Internet Routing Protocols Lecture 01 Advanced Systems Topics Lent Term, 2008 Timothy G. Griffin Computer Lab Cambridge UK Common View of the Telco Network Brick 1 Common View of the IP Network (Layer 3) IP routing is the little bit-o-smarts left in the IP network layer • Dynamic Routing protocols are used to implement and maintain connectivity in the Internet. • Which protocols are used? • How do they work? • How do they behave? • What are some of the fundamental tradeoffs in the design space of routing protocols? 2 Outline • Lecture 1 : Routing vs. Forwarding. Internet routing architecture • Lecture 2: Intra-domain routing with “shortest paths”. Link-state vs. distance- vector. • Lecture 3 : Inter-domain routing. The Border Gateway Protocol (BGP) • Lecture 4 : BGP continued • Lecture 5 : BGP dynamics • Lecture 6 : BGP routing anomalies 3 4 GARR-B 5 wiscnet.net UW-Superior Rice Lake Rhinelander Stiles UW-Stout Wausau Jct. UW-River Falls Marshfield UW-Eau Claire Clintonville er '02) (Summ Qwest UW-Stevens Point and Other UW-Green Bay (Sum Provider(s) mer '02) Fox Valley TC (S ( u S m u m UW-Oshkosh m e r m ' 0 e 2 UW-La Crosse r ) ' 0 3 La Crosse ) Portage Internet 2 & Qwest Dodgeville Genuity UW-Madison (Summer '03) UW-Milwaukee GO BUCKY! ( UW-Whitewater W UW-Parkside UW-Platteville i n t e r Gigabit Ethernet ' 0 2 OC-12 (622Mbps) ) OC-3 (155Mbps) Chicago ! Peering - Public and Private 2) r '0 Chicago - 2 DS-3 (45Mbps) ! Commodity Internet Transit inte (W (Winter '02) ! Internet2 T1 (1.5Mbps) ! Merit and Other State Networks Chicago - 1 ! National Education Network ! Regional Research Peers 6 WorldCom (UUNet) Internet Initiative Japan (IIJ) 7 Telstra international Anchorage, AK AT&T IP Backbone Year end 2001 Seattle Spokane Portland Worcester Portland Manchester Minneapolis Albany R St. Paul Glenvie Syracuse Rochester Cambridge Milwaukee w Hartford Framingham Madison Grand Wayne Rolling Rapids Birmingham Buffalo R Stamford PProrovvidideennccee Meadows R Bridgepor Detroit Harrisburg t Des Moines New Brunswick NYC White Oak Plains Salt Lake Davenport Plymouth Phil Cedar Knolls Brook Pittsburgh Sacramento City Chicago Wash. Rochelle Pk R Cleveland Akron San South Bend Hamilton R R Omaha DC San Las Chicago Silver R Square Francisco Denver Dayto Columbus Newark Francisco Vegas n Springs Baltimore Freehold Kansas Indianapolis Bohemia City Arlington R Cincinnati R NYC- Bdwy Oakland Florissant Norfolk San Jose Colorado Camden, St Louis NJ R Springs Louisville Richmond Redwood R City Raleigh Sherman OakLs os Angeles Albuquerque Oklahom Nashville Greensboro a Tulsa Charlotte Honolulu San City Bernardino LA-Airport Blvd Little Rock Anaheim Memphis Garden Birmingham Columbia a Phoenix Norcross Dunwoody San Diego Gateway Node Atlanta Ft. Worth Dallas Backbone Node Jacksonville Remote GSR Access Router New Orleans R Austin Orlando Remote Access Router Houston San Antonio R N X DS3 Tampa W. Palm Beach Note: Connectivity and N X OC3 nodes shown are R Ft. Lauderdale Ft. Ojus targeted for deployment; Lauderdale N X OC12 actual deployment Miami N X OC48 San Juan PR may vary. Maps should NX OC192 not be used to predict service availability. Rev. 6-4-01 8 Architecture of Dynamic Routing IGP BGP AS 1 IGP = Interior Gateway Protocol. Metric based. IGP OSPF, IS-IS, RIP, EIGRP (cisco) AS 2 EGP = Exterior Gateway Protocol. Policy Based. Only one: BGP The Routing Domain of BGP is the entire Internet How many ASN are used today? http://bgp.potaroo.net Jan 28. 2008 9 Routers Talking to Routers (The “control plane”) Routing info Routing info • Routing computation is distributed among routers within a routing domain • Computation of best next hop based on routing information is the most CPU/memory intensive task on a router • Routing messages are usually not routed, but exchanged via layer 2 between physically adjacent routers (internal BGP and multi-hop external BGP are exceptions) Technology of Distributed Routing Link State Vectoring • Topology information is • Each router knows little about flooded within the routing network topology domain • Only best next-hops are chosen • Best end-to-end paths are by each router for each destination network. computed locally at each router. • Best end-to-end paths result • Best end-to-end paths from composition of all next- determine next-hops. hop choices • Based on minimizing some • Does not require any notion of notion of distance distance • Works only if policy is shared • Does not require uniform and uniform policies at all routers • Examples: OSPF, IS-IS • Examples: RIP, BGP 10 The Gang of Four Link State Vectoring OSPF IGP RIP IS-IS EGP BGP The standard model data received data sent Application Application Presentation Presentation Session Session Transport Transport Network Network DataLink DataLink Physical Physical 22 11 All Hail the IP Datagram! 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ H |Version| IHL | Service Type | Total Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ E | Identification |Flags| Fragment Offset | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ A | Time to Live | Protocol | Header Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ D | Source Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ E | Destination Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ R | Options | Padding | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ : : D : : | | A + ... up to 65,515 octets of data ... + | | T + + | | A +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 23 shaded fields little-used today 1981, RFC 791 IP Hour Glass Networking Applications Remote Access Voice e-stuff email file transfer Multimedia Web TCP VPN IP Minimalist network layer Frame ATM Ethernet SONET DWDM X.25 FDDI Networking Technologies 24 12 Best Effort, Connectionless, Connectivity IP traffic 135.207.49.8 192.0.2.153 The is the fundamental service provided by Internet Service Providers (ISPs) All other IP services depend on connectivity: DNS, email, VPNs, Web Hosting, … IP is a Network Layer Protocol Separate physical networks glued together into one Application logical network Application Presentation Router Presentation Session Session Transport Transport Network Network Network DataLink 1 DataLink 1 DataLink 2 DataLink 2 Physical 1 Physical 1 Physical 2 Physical 2 Medium 1 Medium 2 26 13 Hosts, Networks, and Routers Host 7 Host 1 Network A Host 2 Host 1 Router Network C Network B Unique IP Address = Network Number + Host Number Host 12 Host 2 27 Actually, IP addresses Identify Interfaces Host 7 Host 1 Network A Network C, Host 3 Network A, Host 2 Host 1 Host 3 Network B, Network C Network B Host 77 Machines can have more than one IP address. Host 12 Host 2 All routers do! 28 14 IP Forwarding Table Destination Next Hop Interface Net A Router 1 INT 7 Net B Direct INT 4 Net C, Host 3 Router 2 INT 3 Net C Router 1 INT 7 A destination is usually The next hop is A physical interface a network. May also be either a directly a host, or a “gateway connected network or a of last resort” (default) router on a directly 29 connected network IP Forwarding Process 1. Remove a packet 2. Check for sanity, 4. Place packet on from an input decrement TTL correct output queue field queue Forwarding Process 3. Match packet’s If queues If queues destination to get full, just get full, just a table entry drop packets! drop packets! IP Forwarding Table Router 30 15 IPv4 Addresses are 32 Bit Values 11111111 00010001 10000111 00000000 255 17 134 0 255.17.134.0 Dotted quad notation IPv6 addresses have 128 bits 31 IP Addresses come in two parts 11111111 00010001 10000111 00000000 Network Number Host Number Where is this dividing line? Well, that depends .... 32 16 Classful Addresses Class A 0nnnnnnn hhhhhhhh hhhhhhhh hhhhhhhh Class B 10nnnnnn nnnnnnnn hhhhhhhh hhhhhhhh Class C 110nnnnn nnnnnnnn nnnnnnnn hhhhhhhh n = network address bit h = host identifier bit Leads to a rigid, flat, inefficient use of address space … 33 RFC 1519: Classless Inter-Domain Routing (CIDR) Use two 32 bit numbers to represent a network. Network number = IP address + Mask IP Address : 12.4.0.0 IP Mask: 255.254.0.0 Address 00001100 00000100 00000000 00000000 Mask 11111111 11111110 00000000 00000000 Network Prefix for hosts Usually written as 12.4.0.0/15 34 17 Which IP Addresses are Covered by a Prefix? 12.5.9.16 is covered by prefix 12.4.0.0/15 12.5.9.16 00001100 00000101 00001001 00010000 00001100 00000100 00000000 00000000 12.4.0.0/15 11111111 11111110 00000000 00000000 12.7.9.16 00001100 00000111 00001001 00010000 12.7.9.16 is not covered by prefix 12.4.0.0/15 CIDR allows Hierarchy in Addressing 12.0.0.0/16 : 12.1.0.0/16 12.3.0.0/24 12.2.0.0/16 12.3.1.0/24 : 12.3.0.0/16 : : : 12.0.0.0/8 : 12.3.254.0/24 : 12.253.0.0/19 : 12.253.32.0/19 12.253.64.0/19 12.253.0.0/16 12.253.96.0/19 12.254.0.0/16 12.253.128.0/19 12.253.160.0/19 12.253.192.0/19 36 18 Classless Forwarding Destination =12.5.9.16 ------------------------------- payload Prefix Next Hop Interface OK 0.0.0.0/0 10.14.11.33 ATM 5/0/9 better 12.0.0.0/8 10.14.22.19 ATM 5/0/8 even better 12.4.0.0/15 10.1.3.77 Ethernet 0/1/3 best! 12.5.8.0/23 attached Serial 1/0/7 IP Forwarding Table How Are Forwarding Tables Populated to implement Routing? Statically Dynamically Administrator Routers exchange network reachability manually configures information using ROUTING PROTOCOLS. forwarding table entries Routers use this to compute best routes + More control + Can rapidly adapt to changes + Not restricted to in network topology destination-based + Can be made to scale well forwarding - Complex distributed algorithms - Doesn’t scale - Consume CPU, Bandwidth, Memory - Slow to adapt to - Debugging can be difficult network failures - Current protocols are destination-based In practice : a mix of these.