Masterkurs Rechnernetze IN2097

Transcription

1 Masterkurs Rechnernetze IN2097 Advanced computer networking Internet Protocols Prof. Dr.-Ing. Georg Carle, Wolfgang Mühlbauer Chair for Network Architectures and Services Computer Science Department Technical University Munich

2 Outline Routing hierarchy Internet structure External BGP (E-BGP) Internal BGP (I-BGP) IN2097: Masterkurs Rechnernetze 2

3 Acknowledgements Randy H. Katz Distinguished professor at UCB thirteeen best paper awards Textbook: Contemporary Logic Design, has sold over 100,000 copies in two editions, and has been used at over 200 colleges and universities the late 1980s, with colleagues at Berkeley, he developed Redundant Arrays of Inexpensive Disks (RAID) Prior research interests have included: database management, VLSI CAD, high performance multiprocessor (Snoop cache coherency protocols) and storage (RAID) architectures, transport (Snoop TCP) and mobility protocols spanning heterogeneous wireless networks, and converged data and telephony network and service architectures. IN2097: Masterkurs Rechnernetze 3

4 Routing Hierarchies Flat routing doesn t scale Storage Each node cannot be expected to store routes to every destination (or destination network) Convergence times increase Communication Total message count increases Key observation Need less information with increasing distance to destination Need lower diameters networks Solution: area hierarchy IN2097: Masterkurs Rechnernetze 4

5 Areas Divide network into areas Areas can have nested subareas Constraint: no path between two sub-areas of an area can exit that area Hierarchically address nodes in a network Sequentially number top-level areas Sub-areas of area are labeled relative to that area Nodes are numbered relative to the smallest containing area IN2097: Masterkurs Rechnernetze 5

6 Routing Hierarchy Area-Border Router Backbone Areas Lower-level Areas Partition Network into Areas Within area Each node has routes to every other node Outside area Each node has routes for other top-level areas only Inter-area packets are routed to nearest appropriate border router Constraint: no path between two sub-areas of an area can exit that area IN2097: Masterkurs Rechnernetze 6

7 Routing Within area Each node has routes to every other node Outside area Each node has routes for other top-level areas only Inter-area packets are routed to nearest appropriate border router Can result in sub-optimal paths IN2097: Masterkurs Rechnernetze 7

8 Path Sub-optimality start end hop red path vs. 2 hop green path IN2097: Masterkurs Rechnernetze 8

9 A Logical View of the Internet National (Tier 1 ) Settlement-free and Default-free with global reachability info Eg: AT & T, UUNET, Sprint Regional (Tier 2 ) Regional or country-wide Eg: Pacific Bell Local (Tier 3 ) Eg: Telerama DSL Tier 3 Tier 2 Customer Provider Tier 2 Tier 1 Tier 1 Tier 2 IN2097: Masterkurs Rechnernetze 9

10 Outline Routing hierarchy Internet structure External BGP (E-BGP) Internal BGP (I-BGP) IN2097: Masterkurs Rechnernetze 10

11 Internet s Area Hierarchy Autonomous System (AS)? A set of routers under a single technical administration, using an interior gateway protocol (IGP) and common metrics to route packets within the AS and using an exterior gateway protocol (EGP) to route packets to other AS s Each AS assigned unique ID AS s peer at network exchanges IN2097: Masterkurs Rechnernetze 11

12 History: IGP Most common IGPs: RIP: Routing Information Protocol (v1: 1988, v2: 1994) OSPF: Open Shortest Path First ( ) IS-IS: Intermediate system to intermediate system (mid to end 90s) EIGRP: Enhanced Interior Gateway Routing Protocol (Cisco proprietary, mid-80s) IN2097: Masterkurs Rechnernetze 12

13 History: EGP Mid-80s: EGP Reachability protocol (no shortest path) Did not accommodate cycles (tree topology) Evolved when all networks connected to NSF backbone Result: BGP introduced as routing protocol Latest version = BGP 4 BGP-4 supports CIDR Primary objective: connectivity not performance IN2097: Masterkurs Rechnernetze 13

14 A Logical View of the Internet Tier 1 Default-free with global reachability info Tier 2 Regional or countrywide Tier 3 Local Tier 3 Tier 2 Tier 2 Customer Provider Tier 1 Tier 1 Tier 2 IN2097: Masterkurs Rechnernetze 14

15 Internet structure: network of networks roughly hierarchical at center: tier-1 s (e.g., Verizon, Sprint, AT&T, Cable and Wireless), national/international coverage treat each other as equals Tier-1 providers interconnect (peer) privately Tier 1 Tier 1 Tier 1 IN2097: Masterkurs Rechnernetze 15

16 . Tier-1 : e.g., Sprint POP: point-of-presence to/from backbone peering to/from customers IN2097: Masterkurs Rechnernetze 16

17 Internet structure: network of networks Tier-2 s: smaller (often regional) s Connect to one or more tier-1 s, possibly other tier-2 s Tier-2 pays tier-1 for connectivity to rest of Internet Tier-2 Tier 1 Tier-2 Tier-2 s also peer privately with each other. Tier-2 is customer of tier-1 provider Tier 1 Tier 1 Tier-2 Tier-2 Tier-2 IN2097: Masterkurs Rechnernetze 17

18 Internet structure: network of networks Tier-3 s and s last hop ( access ) network (closest to end systems) Local and tier- 3 s are customers of higher tier s connecting them to rest of Internet Tier 3 Tier-2 Tier 1 Tier-2 Tier 1 Tier-2 Tier 1 Tier-2 Tier-2 IN2097: Masterkurs Rechnernetze 18

19 Internet structure: network of networks a packet passes through many networks! Tier 3 Tier-2 Tier-2 Tier 1 Tier 1 Tier-2 Tier 1 Tier-2 Tier-2 IN2097: Masterkurs Rechnernetze 19

20 Transit vs. Peering Transit ($$ 1/2) P Transit ($$$) Y Transit ($) Transit ($$$) Transit ($) Z Peering Transit ($$) Transit ($$$) X Transit ($$) IN2097: Masterkurs Rechnernetze 20