies within each AS.

BGP sees only a tree of AS 40

BGP Basics

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BGP updates are carried using TCP on port 179.

In contrast, RIP updates use UDP port 520

OSPF, IGRP, EIGRP does not use a Layer 4 protocol

Because BGP requires TCP, IP connectivity must exist between BGP peers.

TCP connections must also be negotiated between them before updates can be exchanged.

Therefore, BGP inherits those reliable, connection-oriented properties from TCP.

Loop free Path

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AS Path: 10,20,30,40

AS 10

AS 20

AS 30 AS 40

AS Path: 10

AS Path: 10,20

AS Path: 10,20,30

AS Path: 10,20,30,40

BGP views the whole internetwork as a graph, or tree, of AS

BGP Operation

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When two routers establish a TCP-enabled BGP connection between each other, they are called neighbors or peers.

Each router running BGP is called a BGP speaker.

Exchange and Update

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Exchange Incremental updates

Withdraw route

Peers exchange keepalive messages (e.g. 60 sec for Cisco)

to ensure the connection is maintained.

BGP Message

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There are four BGP message types:

Type 1: OPEN (After the TCP establishment, both neighbors send Open messages)

Type 2: KEEPALIVE

Type 3: UPDATE

Type 4: NOTIFICATION

All BGP messages are Unicast to the one neighbor over the TCP connection.

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Thaisarn Uninet

Internet

OCS

LIB ENG

KU Gateway

50Year

SCI

Firewall & Shaper & Cache

KPS

SRI

CSC

RAT

NOP

SATITOCS

SPN

1G

1G

1G

1G

34M

34M

2M

100M

2M

6M

24 April 2005

2M

Area 1

Area 2

Area 3

Area 5

Area 4

Area 10

Area 11

Area 12

Area 13

Area 0

512K

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48

49

50

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National – Feb 2010

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International - Feb 2010

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References

CCNP slide by Rick Graziani, Cabrillo College, Feb. 2004

Internet Information Research Center (IIRC)

http://iir.ngi.nectec.or.th

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Routing II - Department of Computer Engineering

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