[PPT] - Internet Lab (iLabX) Dynamic Routing Christian Lbben PowerPoint Presentation

SLIDE 1

Chair of Network Architectures and Services Department of Informatics Technical University of Munich

Internet Lab (iLabX) Dynamic Routing

Christian Lübben ilabx@net.in.tum.de

Chair of Network Architectures and Services Department of Informatics Technical University of Munich

Lab 2 – WiSe 2019

SLIDE 2

Outline

Meta Recap Background: Internet Architecture Internet Exchange Points (IXPs) Autonomous Systems Routing between ASes Theory: Routing Algorithms Problem Definition Link-State Routing Distance-Vector Routing

1/45

SLIDE 3

Outline

Practice: Routing Prococols RIP OSPF BGP

2/45

SLIDE 4

Outline

Meta Recap Background: Internet Architecture Theory: Routing Algorithms Practice: Routing Prococols

3/45

SLIDE 5

Recordings

check that you can log in and access video recordings (media.net.in.tum.de)
slides are with the videos (media portal)
slides of previous term in prelab (e-learning system)
slides as-held after the lecture in ’Lecture Material’ (e-learning system)

4/45

SLIDE 6

Lecture Schedule Update

dynamic routing, TCP/UDP

, DNS delayed by one week

lab schedule is up to date
TUMonline schedule is not yet up to date
oral attestations NOT delayed

5/45

SLIDE 7

Outline

Meta Recap Background: Internet Architecture Theory: Routing Algorithms Practice: Routing Prococols

6/45

SLIDE 8

Recap: Network Layer

7/45

SLIDE 9

Outline

Meta Recap Background: Internet Architecture Internet Exchange Points (IXPs) Autonomous Systems Routing between ASes Theory: Routing Algorithms Practice: Routing Prococols

8/45

SLIDE 10

Example: Traceroute from TUM I8 to google.de

hops 1–4, Leibniz-Rechenzentrum (LRZ), AS12816
hops 5–6, Deutsches Forschungsnetz (DFN), AS680
hops 7–10, Google, AS15169

9/45

SLIDE 11

Example: DFN Network L2 Topology and PoPs

Glasfasertopologie des X-WiN 1

X-WiN-Topologie: Glasfasern

Glasfaser Bestand Kernnetzknoten Bestand

Stand: Oktober 2018

Source: https://www.dfn.de/fileadmin/1Dienstleistungen/XWIN/Topologie.pdf

10/45

SLIDE 12

Internet Architecture

Internet Topology

the Internet is a decentralized network of networks
many organizations operate their own network, which all need to be interconnected
glue: IP protocol, exchange of routing information (BGP)

Typical Network Operators

content providers
content delivery networks (CDN) support content providers
access providers (“eyeball networks”), content consumption
transit providers

11/45

SLIDE 13

Internet Architecture cont’d

Source: C. Labovitz, S. Iekel-Johnson, D. McPherson, J. Oberheide, and F . Jahanian. Internet inter-domain traffic. In Proceedings of the ACM SIGCOMM 2010 conference (SIGCOMM ’10)

12/45

SLIDE 14

Example: Top Content Providers in Oregon Univ. Network

Source: B. Yeganeh, R. Rejaie, W. Willinger. A view from the edge: A stub-AS perspective of traffic localization and its implications. TMA 2017

13/45

SLIDE 15

Example: The Google Edge Network

Source: https://peering.google.com/#/infrastructure

14/45

SLIDE 16

Background: Internet Exchange Points (IXPs) Definition

an exchange point for traffic between network operators
makes it easy to connect to many other networks (via peering)
provides physical infrastructure

Largest IXPs

DE-CIX (Frankfurt), see https://peeringdb.com/ix/31
AMS-IX (Amsterdam), see https://peeringdb.com/ix/26
LINX (London), see https://peeringdb.com/ix/18

Example fees (2016, DE-CIX Frankfurt)

1 Gbit/s costs 500 Euro/month
10 Gbit/s costs 1,550 Euro/month
100 Gbit/s costs 9,500 Euro/month

15/45

SLIDE 17

DE-CIX Frankfurt: Topology

Source: https://www.de-cix.net/about/topology/

16/45

SLIDE 18

DE-CIX Frankfurt: Core Switch

Source: https://press.de-cix.net/graphics/

17/45

SLIDE 19

DE-CIX Frankfurt: Throughput (2 days)

Source: https://www.de-cix.net/en/locations/germany/frankfurt/statistics

18/45

SLIDE 20

DE-CIX Frankfurt: Throughput (5 years)

Source: https://www.de-cix.net/en/locations/germany/frankfurt/statistics

19/45

SLIDE 21

Connecting Autonomous Systems Definition: Autonomous System (AS)

networks under a common administrative organization

e.g. ISP network, campus network

an AS is identified by a 32bit AS-number

(was extended from 16bit in 2007)

each AS advertises the address space it is willing to accept

(belonging to the AS itself or as transit traffic)

Implications

from the outside, ASes are viewed as a single entity with border routers and a routed address space
changes within an AS are not relevant for other ASes

e.g. internal topology, intra-AS routing

all ASes must agree on a common way of exchanging routing information, inter-AS routing

20/45

SLIDE 22

Terminology: Autonomous Systems

21/45

SLIDE 23

Intra-AS ./ Inter-AS-Routing Route selection

intra-AS routing: focus on best paths
inter-AS routing: also follow business policies

⇒ different link metrics and filtering policies

Scalability

border routers need to deal with a large number of routing table entries

IPv4: 800k entries
IPv6: 60k entries

22/45

SLIDE 24

Outline

Meta Recap Background: Internet Architecture Theory: Routing Algorithms Problem Definition Link-State Routing Distance-Vector Routing Practice: Routing Prococols

23/45

SLIDE 25

Static /. Dynamic Routing Static Routing

manual construction of routing tables

24/45

SLIDE 26

Static /. Dynamic Routing Static Routing

manual construction of routing tables

does not scale

24/45

SLIDE 27

Static /. Dynamic Routing Static Routing

manual construction of routing tables

does not scale
does not react to changes (e.g. link failure)

24/45

SLIDE 28

Static /. Dynamic Routing Static Routing

manual construction of routing tables

does not scale
does not react to changes (e.g. link failure)

Dynamic Routing

distributed algorithms automate the construction of routing tables

scales depending on the algorithm
automated routing table updates after topology changes (with a certain delay)

24/45

SLIDE 29

Problem Definition

find a path from the source to the destination host

D B C E F A

SRC DST

25/45

SLIDE 30

Problem Definition cont’d

each hop (i.e. router or AS) forwards a packet closer to its

destination based on the information in its FIB

SRC DST

26/45

SLIDE 31

Problem Definition cont’d

link metrics attribute cost to links:

e.g. path length, reliability, delay, bandwidth, load, communication cost, or routing policies

D B C E F A

SRC DST

2 3 5 2 1 3 1 2 1

27/45

SLIDE 32

Problem Definition cont’d

routing can be reduced to a graph problem

each node represents a router
each edge represents a link
each link comes with a certain cost, c(X,Y)

D B C E F A

2 3 5 2 1 3 1 2 1

28/45

SLIDE 33

Routing Protocols

Distributed routing algorithms perform the following steps

1. gather information about the network topology
2. create the local routing table based on the gathered information

Common Routing Protocols and Algorithms

OSPF, IS-IS (Link-State Routing)
RIP (Distance-Vector Routing)
BGP (Path-Vector Routing)

29/45

SLIDE 34

Link-State Routing Information propagation

each router exchanges link-state updates with each other router in the network (flooding)
link-state updates contain list of adjacent routers and networks including costs

⇒ each router knows the whole network topology (global view)

Information processing

each router calculates the shortest paths to every other destination, e.g. using Dijkstra’s algorithm
derive routing table from shortest path tree

Implementations

OSPF, IS-IS

30/45

SLIDE 35

Dijkstra’s Algorithm with Source Node u

Initialization : N' = {u} # visited nodes for all nodes v if v is neighbor of u then D(v) = c(u,v) else D(v) = ∞ Loop find w not in N' such that D(w) is minimum add w to N' for each neighbor v of w if v not in N': D(v) = min( D(v), D(w) + c(w,v) ) until N' = N

31/45

SLIDE 36

Example: Dijkstra’s Algorithm for Router A

D B C E F A

2 3 5 2 1 3 1 2 1

N’ D(B), D(C), D(D), D(E), D(F), p(B) p(C) p(D) p(E) p(F)

32/45

SLIDE 37

Example: Dijkstra’s Algorithm for Router A

D B C E F A

2 3 5 2 1 3 1 2 1

N’ D(B), D(C), D(D), D(E), D(F), p(B) p(C) p(D) p(E) p(F) A 2,A ∞ 1,A ∞ ∞

32/45

SLIDE 38

Example: Dijkstra’s Algorithm for Router A

D B C E F A

2 3 5 2 1 3 1 2 1

N’ D(B), D(C), D(D), D(E), D(F), p(B) p(C) p(D) p(E) p(F) A 2,A ∞ 1,A ∞ ∞ A,D 2,A 4,D 2,D ∞

32/45

SLIDE 39

Example: Dijkstra’s Algorithm for Router A

D B C E F A

2 3 5 2 1 3 1 2 1

N’ D(B), D(C), D(D), D(E), D(F), p(B) p(C) p(D) p(E) p(F) A 2,A ∞ 1,A ∞ ∞ A,D 2,A 4,D 2,D ∞ A,D,E 2,A 3,E 4,E

32/45

SLIDE 40

Example: Dijkstra’s Algorithm for Router A

D B C E F A

2 3 5 2 1 3 1 2 1

N’ D(B), D(C), D(D), D(E), D(F), p(B) p(C) p(D) p(E) p(F) A 2,A ∞ 1,A ∞ ∞ A,D 2,A 4,D 2,D ∞ A,D,E 2,A 3,E 4,E A,D,E,B 3,E 4,E

32/45

SLIDE 41

Example: Dijkstra’s Algorithm for Router A

D B C E F A

2 3 5 2 1 3 1 2 1

N’ D(B), D(C), D(D), D(E), D(F), p(B) p(C) p(D) p(E) p(F) A 2,A ∞ 1,A ∞ ∞ A,D 2,A 4,D 2,D ∞ A,D,E 2,A 3,E 4,E A,D,E,B 3,E 4,E A,D,E,B,C 4,E

32/45

SLIDE 42

Example: Dijkstra’s Algorithm for Router A

D B C E F A

2 3 5 2 1 3 1 2 1

N’ D(B), D(C), D(D), D(E), D(F), p(B) p(C) p(D) p(E) p(F) A 2,A ∞ 1,A ∞ ∞ A,D 2,A 4,D 2,D ∞ A,D,E 2,A 3,E 4,E A,D,E,B 3,E 4,E A,D,E,B,C 4,E A,D,E,B,C,F

32/45

SLIDE 43

Distance-Vector Routing Information propagation

each router exchanges advertisements with its neighbors
advertisements contain a snapshot of the current routing table (as distance vectors) of the source

router ⇒ the routers only have limited information about the network topology (local view)

Information processing

each router keeps distance vectors to all other routers
compute new distance vector on incoming advertisement
derive routing table from distance vectors

Implementations

RIP

, BGP (path-vector)

33/45

SLIDE 44

Distance Vector Algorithm Bellman-Ford equation:

Dx(y) = minv(c(x, v) + Dv(y)) minimum distance from x to y Initialization : for all nodes x,y in N Dx(y) = c(x,y) if y is neigbor of x Dx(y) = ∞ else Loop forever: for all neighbors v of x: Dx(y) = minv(c(x,v) + Dv(y)) if Dx(y) changed: send Dx(y) to all neighbors

34/45

SLIDE 45

Example: Distance Vector Algorithm

X Y Z

7 2 1

node: X Y Z cost to: X Y Z X Y Z X Y Z from X: 2 7 ∞ ∞ ∞ ∞ ∞ ∞ from Y: ∞ ∞ ∞ 2 1 ∞ ∞ ∞ from Z: ∞ ∞ ∞ ∞ ∞ ∞ 7 1

35/45

SLIDE 46

Example: Distance Vector Algorithm

X Y Z

7 2 1

(0, 2, 7) (0, 2, 7)

node: X Y Z cost to: X Y Z X Y Z X Y Z from X: 2 7 2 7 2 7 from Y: ∞ ∞ ∞ 2 1 ∞ ∞ ∞ from Z: ∞ ∞ ∞ ∞ ∞ ∞ 7 1

35/45

SLIDE 47

Example: Distance Vector Algorithm

X Y Z

7 2 1

(2, 0, 1) (2, 0, 1)

node: X Y Z cost to: X Y Z X Y Z X Y Z from X: 2 3 2 7 2 7 from Y: 2 1 2 1 2 1 from Z: ∞ ∞ ∞ ∞ ∞ ∞ 3 1

35/45

SLIDE 48

Example: Distance Vector Algorithm

X Y Z

7 2 1

(3, 1, 0) (3, 1, 0)

node: X Y Z cost to: X Y Z X Y Z X Y Z from X: 2 3 2 7 2 7 from Y: 2 1 2 1 2 1 from Z: 3 1 3 1 3 1

35/45

SLIDE 49

Example: Distance Vector Algorithm

X Y Z

7 2 1

(0, 2, 3) (0, 2, 3)

node: X Y Z cost to: X Y Z X Y Z X Y Z from X: 2 3 2 3 2 3 from Y: 2 1 2 1 2 1 from Z: 3 1 3 1 3 1

35/45

SLIDE 50

Example: Distance Vector Algorithm

X Y Z

7 2 1

node: X Y Z cost to: X Y Z X Y Z X Y Z from X: 2 3 2 3 2 3 from Y: 2 1 2 1 2 1 from Z: 3 1 3 1 3 1

35/45

SLIDE 51

Example: Routing Table Computation

node: X Y Z cost to: X Y Z X Y Z X Y Z from X: 2 3 2 3 2 3 from Y: 2 1 2 1 2 1 from Z: 3 1 3 1 3 1 From which router was the best route learned? node: X Y Z cost to: X Y Z X Y Z X Y Z via X: 2 4 5 7 9 10 via Y: 4 2 3 3 1 2 via Z: 10 8 7 4 2 1 e.g. routing table of router X: networks announced by router Y: next hop Y (cost 2), networks announced by router Z: next hop Y (cost 3)

36/45

SLIDE 52

Example: Count-to-Infinity Problem

X Y Z

7 50 1

node: Y Z cost to: X Y Z X Y Z from X: 2 3 2 3 from Y: 4 1 2 1 from Z: 3 1 3 1

37/45

SLIDE 53

Example: Count-to-Infinity Problem

X Y Z

7 50 1

(4, 0, 1) (4, 0, 1)

node: Y Z cost to: X Y Z X Y Z from X: 2 3 2 3 from Y: 4 1 4 1 from Z: 3 1 5 1

37/45

SLIDE 54

Example: Count-to-Infinity Problem

X Y Z

7 50 1

(5, 1, 0) (5, 1, 0)

node: Y Z cost to: X Y Z X Y Z from X: 2 3 2 3 from Y: 6 1 4 1 from Z: 5 1 5 1

37/45

SLIDE 55

Example: Count-to-Infinity Problem

X Y Z

7 50 1

(6, 0, 1) (6, 0, 1)

node: Y Z cost to: X Y Z X Y Z from X: 2 3 2 3 from Y: 6 1 6 1 from Z: 5 1 7 1

37/45

SLIDE 56

Count-to-Infinity Countermeasures Distance-Vector with Poisoned Reverse

if the shortest path to a destination Y was learned from neighbor Z, then set DX(Y) = ∞ in updates to

neighbor Z

Path-Vector Routing

Update messages contain full path, this allows loop-detection
e.g. ([0,B], [4,"D,E,A"], [1,"E,F"])

38/45

SLIDE 57

Example: Poisoned Reverse

X Y Z

7 50 1

node: Y Z cost to: X Y Z X Y Z from X: 2 3 2 3 from Y: 4 1 2 1 from Z: 3 1 3 1

39/45

SLIDE 58

Example: Poisoned Reverse

X Y Z

7 50 1

(∞, 0, 1) (∞, 0, 1)

node: Y Z cost to: X Y Z X Y Z from X: 2 3 2 3 from Y: 4 1 7 1 from Z: 3 1 ∞ 1

39/45

SLIDE 59

Example: Poisoned Reverse

X Y Z

7 50 1

(7, 1, 0) (7, 1, 0)

node: Y Z cost to: X Y Z X Y Z from X: 2 3 2 3 from Y: 8 1 7 1 from Z: 7 1 ∞ 1

39/45

SLIDE 60

Distance-Vector (DV) ./ Link-State Routing (LS) Scalibility

LS floods the network
DV nodes only talk to their neighbors

Speed of convergence

LS converges fast
DV can converge slowly, e.g. count-to-infinity problem

routing loops may occur temporarily

40/45

SLIDE 61

Outline

Meta Recap Background: Internet Architecture Theory: Routing Algorithms Practice: Routing Prococols RIP OSPF BGP

41/45

SLIDE 62

Routing Information Protocol (RIP)

RIPv2, RIPng (supports IPv6)

Basics

interior gateway protocol (IGP)
distance-vector algorithm
link metric: number of hops (link cost= 1, ∞ = 16)
implements poisoned reverse

Routing updates

UDP port 520
RIP response messages are sent periodically (every 30s) or on changes
link is declared unreachable after 180s without an update
each advertisement contains routes to max. 25 destinations

42/45

SLIDE 63

Open Shortest Path First (OSPF)

conceived as the successor to RIP

, some advanced features

OSPFv3 adds support for IPv6 (2008)

Basics

interior gateway protocol (IGP)
link-state algorithm
multiple same-cost paths
supports hierarchy through definition of areas
messages can be authenticated

Routing updates

IP datagrams with protocol number 89, multicast addressing
can be authenticated

43/45

SLIDE 64

Border Gateway Protocol (BGP) Background

BGP is the de facto inter-AS routing protocol in the Internet
BGPv4 was introduced in 1994
extensible to implement new functions
built to scale
implements policy-based routing

Basics

path-vector algorithm (path is a sequece of AS numbers)
uses periodic keepalives and incremental updates

44/45

SLIDE 65

Border Gateway Protocol (BGP) cont’d. Routing updates

TCP port 179
eBGP spreads inter-AS routing information between ASes
iBGP spreads inter-AS routing information within an AS
path is a sequence of AS numbers

Problems

routing table growth (>800.000 IPv4 entries)
load balancing in multihomed ASes
security: BGP prefix hijacking

e.g. https://www.ripe.net/publications/news/industry-developments/youtube-hijacking-a-ripe-ncc-ris-case-study

45/45