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Exterior Routing 201

This article explores the quirks, definitions, and issues of ISP external routing and infrastructure, including POPs, router requirements, and playing in the club. It also discusses the importance of path selection and improving capacity and availability for ISPs.

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Exterior Routing 201

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  1. Exterior Routing 201 Howard C. Berkowitz hberkowi@nortelnetworks.com hcb@clark.net (703)998-5819 ESN 451-5819

  2. Agenda • What's the problem? • Formal and informal clue • ISP service offerings • Quirks, Defnitions, and Issues • ISP External Scenarios • POP and other infrastructure • Router requirements • Playing in the Club • Turning it On If there's time...full employment for consultants: path selection

  3. What is the Problem to be Solved?

  4. Good little boys and girls read RFC1771 and live happily ever after

  5. Noah. • Noah. • (yawn) MMMmmmmhp? • Noah. • Yeahh? • Build an ISP.

  6. Entry Basic Internet Access Hosting Availability and QoS Dealing with specialized access providers (DSL, CATV, etc.) Dealing with content providers Voice services? Improvement for Users Improving capacity Improving availability Adding services Perceptions of end-to-end SLA ISPs Facing End User

  7. Before the Animals Downlinks Uplinks Management Routers Facilities User Hosts HVAC Staff

  8. Load the Ark From Virtual Hosts Traffic Policies Policies Traffic Traffic From Upstreams From Downstreams Traffic AAA From Users

  9. Quirks, Definitions and Issues

  10. I said "peer," not "peer" • Peer relationship 1 • Basic BGP session • Peer relationship 2 • Mulual benefit customers reach one another • No monetary exchange • Each advertises customer routes • Transit Provider relationship • Customer pays for service • Full routes available to customer

  11. (C) O'Leary Museum and Library Association Ltd. Inc.

  12. Paths are not optimized end-to-end Paths are optimized for each AS Closest Exit RoutingHot potato dest src

  13. No guarantee that traffic leaving your AS at one point Will return at the same point Remember Each AS in both directions makes decisions on its information Asymmetrical Routing

  14. ISP Scenarios

  15. ISP #2 ISP #1 /16 /16 Core /18 /18 /18 8x/23 POP1 POP2 POP3 Hosted Servers Internal Servers Basic Internet Access ISP • From customers • Few # public routes • ??? VPN To 70-90% of customers Default route To 5-10% of customers Partial routes To 10% of customers Full routes

  16. Big ISP 1 Big ISP 2 Bilateral Peering eBGP Relationship Exchange of customer routes only Some aggregation No infrastructure routes Highest bandwidth requirement "Tier 1 Provider" Does not buy transit service from anyone Has default-free routers Gets all routes from bilateral/multilateral peering Total RIB size of 1.3-1.5 * DefaultFreeZone (D)

  17. Provider L3 Path Determination Firewall, etc. L7 Distribution L4 distribution GE ports 10/100 Server Server Server Large Content Provider • Sometimes bandwidth limited • Provider may be default free • Often high touch processing limited • Possible SLA and VPN agreements May participate in content distribution, caching

  18. ISP 1 ISP 4 Layer 2 Fabric ISP 2 ISP 5 ISP 3 ISP 6 Route Server Multilateral Peering eBGP Relationships Depending on exchange rules Exchange of customer routes only Most common case Some aggregation No infrastructure routes Some ISPs buy transit services Can receive full routes Private peerings Largest carriers tend to avoid due to congestion ISPs can peer with route server rather than a mesh of ISPs May be done to reduce BGP peers Or simply for statistics collection

  19. Entry Who's in charge? Connectivity Facilities Allow content providers? Allow end users? Peering model? Supplementary services? Improvements ISP 1 ISP 4 Layer 2? 3? Fabric ISP 2 ISP 5 ISP 3 ISP 6 Route Server Special Case: Local Exchanges

  20. POP and Other Internal Design

  21. Typical Basic POP Implementation Gigabit Ethernet Router Fabric Frame Interfaces ATM Interfaces 32x/30 /18 /18 LAN Switch Frame DS3 Full DS3 ISP Core Router 1 ISP Core Router 2 2x/25 Customer Site Routers Customer Site Router Management Servers Access Server Dedicated Customers Dedicated Customers PSTN 25 per POP 1 per POP Dialup Customers 450 users per POP

  22. Transit Provider POP, Intra-POP Design Alternatives 1. POP is a route reflector cluster Core is higher-level cluster 2. Each POP is a private or public AS Full mesh iBGP or route reflectors inside POP Confederation between POPs 3. IGP within POP Controlled redistribution inside POP to BGP Prefer intra-POP of same metric POP Router POP Router Access Router Access Router

  23. POP Confederations Public AS POP AS65000 POP AS65111 POP AS65222

  24. POP Reflectors Public AS POP AS65000 POP AS65111 POP AS65222

  25. Open Access/Specialized Access ISP 1 Subscribers Tunnel Server ISP 2 Layer 1/2 Fabric ISP 3 Internal Routed Network Content Servers

  26. PPPoE or GRE Tunneled Addressing Voice Provider 1 Access Gateway Internal Routing & Switching CLE Data Provider 1 Enterprise VPN NAS DHCP DNS CLE Data Provider 2 CLE Access OAM address space ISP address space L2TP, Differv High VoIP Data 1 Data 2 L2TP, Differv High VPN

  27. Router Requirements Big part of the solution...but not all.

  28. Low Medium Medium Low Low Low End to End High High High Medium High High EtE & PHB Medium High Medium Low PHB Medium Low Routing Paradigms Enterprise Edge Core Number of Interfaces Number of Routes Forwarding Bandwidth Hello Processing Policy Analysis QoS Awareness L4/7 Processing

  29. Observations on Routing Table Size • Global default-free table continues to grow exponentially • 96509 routes as of Tony Bates' CIDR report 2/11/2001 • Let the default routing table size be D • Large provider often has 1.3 to 1.5 D active routes • additional routes are more-specific customer & internal • may also have substantial numbers of inactive routes

  30. Growth in Global Routing Table Size 736K 368K 184K Sep 01 Sep 02 Sep 03 Sep 04 85K public

  31. Growth in Typical Tier 1 Routing Table Size(external + customer, not infrastructure) 1104 552 276 Sep 01 Sep 02 Sep 03 Sep 04 85K public 42K internal

  32. Observation: More than Routes • Customer routes • Paths per route • Route validity

  33. Convergence • Global routing system • Intra-AS • Single Router

  34. Initialization Time to add new route Time to add better route Time to withdraw route Time to withdraw and replace route Parameters Matrix: number of peers versus Routes advertised Routes accepted Performance Modifiers Route filtering Route flapping Packet vs. route filtering Single Router Convergence draft-berkowitz-bgpcon-0x.txt

  35. Distinguish among cases • Failover of link or router between customer and provider • Rerouting to intranet/adjacent provider resources • Rerouting to arbitrary internet destnation More multihoming in next tutorial

  36. S-T-R-E-T-C-H

  37. Joining the Club

  38. Specify Policy Route Track Service More than Just Addresses, Protocol... Address Registry Route Registry Allocate ISP with Prefixes Routing System Directories Routing Registry Customer Maintainer objects Configs SWIP NAT Route objects DNS Reverse DNS AS objects Hosts

  39. Complexity • BGP itself is fairly simple • Additional attributes it carries are more complex • Policy actions taken inside router (BGP sender or receiver) far more complex than the protocol itself

  40. "BGP Transmits Policies" Wrong!

  41. Operational Relationships 1Addresses and Delegation Address authority Reverse DNS DNS Address delegation Prefixes Hosts

  42. Obtain routable address space • Apply to registry • RIPE, APNIC, ARIN • If immediate need for /19 or /20* • Obtain addresses from upstream ISP • If /19 or /20 cannot be justified • Registry needs • Network design • Justification for address space

  43. Origination vs. Advertising AS65000 AS65000 128.0.0.0/19 AS64444 192.0.0.0/16 AS 65000 192.0.0.0/16 AS64444 an AS65000 Customer 128.0.0.0/20 /23 POP Dialups /23 Internal /23 Customers /23 Customers /25 /25 /25 /25 32 * /30 /25 /25 32 * /28 /24 /24

  44. 128.0.0.0/20 /23 POP Dialups /23 Internal /23 Customers /23 Customers /25 /25 /25 /25 32 * /30 /25 /25 32 * /28 /24 /24 Aggregating your Own Traffic AS65000 128.0.0.0/19 Suppress more specific routes unless required by multihoming

  45. Advertising with NO-EXPORT AS63333 64.0.0.0/12 Assigns 64.0.0.0/22 Assigns 64.0.4.0/22 AS62222 AS61111 Advertises 64.0.0.0/22 NO-EXPORT Advertises 64.0.4.0/22 NO-EXPORT 96.1.0.0/16 AS61000 96.1.0.0/16

  46. Aggregation is better than Aggravation • Blackhole routes for your blocks • Avoid more-specifics • Use NO-EXPORT when controlling load to upstream • Encourage customers to aggregate • Proxy aggregation hard to administer • Understand which blocks you can advertise • And do ingress/egress filtering

  47. Preparing for Address Request (1) • Address requirements of services are you offering • Dynamic addressing • Dialup • Residential broadband • Private addressing • Enterprises homed only to you • Dialup/broadband not offering servers • Globally addressable

  48. Hosting Farm 1 Infrastructure Servers Hosting Farm 2 Core Router 2 Core Router 1 Prepare for Address Request (2) An ISP Topology Switch POP1 1 internal LAN POP2 1 internal LAN POP3 1 internal LAN POP4 1 internal LAN 100 Dial Ports 8 small LANs 1 med. LAN 100 Dial Ports 8 small LANs 1 med. LAN 100 Dial Ports 8 small LANs 1 med. LAN 100 Dial Ports 8 small LANs 1 med. LAN

  49. Establishing an AS (1)AS Number Request • In request to AS number registry • Administrative and technical contacts • Autonomous system name • Router description • Deployment schedule • Networks (by name) connected by the router(s) • Internet addresses of the routers

  50. Establishing an AS (2)Registering in Routing Registry • Minimum requirements • Maintainer object • AS object • Route object (s)

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