How the Internet works? The Border Gateway Protocol (BGP)

Transcription

1 Chair of Network Architectures and Services - Prof. Carle Department of Computer Science Technical University of Munich How the Internet works? The Border Gateway Protocol (BGP) Edwin Cordeiro ilab2 Lecture SS 2017 Technical University of Munich (TUM) Department of Informatics Chair of Network Architectures and Services

2 Outline Routing and Forwarding RIB and FIB Path Vector Protocols Border Gateway Protocol (BGP) Business Considerations and Policy routing BGP Table Considerations Internet Exchange Points (IXP) Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

3 Routing Forwarding Routing: The process of determining the best path for specific types of packets (usually: all packets with the same destination) through the network (Traditionally) performed jointly by the routers of a network by exchanging messages Analogy: Read street map, plan journey Forwarding: The process where a router relays a packet to a neighbouring router. Selection of the neighbouring router depends on the previous routing protocol calculations Performed by one router on one packet Analogy: Read a street sign and determine if we should take the next exit In practice, this distinction is often ignored If router A routes packet X, then Actually, it doesn t it forwards X. Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

4 Routing Information Base (RIB) Forwarding Information Base (RIB) Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

5 Path Vector Protocols For each destination, advertise entire path (= sequence of node identifiers) to neighbours Cost calculation can be done by looking at path Count number of hops on the path Avoid paths containing some specific nodes Cheapest or most reliable route can be chosen Easy loop detection: Does my node ID already appear in the path? Notice: Distance Vector Protocols (choose cheapest path based on link cost ) and Link State Protocols (choose based on knowledge of all links of the network) will not be covered here Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

6 Hierarchical Routing Aggregate routers into regions called autonomous systems (short: AS; plural: ASes) One AS is usually a network under central control i.e. one ISP / big company Routers in same AS run a routing protocol = intra-as routing protocol (also called intradomain ) ASes are connected: via gateway routers Direct link to [gateway] router in another AS = inter-as routing protocol (also called interdomain ) Warning: Non-gateway routers need to know about inter-as routing as well! Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

7 Inter-AS Routing Suppose router in AS1 receives datagram destined outside of AS1: Router should forward packet to gateway router but to which one? AS1 must: 1. learn which destinations are reachable through AS2, which through AS3 2. propagate this reachability info to all routers in AS1 (i.e., not just the gateway routers) Job of inter-as routing! 3c 3b AS3 3a 1a 1c 1d 1bAS1 2a AS2 2c 2b Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

8 Example: Choosing among multiple ASes Now suppose AS1 learns from inter-as protocol that subnet x is reachable from AS3 and from AS2. To configure forwarding table, router 1d must determine towards which gateway it should forward packets for destination x. Do we like AS2 or AS3 better? This decision is job of inter-as routing protocol 3c 3b AS3 3a x 1c 1a 1d 1b AS1 2a AS2 2c 2b Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

9 Internet inter-as routing: BGP Border Gateway Protocol (BGP): De facto standard for inter-as routing BGP provides each AS a means to: Advertise the existence of an IP prefix to other AS: This subnet is here Obtain subnet reachability information from neighbouring AS. Determine good routes to subnets based on reachability information and policy. Propagate reachability information to all AS-internal routers. Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

10 BGP basics Pairs of routers (BGP peers) exchange routing info over semi-permanent TCP connections: BGP sessions When AS2 advertises an IP prefix to AS1: AS2 promises it will forward IP packets towards that prefix AS2 can aggregate prefixes in its advertisement, for example: /24, /24, /23 into / :db8::/33, 2001:db8:8000::/33 into 2001:db8::/32 Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

11 How does BGP work? BGP is a path vector protocol BGP messages exchanged using TCP BGP Message types: OPEN: set up new BGP session, after TCP handshake NOTIFICATION: an error occurred in previous message tear down BGP session, close TCP connection KEEPALIVE: null data to prevent TCP timeout/auto-close; also used to acknowledge OPEN message UPDATE: Announcement: inform peer about new / changed route to some target Withdrawal: inform peer about non-reachability of a target Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

12 BGP updates Update (Announcement) message consists of Destinations (one or more IP prefix) AS Path (=Path vector) Next hop (=IP address of our router connecting to other AS) but update messages also contain a lot of further attributes: Local Preference: used to prefer one gateway over another Only communicated intra-as Origin: route learned via { intra-as inter-as other } Multi-Exit Discriminator, Community, It means BGP is not a pure path vector protocol, as it adds possibilities to the path vector idea. Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

13 ebgp and ibgp External BGP (ebgp): between routers in different ASes Internal BGP (ibgp): between routers in same AS Remember: In spite of intra-as routing protocol, all routers need to know about external destinations (default ibgp route or full tables) No different protocols - just slightly different configurations! 3c x 3a 3b AS3 1a AS1 1c 1d ebgp session ibgp session 1b 2a 2c AS2 2b Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

14 Distributing reachability info Using ebgp session between 3a and 1c, AS3 sends reachability info about prefix x to AS1. 1c can then use ibgp to distribute new prefix info to all routers in AS1 1b can then re-advertise new reachability info to AS2 over 1b-to-2a ebgp session When router learns of new prefix x, it creates a new entry for the prefix in its forwarding table. 3c x 3a 3b AS3 AS1 1a 1c 1d ebgp session ibgp session 1b 2a AS2 2c 2b Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

15 Path attributes & BGP routes Advertised prefix includes [many] BGP attributes prefix + attributes = route Most important attributes: AS-PATH: contains ASes through which prefix advertisement has passed: e.g., AS 67, AS 17, AS 7018 NEXT-HOP: indicates specific internal-as router to next-hop AS (may be multiple links from current AS to next-hop-as) When gateway router receives route advertisement, it uses an import policy to accept/decline the route More on this later Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

16 AS Numbers How do we express a BGP path? ASes identified by AS Numbers (short: ASN) Examples: Leibnitz-Rechenzentrum = AS12816 Deutsche Telekom = AS3320 TUM-I8-AS = AS56357 AT&T = AS7018, AS7132, AS2685, AS2686, AS2687 ASN assignment: similar to IP address space ASN space administered IANA Local registrars, e.g., RIPE NCC in Europe AS PATH specified by ASNs. The AS PATH does not contain IP addresses! Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

17 BGP update: Very simple example Type: Announcement new route existing route has changed Destination prefix: /24 Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

18 BGP update: Very simple example Type: Announcement new route existing route has changed Destination prefix: /24 AS Path: Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

19 BGP update: Very simple example Type: Announcement new route existing route has changed Destination prefix: /24 AS Path: Originator: The AS that owns /24 Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

20 BGP update: Very simple example Type: Announcement new route existing route has changed Destination prefix: /24 AS Path: Next Hop: Originator: The AS that owns /24 The router that connects the current AS to AS64496 Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

21 BGP update: Very simple example Type: Announcement new route existing route has changed Destination prefix: /24 AS Path: Next Hop: Originator: The AS that owns /24 The router that connects the current AS to AS64496 How the update travelled Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

22 BGP update: Very simple example Type: Announcement new route existing route has changed Destination prefix: /24 AS Path: Next Hop: Originator: The AS that owns /24 The router that connects the current AS to AS64496 How the update travelled How the IP packets will be forwarded (if this route gets chosen) Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

23 BGP route selection Router may learn about more than 1 route to some prefix Router must select the best one among these Elimination rules (simplified): 1. Longest prefix match 2. Local preference value attribute: policy decision 3. Shortest AS-PATH 4. Closest NEXT-HOP router: hot potato routing 5. Additional criteria It is possible to create Policies that may override the default behaviour, for instance to desconsider the longest prefix match, in other to use a cheaper link option. Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

24 Hot-potato routing Interaction between Inter-AS and Intra-AS routing If traffic is destined for other AS, get rid of it ASAP using Intra-AS routing to find shortest path to gateway Multiple transit points asymmetrical routing Asymmetrical paths are common on the Internet Host A AS 7018 Atlantic ocean AS 3320 Host B Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

25 ibgp scalability problem Every router in AS should know external routes Not only local neighbours, but also neighbours connected at other routers Many/all routers in AS have to run BGP sessions Need to select best inter-as routes Routers need to exchange routing information via ibgp O(n) BGP routers O(n²) ibgp sessions This does not scale! Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

26 Solution: BGP Route Reflectors (RR) Idea: One special router = Route Reflector (RR) Every ebgp router sends routes learned from ebgp via ibgp to RR RR collects routes, may do policing RR distributes routes to all other BGP routers in AS via ibgp Result: O(n) BGP routers, O(n) BGP sessions ebgp session ibgp session 1a AS1 1c 1d 1b Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

27 Terminology: Transit AS, stub AS, multi-homed AS Transit AS: Relays traffic between other Ases (Only about 15% of all ASes are Transit ASes.) Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

28 Terminology: Transit AS, stub AS, multi-homed AS Transit AS: Relays traffic between other Ases (Only about 15% of all ASes are Transit ASes.) Stub AS: Buys transit from only one other AS, but does not offer transit for other ASes Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

29 Terminology: Transit AS, stub AS, multi-homed AS Transit AS: Relays traffic between other Ases (Only about 15% of all ASes are Transit ASes.) Stub AS: Buys transit from only one other AS, but does not offer transit for other ASes Multi-homed AS: Buys transit from 2 other ASes, but does not offer transit for other ASes Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

30 Business relationships Internet = network of networks (ASes) Many thousands of ASes using BGP for routing between ASes Differences in economical power/importance Some ASes huge, intercontinental (AT&T, Cable&Wireless) Some ASes small, local (e.g., München: M-Net, SpaceNet) Small ASes customers of larger ASes: Transit traffic Smaller AS pays for connecting link and for data (buys transit) Business relationship: customer - provider Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

31 Business relationships Equally sized Cases Usually share cost for connecting links Business relationship = peering (no payments for traffic between those ASes) Peering Usually equal-size AS, but could be between big CDN and small ISP peers of a BGP connection (also may be customer or provider) peer-to-peer network Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

32 Business and policy routing Basic principle #1 (Routing) Prefer routes that are more cost-efficient If you have the choice, then routes via a customer are better than routes via a peer, which are better than routes via a provider. Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

33 Business and policy routing Basic principle #2 (Route announcement) Announce routes that produce income if used by others Others = customers Announce routes that reduce costs Route using peering Do not announce routes that incur financial loss as long as alternative paths exist be aware you may have bigger convergence time in case of failures announcing with lower priority could be an reasonable alternative Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

34 Business and policy routing A tells C all routes it uses to reach other ASes The more traffic comes from C, the more money A makes A provider customer C Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

35 Business and policy routing A and B tell C all routes they use to reach other ASes The more traffic flows from C to A, the more money A makes The more traffic flows from C to B, the more money B makes C will pick the one with the cheaper offer / better quality / A provider customer C B provider customer Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

36 Business and policy routing C tells A its own prefixes; C tells B its own prefixes C wants to be reachable from outside C does not tell A routes learned from/via B C does not tell B routes learned from/via A C does not want to pay money for traffic A C B A provider customer C B provider customer Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

37 Business and policy routing: Prefix Announcements C tells A its own prefixes C tells B its own prefixes but announces more specific prefix for one of the neighbours. Why? A expensive provider customer C B cheap provider customer Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

38 Business and policy routing: Prefix Announcements C tells A its own prefixes C tells B its own prefixes but announces more specific prefix for one of the neighbours. Why? Result: Route available for both peers, but longer prefix means more attractive path is preferred Technique may be used for load balancing A expensive provider customer C B cheap provider customer Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

39 Prefix Announcements Announce the aggregated prefix for all peers: If connection to one peer is lost, connection to Internet is maintained Example: 2001:db8::/32 is announced for all peers Announce more specific prefix for the preferred peer: This peer will be preferred when receiving traffic Example: Announce for the cheaper peer more specific prefix: 2001:db8:0000::/33 and 2001:db8:8000::/33 Announce for the other peers the aggregated prefix: 2001:db8::/32 Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

40 Prefix Announcements - Load Balancing Announce the aggregated prefix for all peers: If connection to one peer is lost, connection to Internet is maintained Consider the IPs in your network are equally distributed in the available address space. Announce specific prefixes in the desired proportion: Example: You want 1/4 from AS A and 3/4 from AS B Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

41 Prefix Announcements - Load Balancing Announce the aggregated prefix for all peers: If connection to one peer is lost, connection to Internet is maintained Consider the IPs in your network are equally distributed in the available address space. Announce specific prefixes in the desired proportion: Example: You want 1/4 from AS A and 3/4 from AS B Announce for AS A: Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

42 Prefix Announcements - Load Balancing Announce the aggregated prefix for all peers: If connection to one peer is lost, connection to Internet is maintained Consider the IPs in your network are equally distributed in the available address space. Announce specific prefixes in the desired proportion: Example: You want 1/4 from AS A and 3/4 from AS B Announce for AS A: 2001:db8:0000::/34 and 2001:db8::/32 Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

43 Prefix Announcements - Load Balancing Announce the aggregated prefix for all peers: If connection to one peer is lost, connection to Internet is maintained Consider the IPs in your network are equally distributed in the available address space. Announce specific prefixes in the desired proportion: Example: You want 1/4 from AS A and 3/4 from AS B Announce for AS A: 2001:db8:0000::/34 and 2001:db8::/32 Announce for AS B: Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

44 Prefix Announcements - Load Balancing Announce the aggregated prefix for all peers: If connection to one peer is lost, connection to Internet is maintained Consider the IPs in your network are equally distributed in the available address space. Announce specific prefixes in the desired proportion: Example: You want 1/4 from AS A and 3/4 from AS B Announce for AS A: 2001:db8:0000::/34 and 2001:db8::/32 Announce for AS B: 2001:db8:4000::/34, 2001:db8:8000:/33 and 2001:db8::/32 Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

45 Prefix Announcements - Load Balancing Announce the aggregated prefix for all peers: If connection to one peer is lost, connection to Internet is maintained Consider the IPs in your network are equally distributed in the available address space. Announce specific prefixes in the desired proportion: Example: You want 1/4 from AS A and 3/4 from AS B Announce for AS A: 2001:db8:0000::/34 and 2001:db8::/32 Announce for AS B: 2001:db8:4000::/34, 2001:db8:8000:/33 and 2001:db8::/32 This division may be used for other reasons, for example, business customers are announced for the expensive provider and residential customers in the cheap provider. Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

46 Prefix Announcements - Load Balancing Announce the aggregated prefix for all peers: If connection to one peer is lost, connection to Internet is maintained Consider the IPs in your network are equally distributed in the available address space. Announce specific prefixes in the desired proportion: Example: You want 1/4 from AS A and 3/4 from AS B Announce for AS A: 2001:db8:0000::/34 and 2001:db8::/32 Announce for AS B: 2001:db8:4000::/34, 2001:db8:8000:/33 and 2001:db8::/32 This division may be used for other reasons, for example, business customers are announced for the expensive provider and residential customers in the cheap provider. Announcement of unnecessary prefixes is bad for the whole Internet, think before using this solution. Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

47 Business and policy routing: AS path prepending C tells A its own prefixes C may tell B its own prefixes but inserts C multiple times into AS path. Why? A cheap provider customer C B expensive provider customer Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

48 Business and policy routing: AS path prepending C tells A its own prefixes C may tell B its own prefixes but inserts C multiple times into AS path. Why? Result: Route available, but longer path = less attractive Technique is called AS path prepending A cheap provider customer C B expensive provider customer Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

49 AS path prepending The same ASN subsequently within an AS path does not constitute a loop Recall the elimination rule for selecting from multiple path alternatives Prefer the shortest AS path is rule 3 Only ignored if Local Pref value is set AS path prepending makes a route less attractive will then only be used when there is no alternative Can be used, e.g., for a slow or expensive backup link How many times to repeat the AS number? Usually just 1 or 2 repetitions More than 5 is useless Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

50 Business and policy routing What should C announce to A? A provider customer C provider customer D Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

51 Business and policy routing What should C announce to A? C tells A about its own prefixes A provider customer C provider customer D Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

52 Business and policy routing What should C announce to A? C tells A about its own prefixes C tells A about its route to D s prefixes: loses money to A, but gains money from D A provider customer C provider customer D Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

53 Business and policy routing What should C announce to E? peering C provider customer D E Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

54 Business and policy routing What should C announce to E? C tells peering partner E about its own prefixes and route to D: no cost on link to E, but gains money from D peering C provider customer D E Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

55 Business and policy routing Which route to p should C select? provider B customer peering C E p Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

56 Business and policy routing Which route to p should C select? B tells C about route to prefix p (lose money) E tells C about route to prefix p (± 0) C prefers route via E provider B customer peering C E p Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

57 Business and policy routing What should C announce here? F peering peering C provider customer E Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS D

58 Business and policy routing What should C announce here? C announces to F and E: its own prefixes and D s routes F peering peering C provider customer E Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS D

59 Business and policy routing What should C announce here? C announces to F and E: its own prefixes and D s routes C does not announce to E: routes going via F Otherwise: E could send traffic towards F but wouldn t pay anything, F wouldn t pay either, and C s network gets loaded with additional traffic F peering peering C provider customer E Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS D

60 Business and policy routing What should C announce here? C announces to F and E: its own prefixes and D s routes C does not announce to E: routes going via F Otherwise: E could send traffic towards F but wouldn t pay anything, F wouldn t pay either, and C s network gets loaded with additional traffic C does not announce to F: routes going via E Same reason F peering peering C provider customer E Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS D

61 Policy routing: Valley-free routing (idealised!) Results: Packets always travel 1. upstream: sequence of C P links (possibly length = 0) 2. then possibly across one peering link 3. then downstream: sequence of P C links (possibly length = 0) provider customer peering provider customer provider provider customer customer Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

62 Tier-1, Tier-2, Tier-3 etc. Tier-1/DFZ = only peerings, no providers Tier-2 = only peerings and one or more Tier-1 providers Tier-3 = at least one Tier-2 as a provider Tier-n = at least one Tier-(n-1) provider defined recursively n 4: Rare in Western Europe, North America, East Asia Tier-1.5 = almost a Tier-1 but pays money for some links Example: Deutsche Telekom used to pay money to Sprint, but is now Tier-1 Marketing purposes: Tier-1 sounds better DFZ: Default Free Zone, ASes here can t use a default route to reach a desired destination. Tier-3 and smaller with only one provider or a preferred provider may use a default route (send all my traffic to this provider), instead of learning the full BGP table Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

63 BGP Table Size IPv4: 700,000 IPv6: 40,000 (Source: on May 2017) Source: on May 2017 Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

64 Siblings Not everything is provider/customer or peering Sibling = mutual transit agreement Provide connectivity to the rest of the Internet for each other very extensive peering Examples Two small ASes close to each other that cannot afford additional Internet services Merging two companies Merging two ASes into one = difficult, Keeping two ASes and exchaning everything for free = easier Example: AT&T has five different AS numbers (7018, 7132, 2685, 2686, 2687) Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

65 Where to peer (Here: Peering = having a BGP relationship) A. Private peering The obvious solution: Let s have a cable from your server room to our server room B. At public peering locations (Internet Exchange Point, IX, IXP) A room full of switches that many providers connect to Configure VLAN connections in switch, instead of having to put in O(n²) separate wires Examples: DE-CIX, Frankfurt (purportedly largest in world, peak of 5.6 Tbps) AMS-IX, Amsterdam (peak of 5.5 Tbps) LINX, London MSK-IX, Moscow IX-BR, São Paulo Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

66 Summary How the Internet works? Default Free Zone Source: Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS

67 Questions? Edwin Cordeiro How the Internet works? The Border Gateway Protocol (BGP) ilab 2 Lecture SS