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
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
Outline Practice: Routing Prococols RIP OSPF BGP 2/45
Outline Meta Recap Background: Internet Architecture Theory: Routing Algorithms Practice: Routing Prococols 3/45
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
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
Outline Meta Recap Background: Internet Architecture Theory: Routing Algorithms Practice: Routing Prococols 6/45
Recap: Network Layer 7/45
Outline Meta Recap Background: Internet Architecture Internet Exchange Points (IXPs) Autonomous Systems Routing between ASes Theory: Routing Algorithms Practice: Routing Prococols 8/45
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
Example: DFN Network L2 Topology and PoPs X-WiN-Topologie: Glasfasern Glasfaser Bestand Kernnetzknoten Bestand Stand: Oktober 2018 Glasfasertopologie des X-WiN 1 Source: https://www.dfn.de/fileadmin/1Dienstleistungen/XWIN/Topologie.pdf 10/45
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
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
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
Example: The Google Edge Network Source: https://peering.google.com/#/infrastructure 14/45
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
DE-CIX Frankfurt: Topology Source: https://www.de-cix.net/about/topology/ 16/45
DE-CIX Frankfurt: Core Switch 17/45 Source: https://press.de-cix.net/graphics/
DE-CIX Frankfurt: Throughput (2 days) Source: https://www.de-cix.net/en/locations/germany/frankfurt/statistics 18/45
DE-CIX Frankfurt: Throughput (5 years) Source: https://www.de-cix.net/en/locations/germany/frankfurt/statistics 19/45
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
Terminology: Autonomous Systems 21/45
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
Outline Meta Recap Background: Internet Architecture Theory: Routing Algorithms Problem Definition Link-State Routing Distance-Vector Routing Practice: Routing Prococols 23/45
Static /. Dynamic Routing Static Routing manual construction of routing tables 24/45
Static /. Dynamic Routing Static Routing manual construction of routing tables • does not scale 24/45
Static /. Dynamic Routing Static Routing manual construction of routing tables • does not scale • does not react to changes (e.g. link failure) 24/45
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
Problem Definition • find a path from the source to the destination host B C SRC DST A F E D 25/45
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
Problem Definition cont’d • link metrics attribute cost to links: e.g. path length, reliability, delay, bandwidth, load, communication cost, or routing policies B C 3 2 5 2 SRC 1 DST 3 A F 1 2 1 E D 27/45
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) B C 3 2 5 2 1 3 A F 1 2 1 D E 28/45
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
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
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
Example: Dijkstra’s Algorithm for Router A B C 3 2 5 2 1 3 A F 1 2 1 D E N’ D(B), D(C), D(D), D(E), D(F), p(B) p(C) p(D) p(E) p(F) 32/45
Example: Dijkstra’s Algorithm for Router A B C 3 2 5 2 1 3 A F 1 2 1 D E 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
Example: Dijkstra’s Algorithm for Router A B C 3 2 5 2 1 3 A F 1 2 1 D E 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
Example: Dijkstra’s Algorithm for Router A B C 3 2 5 2 1 3 A F 1 2 1 D E 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
Example: Dijkstra’s Algorithm for Router A B C 3 2 5 2 1 3 A F 1 2 1 D E 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
Example: Dijkstra’s Algorithm for Router A B C 3 2 5 2 1 3 A F 1 2 1 D E 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
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