ilab Lab 1+2 The Basics / Static Routing ISO/OSI Layer Model - - PowerPoint PPT Presentation

Lehrstuhl für Netzarchitekturen und Netzdienste

Institut für Informatik Technische Universität München

ilab

Lab 1+2 The Basics / Static Routing

Ilab: The basics / Static Routing 2

ISO/OSI Layer Model (1979-1983)

Application Layer Presentation Layer Session Layer Transport Layer

4 5 6 7

Network Layer Data Link Layer Physical Layer

1 2 3

Applications, e.g. HTTP, FTP, … Management of Sessions Representation of data Transport, e.g. TCP, UDP, SCTP Routing, e.g. IP Transmission of frames Physical layer, e.g. Ethernet

Ilab: The basics / Static Routing 3

Internet Layer Model vs. ISO/OSI

Application Layer Transport Layer Internet Layer Link Layer Interface to the physical medium

Ethernet, WLAN, Token Ring, FDDI, …

Routing in the internet

IPv4, IPv6

End-to-end data transport

tcp, udp, sctp, …

Applications

http, ftp, telnet, smtp, pop, …

• Alternative name: TCP/IP protocol hierarchy
• Adaptation of the abstract ISO/OSI layer model for the internet
• ISO/OSI layers 5, 6, 7 and layers 1, 2 are aggregated

1 2 3 4

3 1 2 4 6 x 5 = Equivalent to ISO/OSI 7

Ilab: The basics / Static Routing 4

Horizontal Communication

Router Router

Telephone, modem SDH / SONET (Hi-Speed Fibre) WLAN

Application TCP IP Net 1 IP Net 1 Net 2 IP Net 2 Net 3 Application TCP IP Net 3

1 2 3

• Horizontal communication = logical communication between

instances of the same protocol layer over an abstract medium

• Only the lowest layer has a real (indirect) connection with the partner

instance

4

Ilab: The basics / Static Routing 5

Vertical Communication

Router Router

Telefone, Modem SDH / SONET (Hi-Speed Fiber) WLAN

Application TCP IP Net 1 IP Net 1 IP Application TCP IP Net 2 Net 2 Net 3 Net 3

1 2 3

• Vertical communication = Instances of a protocol layer

communicate with instances of protocol layers above or below.

4

Ilab: The basics / Static Routing 6

Cooperation of Protocol Instances: PDUs

 A service provides a Service Access Point (SAP) to the layer above it  Protocol Data Units (PDUs) are encapsulated  TCP/UDP adds process addressing (ports) to IP

• TCP adds reliability to IP

 IP routes data packets through the network to the destination

MAC/LLC-Header IP-Header TCP/UDP-Header IP-Header TCP/UDP-Header UDP-Header Data Application Transport Layer Link Layer Internet Layer TCP-Header

bzw.

Data Data Data Data Trailer

1 2 3 4

Ilab: The basics / Static Routing 7

Internet Architecture: Common Design Decisions

 Hold no information (state) in nodes between sender of data and

destination (e.g. no need for resynchronisation)

 All information specific for the stream is stored only at the sender and

the destination of data: End-to-end principle

 Separation of packet forwarding from one hop to the next and the

creation of routing tables

• Routing vs. Forwarding

Ilab: The basics / Static Routing 8

TCP/IP Protocol Family – Overview

• „TCP/IP“is used often as a synonym for a whole family of protocols
• The TCP/IP family and the ISO/OSI layer model:
• ICMP and IGMP use IP like an application layer (ISO/OSI) protocol, but

are assigned to the network layer (ISO/OSI)

• Application layer (ISO/OSI) protocols are e.g. FTP, TELNET or SMTP

ICMP RARP ARP TCP UDP IP

Session Layer

Transport Layer Network Layer Data Link Layer

IGMP

Ilab: The basics / Static Routing 9

Properties of IP

 Paket-switched  Connectionless datagram service  Unreliable transmission:

• Datagramms may get lost
• Datagramms may overtake each other
• Datagramms may be forwarded ad infinitum (routing loop)
• Transmission errors that could not be fixed by the layer 2 protocol used,

normally cannot be fixed by IP, too

 ICMP (Internet Control Message Protocol) is used for error notification  No flow control  Used in private and public networks

• Private home networks
• Coupling of subnetworks in enterprise networks
• Public (wide area) networks (e.g. in the internet backbone)

 Best effort, no quality of service (QoS) guaranteed

Ilab: The basics / Static Routing 10

Version Hdr.Len DiffServ Total Length Identifier Flags Fragment Offset Protocol Time to Live Header Checksum Source Address Destination Address Options and Padding Data 3 7 15 31 IP-Header

0 DF MF

Reserved Don‘t Fragment More Fragments Bit

DiffServ Codepoint ECN

Congestion Control (Explicit Congestion Notification) QoS Class

IPv4 Datagramm Layout

Ilab: The basics / Static Routing 11

Control of IP: ICMP

 IP only provides (unreliable) paket transmission  When errors occur or for testing purposes ICMP (Internet Control

Message Protocol) is used.

 ICMP uses IP  Message type, examples:

• Echo Request / Reply: Echo Reply is requested ("ping").
• Timestamp Request / Reply: similar to Echo Request: a timestamp that

holds the time of arrival (query) and time of sending (response) is added. Router connection interrupted Router Router ICMP message Sender Destination Router

Ilab: The basics / Static Routing 12

ICMP: Error messages

 Destination unreachable:

A data packet could not be delivered, e.g. because of an interrupted cable or a router failure.

 Time to live exceeded:

A data packet was dropped by a router because the packet‘s TTL exceeded.

 Parameter problem:

A data packet was discarded due to illegal values in its IP header.

 Source quench:

A overloaded communication system requests the sender to throttle transmission rate.

 Redirect:

A data packet should be sent over another router.

Ilab: The basics / Static Routing 13

Type Code Checksum

ICMP: Packet layout

 Transmission of ICMP messages

• ICMP messages are transmitted in

IP-packets.

• ICMP messages have the value „1“

in the protocol field of the IP header.

 Format of ICMP messages

• Type: the type of this message, e.g. Type = 3 means „Destination

unreachable“)

• Code: more specific information, e.g. „Network not reachable“)
• Checksum: Checksum over the ICMP message
• The content of the Info-Field depends on the Type of the ICMP message,

e.g. timestamps

IP Header [Protocol = 1] ICMP Message Info

Ilab: The basics / Static Routing 14

 MAC addresses (also referred to as “physical address”)

• Specific for the network type, e.g. Ethernet, Bluetooth, ATM
• Are not unique for all network types

 Ethernet / WLAN 48 Bit long (z.B.: aa:bb:cc:dd:ee:ff )  Contains information about vendor and product  MAC addresses are not hierarchically issued, e.g.:

• Device with MAC aa:bb:cc:dd:ee:ff is located in the US
• Device with MAC aa:bb:cc:dd:ee:fe is located in Japan

 When MAC addresses would be used for global addressing of devices, routing of packets would not scale as every router would need to know the route to every possible destination

Layer 2 Adresses

Ilab: The basics / Static Routing 15

Routing Inside the Internet

 IP addresses are 32 bit long  this results in 2^32 possible host

addresses

 A naive approach would result in huge routing tables, a router would

need to know all routes to all end systems  impossible

 Better approach: Hierarchical Addressing

• Use first n bit of the IP address for addressing the network
• Use last 32 - n bit of the IP address for addressing the host inside the

network

 Effect:

• A router only needs to know how to reach the hosts within the own network
• For reaching hosts outside the own network, the router only needs to know

the router that „cares“ for the destination network

Ilab: The basics / Static Routing 16

0 1 2 4 8 16 24 31 1 Net-ID Net-ID 1 1 Net-ID Node-ID Node-ID Node-ID 1 1 1 1 Reserved for future use

IP Address Classes

• 1. Class A: Nets with up to 16 million nodes (prefix: 1 bit/ net: 7 / host: 24)
• 2. Class B: Nets with up to 65.536 nodes (2/ 14/ 16)
• 3. Class C: Nets with up to 256 nodes (3/ 21/ 8)
• 4. Class D: used for group communication (multicast)
• 5. Class E, unused, reserved for future use

1 1 1 Multicast Address

Ilab: The basics / Static Routing 17

Subnetworks

 Purpose: Split the static Class A, B C networks into parts (subnets)  Use:

• Makes large (Class A) networks manageable
• Easier network administration
• Separation of business units
• …

 Implemented with subnetwork masks

• Bsp: 255.255.255.0

Ilab: The basics / Static Routing 18

IP Subnetwork Addresses

 IP-Address (in this example: Class B , prefix 10, 2/14/16):

 Subnetwork mask marks the bits that describe the network and the

• subnetwork. In the binary representation of the subnetwork mask this area is

represented with a sequence of set bits („1“)

• Example:

IP-Addresse: 129. 13.

• 3. 64

Subnetmask: 255.

• 255. 255. 0

1111 1111 1111 1111 1111 1111 0000 0000 Network: 129. 13. Subnetwork: 3. Endsystem: 64

• The network part can be derived from the address class.
• If the subnetwork mask only covers the network part (e.g. 255.255.0.0), no

subnetwork is specified. Network Part Network Part Local Part Subnet Part Host Part

Ilab: The basics / Static Routing 20

CIDR: Classless Inter-Domain Routing

 Diadvantage of fixed address classes:

• Up to now: three address classes with fixed length prefixes for unicast.
• Bad utilization of IP address space due to unused addresses.

 Example:

• A company needs 1000 IP addresses and requests a Class B network
• A Class B network contains more than 65000 addresses. This means,
• ver 64000 addresses are not in use!

 CIDR: Replace fixed network classes with network prefixes of

arbitrary length:

• E.g.: 129.24.12.0/14: The first 14 Bits are used for network identification
• Used in combination with hierarchical routing:
• Backbone-Router, e.g. a Transatlantic Link, only needs to pay attention to the

first 13 Bits  smaller routing tables, smaller costs

• Router of a ISP pays attention to first 15 Bit
• Router in a (small) company network pays attention to first 25 Bits

Ilab: The basics / Static Routing 22

ARP - Introduction

 ARP = Address Resolution Protocol  Purpose:

• When IP needs to send out a packet, it needs to know the MAC address of

the next hop

• ARP resolves the MAC address of a given IP address
• IP packet then is encapsulated in a Link Layer frame and sent to the next

hop

 ARP cache: a system remembers MAC addresses of recently resolved

IP addresses

• Increases performance

Ilab: The basics / Static Routing 23

ARP - Example Setup

Source IP 202.34.5.27 MAC ..:f7:a1 Host 1 IP 202.34.5.11 MAC ..:e0:10 Destination IP 84.6.7.8 MAC 7 Host 2 IP 84.6.7.10 MAC 5 Router IP 202.34.5.2 MAC ..:b1:f2 IP 84.6.7.254 MAC 2

 Example setup:

• 2 networks are connected via a router
• Router translates from Ethernet to some other physical medium
• All ARP caches are empty  nobody knows any MAC address
• All routing tables are correct

 Now the sender wants to send a packet to the destination …

Ethernet Some network with 8 bit long MAC addresses

Ilab: The basics / Static Routing 24

ARP vs. Routing

 Source wants to send a packet to 84.6.7.8 (destination)  The destination is not located in the own network

 The sender determines the next hop which is the router (default gateway)  Result: the next layer 3 hop is the router with the IP 202.34.5.2

 The semder first needs to resolve the MAC address of the router

Source IP 202.34.5.27 MAC ..:f7:a1 Host 1 IP 202.34.5.11 MAC ..:e0:10 Destination IP 84.6.7.8 MAC 7 Host 2 IP 84.6.7.10 MAC 5 Router IP 202.34.5.2 MAC ..:b1:f2 IP 84.6.7.254 MAC 2

Ilab: The basics / Static Routing 25

ARP – Request 1

Source IP 202.34.5.27 MAC ..:f7:a1 Host 1 IP 202.34.5.11 MAC ..:e0:10 Destination IP 84.6.7.8 MAC 7 Host 2 IP 84.6.7.10 MAC 5 Router IP 202.34.5.2 MAC ..:b1:f2 IP 84.6.7.254 MAC 2

Ethernet Frame: DST: Broadcast (..:ff:ff) SRC: ..:f7:a1 Type: ARP Address Resolution Protocol (Request) Hardware Type: Ethernet Protocol Type: IP Hardware Size: 6 Protocol Size: 4 Sender MAC: ..:f7:a1 Sender IP: 202.34.5.27 Target MAC: ..:00:00 Target IP: 202.34.5.2

Ilab: The basics / Static Routing 26

ARP – Reply 1

Source IP 202.34.5.27 MAC ..:f7:a1 Host 1 IP 202.34.5.11 MAC ..:e0:10 Destination IP 84.6.7.8 MAC 7 Host 2 IP 84.6.7.10 MAC 5 Router IP 202.34.5.2 MAC ..:b1:f2 IP 84.6.7.254 MAC 2

Ethernet Frame: DST: ..:f7:a1 SRC: ..:b1:f2 Type: ARP Address Resolution Protocol (Reply) Hardware Type: Ethernet Protocol Type: IP Hardware Size: 6 Protocol Size: 4 Sender MAC: ..:b1:f2 Sender IP: 202.34.5.2 Target MAC: ..:f7:a1 Target IP: 202.34.5.27

This node will not interfere

Ilab: The basics / Static Routing 27

Forwarding

Source IP 202.34.5.27 MAC ..:f7:a1 Host 1 IP 202.34.5.11 MAC ..:e0:10 Destination IP 84.6.7.8 MAC 7 Host 2 IP 84.6.7.10 MAC 5 Router IP 202.34.5.2 MAC ..:b1:f2 IP 84.6.7.254 MAC 2

Ethernet Frame: DST: ..:b1:f2 SRC: ..:f7:a1 Type: IP Internet Protocol: Source: 202.34. 5.27 Destination: 84. 6. 7. 8 … Payload, Payload, Payload, Payload, Payload, Payload, Payload, Payload, Payload, Payload, Payload, Payload,



The IP packet is forwarded from sender to the router

MAC address

• f next hop

Final destination

Ilab: The basics / Static Routing 28

Forwarding

Source IP 202.34.5.27 MAC ..:f7:a1 Host 1 IP 202.34.5.11 MAC ..:e0:10 Destination IP 84.6.7.8 MAC 7 Host 2 IP 84.6.7.10 MAC 5 Router IP 202.34.5.2 MAC ..:b1:f2 IP 84.6.7.254 MAC 2

 The router recognizes, that the destination is directly reachable by him  The router now needs the layer 2 address of the destination

Ilab: The basics / Static Routing 29

ARP – Request 2

Source IP 202.34.5.27 MAC ..:f7:a1 Host 1 IP 202.34.5.11 MAC ..:e0:10 Destination IP 84.6.7.8 MAC 7 Host 2 IP 84.6.7.10 MAC 5 Router IP 202.34.5.2 MAC ..:b1:f2 IP 84.6.7.254 MAC 2

L2 Frame: DST: Broadcast (ff) SRC: 2 Type: ARP Address Resolution Protocol (Request) Hardware Type: XY Protocol Type: IP Hardware Size: 1 Protocol Size: 4 Sender MAC: 2 Sender IP: 84.6.7.254 Target MAC: 0 Target IP: 84.6.7.8 In this network, MAC addresses are 1 bit long!

Ilab: The basics / Static Routing 30

ARP – Reply 2

Source IP 202.34.5.27 MAC ..:f7:a1 Host 1 IP 202.34.5.11 MAC ..:e0:10 Destination IP 84.6.7.8 MAC 7 Host 2 IP 84.6.7.10 MAC 5 Router IP 202.34.5.2 MAC ..:b1:f2 IP 84.6.7.254 MAC 2

L2 Frame: DST: 2 SRC: 7 Type: ARP Address Resolution Protocol (Reply) Hardware Type: XY Protocol Type: IP Hardware Size: 1 Protocol Size: 4 Sender MAC: 7 Sender IP: 84.6.7.8 Target MAC: 2 Target IP: 84.6.7.254

Ilab: The basics / Static Routing 31

All done!

 The router obtained the needed information for delivering the packet

Source IP 202.34.5.27 MAC ..:f7:a1 Host 1 IP 202.34.5.11 MAC ..:e0:10 Destination IP 84.6.7.8 MAC 7 Host 2 IP 84.6.7.10 MAC 5 Router IP 202.34.5.2 MAC ..:b1:f2 IP 84.6.7.254 MAC 2

XY MAC Frame: DST: 7 SRC: 2 Type: IP Internet Protocol: Source: 202.34. 5.27 Destination: 84. 6. 7. 8 … Payload, Payload, Payload, Payload, Payload, Payload, Payload, Payload, Payload, Payload, Payload, Payload, Mac address

• f next hop

Final destination

Ilab: The basics / Static Routing 32

Wireshark

 aka „Ethereal“  Powerful tool that ...

• captures all packets sent by a machine,
• parses the packets,
• and displys them in a neat list.

 Very useful for debugging protocols...  ... and for understanding them  Networker‘s best friend 

Ilab: The basics / Static Routing 33

ARP - Query MAC broadcast inside the local subnet

Ilab: The basics / Static Routing 34

ARP - Reply

Do not get confused. The IP addresses printed here are added as a service from

• wireshark. Inside the real

packet, they do not exist here.

Lehrstuhl für Netzarchitekturen und Netzdienste

Institut für Informatik Technische Universität München

ilab

Lab 3 Dynamic Routing

2 ilab: Dynamic Routing

Recap: Static Routing

Ciscorouter, IPv4, ICMP, ARP

Session Presentation Application Physical Datalink Network Transport Network Transport Application Host-to-Net TCP/ IP ISO/ OSI

Concepts, Hardware, Software

• 1. Setup - static routing
• 2. The routing table
• 3. The default gateway
• 4. Packet forwarding
• 5. Further configuring of the Cisco router
• 6. Checking if everything is set up correctly
• 7. Watching the packets travel
• 8. One more interesting experiment...
• 9. Suggestions/ complaints
• 10. Please remove the Cables

Minicom

3 ilab: Dynamic Routing

Dynamic Routing

RIP, OSPF, BGP Session Presentation Application Physical Datalink Network Transport Network Transport Application Host-to-Net TCP/ IP ISO/ OSI

Concepts, Hardware, Software

• 1. Setup - Dynamic routing
• 2. RIP (Cisco/ Linux)

2.4. What did RIP do? 2.5. Changing the setup a little... 2.6. Configuring the serial link 2.7. RIP done.

• 3. OSPF (without/ with areas)

3.3. Distance values 3.6. Compare: OSPF with and without areas 3.7. Ad-/ Disadvantages of OSPF area routing 3.8. Inspecting OSPF packets

• 4. BGP

4.1. Autonomous systems Cisco Serial Link

Zebra

4 ilab: Dynamic Routing

Routing – Problem definition



Given: Graph



Main problem:

• How to determine the shortest

path tree in order to forward packets to their destination



Subproblems:

• 1. Information gathering - which information do we need
• 2. Path calculation
• 3. Forwarding – how does a node decide?
• Based on its routing table

Routing algorithms solve subproblems 1 and 2

A E D C B F

2 2 1 3 1 1 2 5 3 5

5 ilab: Dynamic Routing

Distance Vector Routing

Approach



Information gathering

• Neighboring nodes share their

routing information (destination, costs)

• Distributed (only with neighbors)



Path calculation

• Distance table is updated if routing information

has changed

• e.g. costs have changed



Outcome

• Update routing table if the best (least expensive) entry in distance table has

changed

A E D C B F

2 2 1 3 1 1 2 5 3 5

B costs 2 C costs 4 D costs 1 E costs 2 F costs 4 A costs 1 B costs 2 C costs 3 E costs 1 F costs 3

?

6 ilab: Dynamic Routing

Distance Table

D () A B C D A 1 7 6 4 B 15 8 9 11 D 5 5 4 2

E

Costs to destination via

7 8 1 2 1 2

A B C D E

D (Y,Z)

X Distance from X to Y via Z c(X,Z) + min {D (Y,w)}

Z

= =

D (C,D)

E

c(E,D) + min {D (C,w)}

D w

=

= 2+2 = 4

Loop!



Example



Distance table contains unwanted routes

• Loops result in endlessly circulating packets (until the TTL field expires)

D (C,A)

E

c(E,A) + min {D (C,w)}

A w

=

= 1+5 = 6

7 ilab: Dynamic Routing

Distance table -> Routing table D () A B C D A 1 7 6 4 B 15 8 9 11 D 5 5 4 2

E costs via

A B C D A,1 D,5 D,4 D,2

Exit link, costs

Distance table

• f E

Routing table

• f E

8 ilab: Dynamic Routing

Changes of the topology and of costs

Rule:

 good news travels fast  bad news travels slowly - “count to infinity” problem!

Y: direct link to X changed -> Use route via Z (loop) Y: Propagates new route to X Z: Updates costs to X via Y

X

1 4 50 60

etc.

Y Z

9 ilab: Dynamic Routing

Split Horizon with poison reverse, path vector

 Situation

• Link D-E fails
• A told D that it can reach E in 2 hops
• D takes new Route via A (D-A-D-E)

 Split-Horizon

• Update messages of node A to D do not contain routes to nodes, which A

would route via D

 Poison Reverse

• Cost entry for such nodes

is set to infinity

 Path vector routing

• Similar to distance vector protocol
• In order to avoid the count to infinity problem, nodes also include path

information in their update messages

A E D C B F

2 2 1 3 1 1 2 5 3 5

B costs 2 C costs ∞ D costs ∞ E costs ∞ F costs ∞

10 ilab: Dynamic Routing

Link-State Routing

Approach



Information gathering

• Nodes are aware of the network

topology due to the broadcasting of link properties



Path calculation

• Each node calculates its own shortest

path tree (itself being the root of the tree)

• Algorithm used:

Dijkstra or Bellman-Ford

• Derive routing table from shortest

path tree



Result: Routing table

A E D C B F

2 2 1 3 1 1 2 5 3 5

Flooding

A E D C B F

2 1 1 2 1

Shortest Path tree B B C-F D to via

11 ilab: Dynamic Routing

Forward-Search Algorithm

 In practice, nodes use a forward search alogorithm based on the

• riginal algorithm of Dijkstra

 All nodes flood the network with their Link State Packets (LSP)  Nodes maintain a tentative and a confirmed list and calculate the

routing table directly after receiving the LSPs A C B

2 4 1 8 3

D

12 ilab: Dynamic Routing

Example for node D

Step 1 2 3 4 5 6 7 confirmed (D,0,-) (D,0,-) (D,0,-) (A,1,A) (D,0,-) (A,1,A) (D,0,-) (A,1,A) (B,3,A) (D,0,-) (A,1,A) (B,3,A) (D,0,-) (A,1,A) (B,3,A) (C,6,A) tentativ (A,1,A) (B,4,B) (C,8,C) (B,4,B) (C,8,C) (B,3,A) (C,8,C) (C,8,C) (C,6,A) Notes Read LSP of D populate tentative list Add the least expensive entry to the confirmed list (here A) Read its LSP and update the entries (here: path to B) Add the least expensive entry to the confirmed list Read its LSP and update the entries (here: route to C) Add the least expensive entry to the confirmed list

A C B

2 4 1 8 3

D

13 ilab: Dynamic Routing

Routing in the internet

14 ilab: Dynamic Routing 14

Autonomous System

 Autonomes System (AS): Networks under one administrative

• rganization
• e.g. provider network, campus network

 Changes within the AS not relevant for other systems

• Internal structure
• But also: routing protocol

 Each AS may have a different internal routing protocol  Routing between AS‘s: inter-domain routing protocols  Each AS is identified by a 16bit AS number

15 ilab: Dynamic Routing

Internet: autonomous systems

AS X AS A AS D AS Z AS B AS C

Inter-AS- connection

Border Router Autonomous System X

AS X

Stub-AS Multihomed AS

Transittraffic

16 ilab: Dynamic Routing

Dynamic routing in the internet

 Autonomous System (AS):

Networks under one administrative organization

 Interior Gateway (IG):

Internal routers of an AS

 Exterior Gateway (EG):

Border routers Core Network EG EG IG IG IG IG

AS AS

IG

Interior Gateway Protocols (IGP) Exterior Gateway Protocols (EGP) Routing in the internet

• Exterior Gateway Protocol (EGP) - outdated
• Border Gateway Protocol (BGP)
• Routing Information Protocol (RIP)
• Open Shortest Path First (OSPF)

17 ilab: Dynamic Routing

Real Routing protocols

 Intra-Domain-Routing:

• OSPF (Open Shortest Path First)
• IAB recommended protocol
• „Link State“ protocol
• RIP (Routing Information Protocol) – for small networks
• Less robust (routing loops)
• Slower reaction on link changes
• Distance vector protocol
• IGRP: Interior Gateway Routing Protocol (Cisco propr.)

 Inter-Domain-Routing:

• BGP (Border Gateway Protocol)
• Path vector protocol
• BGP Version 4 (BGP4) also supports Classless Inter-Domain Routing

(CIDR)

18 ilab: Dynamic Routing

RIP ( Routing Information Protocol)



Distance-Vektor-Verfahren



since 1982 in BSD-UNIX



Metric: # of Hops (max = 15 Hops)



Distance vectors: updates/advertisements are sent every 30s via UDP



Each advertisement contains routes to max. 25 destination networks



Link declared unreachable after 180s without an update

• Routes via this neighbor are considered invalid
• New advertisements have to be sent to all neighboring nodes
• Sende neue Advertisements zu den Nachbarn
• Neighbors also send new advertisements on changes
• Poison-Reverse to avoid loops (infinity = 16 hops)

19 ilab: Dynamic Routing

OSPF (Open Shortest Path First)

 Link-State-Protocol  OSPF-Advertisements contain one entry per neighboring node  Advertisements are flooded to the whole AS  Security: all OSPF messages are authenticated  Hierarchical OSPF for large AS

20 ilab: Dynamic Routing

Hierarchical OSPF

21 ilab: Dynamic Routing

BGP

 BGP (Border Gateway Protocol)  Standard protocol in the internet  Path-Vector-Protocol:

• Similar to distance vector
• Each border gateway broadcasts its neighbors the entire path

(sequence of AS numbers)

 Neighbors decide based on policies and costs which path to use

• Real costs (peering contracts)

22 ilab: Dynamic Routing

Intra- vs. Inter-AS-Routing

 Policy:

• Inter-AS: Each administrator wants to control which traffic is routed

through the network

• Intra-AS: no need for policies

 Scalablity:

• Hierarchical routing reduces the size of the routing tables and the traffic

needed for exchanging routing information

 Performance:

• Intra-AS: focusses on performance
• Inter-AS: policies often more important than performance

23 ilab: Dynamic Routing

Now it is up to you! You heard about a lot of things today, Now get your own hands on them…

Have fun with the exercise!

See you next week at 10h15 in 03.07.023.