Cisco - Large Meshed IP Backbone Architecture - Session 1501

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© 1999, Cisco Systems, Inc.

Large Meshed IP Backbone Architecture Session 1501

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Agenda

• Why? What? Who? • Network Topologies • Addressing • Routing • Other Stuff 1501 1120_06F9_c2

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Who Are You?

• Internet Service Provider/ telephone company • Very large corporation • Government • Aspiring one of above • Principles also apply to smaller nets 1501 1120_06F9_c2

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Definitions • PoP—Point of Presence vPoP—Virtual PoP (backhauled access point) Hub—Major ISP presence; large central PoP

• Routing—Building a forwarding table • Forwarding—Switching packets between interfaces • Transit—Carrying traffic across a network, perhaps for a fee • Peering—Exchanging routing information and traffic • Default—A next hop indication when no explicit match is in the forwarding table 1501 1120_06F9_c2

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Definitions • Neighbors—AS’s which directly exchange routing information • Announce—Send routing information to a neighbour • Accept—Receive and use routing information sent by a neighbour • Originate—Insert routing information into external announcements • Peers—Routers in neighbouring AS’s or within one AS which exchange routing and policy information 1501 1120_06F9_c2

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Autonomous System (AS) AS 100

• Collection of networks with same routing policy • Single routing protocol • Usually under single ownership, trust and administrative control 1501 1120_06F9_c2

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Customers • Define “us” or “them” • A domain (us.com, them.gov)? • An autonomous system? • Administrative boundaries and controls

Them 1501 1120_06F9_c2

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Us 8

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Customers (Cont.) • Easy for ISP—The people who give you money • Harder for very large organizations (corporations, governments, etc.) Subsidiaries Geographic boundaries Departments 1501 1120_06F9_c2

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Basic Scaling Concepts

Regional Regional Network NetworkB B

• Hierarchy • Discipline • Information reduction • Consistency

NAP NAP

Japan

Europe

NAP

Milnet Milnet Backbone Backbone 22

Backbone Backbone 33

Fed Fed Nets Nets FIX-East FIX-East

FIX-West FIX-West

Australia

• Planning

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NAP NAP

Backbone Backbone 11

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CIX CIX

Regional Regional Network NetworkA A

MAF(E/+)-East MAF(E/+)-East

Backbone Backbone 4, 4, 5, 5, N N

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Scaling Sizes • First order: 1,000 sites • Second order: 10,000 sites 10 x 1,000 site networks

• Third order: 100,000 sites 100 x 1,000 site networks

• “Fractal Design” Self-repeating patterns 1501 1120_06F9_c2

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Topology

Backbone

• Backbone • Distribution • Access

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Distribution

Access

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Topology • Core routers—High speed trunk connections • Distribution routers—High port density • Access routers—Connections to others • Some functions may be collapsed into a single box • Some functions can be handled by switches (but not all at once) 1501 1120_06F9_c2

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Backbone • 10 to 40-50 Locations Scaling Routing Manageability

• Simple One routing protocol One media No packet manipulation 1501 1120_06F9_c2

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Backbone (Cont.) • Fast Interconnect only No customer access

• Highly reliable locations Power Staffing Physical Hardening 1501 1120_06F9_c2

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Backbone (Cont.) • Locations Data centers Telephone central offices/PoPs

• Should follow physical topology Optical fiber plant ATM switches Circuit pricing issues 1501 1120_06F9_c2

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Backbone

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Layer 2 Switched vs. Layer 3 Switched

• ATM or Frame Relay

• SONET

Finer control granularity

Less overhead

Circuit oriented

Layer 3 based control

N squared issue

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Network Topologies • Switched backbone • Frame Relay or ATM Switches in the core Surrounded by routers

• More complex routing and debugging • Traffic management 1501 1120_06F9_c2

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Network Topologies

• Routed backbone • HDLC or PPP links between routers • Easier routing configuration and debugging

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POSIP vs ATM

• Pure IP networks • Efficient link usage • Well known routing protocols for best effort traffic

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• Multiservice networks Frame Relay Circuit emulation

• Very granular QoS

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SONET SRP-LC

ADM

SRP-LC O-Rx I-Tx I-Rx O-Tx

ADM

O-Tx I-Rx I-Tx O-Rx

SONET/SDH Network

ADM

O-Tx I-Rx I-Tx O-Rx

SRP-LC

• Clock derived from SONET/SDH network • Looped or line timed 1501 1120_06F9_c2

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WDM or Direct to Fiber SRP-LC O-Rx I-Tx

WDM

WDM

~ ~

~ ~

I-Rx O-Tx 20ppm

O-Tx I-Rx

SRP-LC 20ppm

I-Tx O-Rx Direct to Fiber or through Regen

• Clock derived from internal oscillator • No need for central clock source • No complex clocking requirements • Although it is a ring topology clocking is pt to pt • Similar to doing POS back to back 1501 1120_06F9_c2

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Layer 2 Switched

• ATM Often less expensive (for noncarrier) Easy city-pair traffic engineering

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Layer 2 Switched • Full mesh of circuits

CHI

• Separates circuit capacity • A fully meshed ISP backbone is common mistake of single Layer 2 thinking • Full mesh ISP backbones limit scalability as they grow in size 1501 1120_06F9_c2

SFO BOS

LAX

NYC

DEN ATL DFW

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Layer 2 Switched CHI

• n squared hard to manage • If buying bandwidth, can add to hot city pair • n(n-1) peers

SFO BOS

LAX

NYC

DEN ATL

• No hierarchy DFW

• Limited scalability 1501 1120_06F9_c2

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State of the Internet POP 5,000

2 x OC48 4,000

City-Pair Bandwidth Requirements

3,000

Mbps

OC48 Tier 1 ISP

2,000

2 x OC12 1,000 OC12

Tier 2 ISP

500 0

Jan ’96 1501 1120_06F9_c2

Jan ’97

Jan ’98

Jan ’99

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Layer 3—IP IP • Reducing unnecessary layers of equipment significantly Lowers equipment cost

ATM SONET/SDH

Lowers operational cost

WDM

Simplifies architecture

FIBER 1501 1120_06F9_c2

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No Switched Layer 2 CHI SFO BOS

• Direct fiber connectivity

LAX

NYC

DEN ATL DFW

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Tiered Network Design Other Regions

Other Regions Core Other Regions

Distribution Layer

Access Layer 1501 1120_06F9_c2

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Distribution Backbone

Distribution Networks

• Mesh of meshes • Take advantage of tariffs and regional infrastructure 1501 1120_06F9_c2

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POP Intraconnect

FDDI 100Mbps

POS N x 155

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SRP 2 x 622Mbps

Fast/Gig Ethernet 100/1000Mbps

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Distributed POP—Metro Area Backbone

MAN

Access Ring

Access Ring

Access Ring

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Frame Relay Example

Backbone PoP

Peer Networks

POP Intraconnect

Location Access

Residential Access Commercial Frame Relay Provider 1501 1120_06F9_c2

Commercial Bandwidth Provider

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Access • Last piece of equipment you control Aggregation equipment in POP Customer Premise Equipment (CPE)

• Define demarcation point WAN link to customer? LAN port on router at customer? See Session #2xx Access Technologies 1501 1120_06F9_c2

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Reliability vs. Cost Tradeoffs • Within backbone • Distribution to access • WAN links • Access equipment • Service level agreements • Users impacted X costs/user 1501 1120_06F9_c2

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Point of Impact

Backbone

Peer Networks

PoP Location Access

Residential Access

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PoP Design • Triple Layered POP Redundancy Two connection to the backbone from any border router Two border routers, load balanced with one able to take the full load Two POP interconnect devices and/or a physical failover medium ( FE/GE, POS, DTP) 1501 1120_06F9_c2

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Backbone

Border

Intra-POP Interconnect

POP Intraconnect

Access

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Addressing

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Addressing

• Registered/nonregistered • Customer addresses • Infrastructure addresses • Aggregating addresses

See Session #806 “DNS, DHCP and IP Address Management” 1501 1120_06F9_c2

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Not Registered (Private) • RFC 1918 10.0.0.0

10.255.255.255

172.16.0.0

172.31.255.255

192.68.0.0

192.68.255.255

• Not Internet routed • Technically possible to use for ISP Infrastructure—Not recommended 1501 1120_06F9_c2

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Registered Space • Harder to get huge blocks • Expected with ISPs Traceroute—Public debugging help

• ARIN/APNIC/RIPE • Upstream/transit ISP offers some of their addressing Can lock you in 1501 1120_06F9_c2

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Separate Infrastructure and Customer Addressing

• Eases administration of policies • Security and management • Routing management • Don’t share network 10!

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Customer vs. Infrastructure Customer 1 10.0.0.0

Customer 2 172.16.0.0

Customer 3 192.192.192.0 You 10.0.0.0? 172.16.0.0? W.X.Y.Z? ?

Customer 4 10.0.0.0

See Session #1306 “Expanding Connectivity With NAT” 1501 1120_06F9_c2

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Addresses Not Scaling 195.54.212.16 195.54.212.17 195.54.212.18 195.54.212.19 195.54.212.24 195.54.212.25 195.54.212.26 195.54.212.27 195.54.212.33 195.54.212.34

lint.abc.com ping.abc.com biff.abc.com hill.abc.com ftp.abc.com mail.abc.com wish.abc.com dirt.abc.com note.abc.com rex.abc.com

195.54.212.14 195.54.212.15 195.54.212.20 195.54.212.21 195.54.212.22 195.54.212.23 195.54.212.28 195.54.212.29 195.54.212.30 195.54.212.31

jill.abc.com goof.abc.com over.abc.com retro.abc.com mike.abc.com lazy.abc.com wiz.abc.com sas.abc.com chez.abc.com pez.abc.com

• Too many routes • Wasted address space 1501 1120_06F9_c2

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Aggregating Addresses

• Prefixes in backbone 60,000 Entries in Internet on 6/2/99 http://www.employees.org/~tbates/

• Scaling method for routing

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What Is Route Summarization? 172.16.25.0/24

172.16.26.0/24

I Can Route to the 172.16.0.0/16 Network

A

172.16.27.0/24

Routing Table 172.16.25.0/24 172.16.26.0/24 172.16.27.0/24

Routing Table 172.16.0.0/16

• Routing protocols can summarize addresses of several networks into one address 1501 1120_06F9_c2

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Route Aggregation Old Method:

202.14.64.0 202.14.65.0 202.14.66.0

32 Routes

202.14.96.0

New Method:

202.14.64.0/19

1 Route

• 131.108.0.0 /16 versus 255.255.0.0 • Summarizable blocks of subnets 1501 1120_06F9_c2

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Addressing and ISPs ISP #1 Customer Customer #1 #1 202.14.64.0/19 202.14.64.0/19

Customer Customer #2 #2 202.14.8.0/21 202.14.8.0/21

Customer Customer #3 #3 202.14.2.0/23 202.14.2.0/23

202.14.0.0/16

ISP #2

ISP #3

• Smaller routes aggregated within ISP #1 1501 1120_06F9_c2

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Route Scaleability

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Effects of CIDR in the Internet

Before CIDR After CIDR

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Minimum Routing Table Entries Other Regions

Other Regions Backbone Other Regions

Distribution Layer

Could Be as Few as TWO Routing Table Entries from Region to Backbone

Access Layer 1501 1120_06F9_c2

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Routing

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Routing

• Interior Gateway Protocols (IGPs) Infrastructure routes

• Exterior Routing Protocol (BGP) Customer routes, Internet routes

See Session #301 “Introduction to Routing” 1501 1120_06F9_c2

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Interior vs. Exterior Routing Protocols • Interior

• Exterior

Automatic discovery

Specifically configured peers

Generally trust your IGP information

Connecting with outside networks

Routes go to all IGP routers

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Set administrative boundaries

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Hierarchy of Routing Protocols Other ISPs BGP4

BGP4/OSPF

BGP4 Local NAP FDDI

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BGP4/Static

Customers

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What Is an IGP? • Interior gateway protocol • Within an autonomous system • Carries information about internal prefixes • Examples—OSPF or ISIS or EIGRP • Classless (VLSM) 1501 1120_06F9_c2

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Enhanced IGRP • Extremely fast convergence • Discontiguous subnets • Arbitrary route summarization • Supports prefix and host routing

• Best of DV and LS • Low overhead • Guaranteed loop free • Reliable, incremental update based • Does not enforce discipline!

See Session #307 “Deploying (E)IGRP)” 1501 1120_06F9_c2

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OSPF • Open Shortest Path First • Link state or SPF technology • Developed by OSPF working group of IETF (RFC 1253) • Designed expressly for TCP/IP Internet environment 1501 1120_06F9_c2

• Fast convergence • Variable-length subnet masks • Discontiguous subnets • No periodic updates • Route authentication

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OSPF Areas and Rules

• Backbone area (0) must be present Area 2

Area 3

• All other areas must have connection to backbone • Backbone must be contiguous

Area 0

Area 4 Area 1

• Do not partition area (0)

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Scalable OSPF Network Design

• Area hierarchy • Stub areas • Addressing • Route summarisation

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OSPF Rules of Thumb Backbone Area 0 Area 1

Area 3

Area 2

• Max of 3 areas per router • Max of 25, 50, or 100 routers per area • Use default routing and stub areas wherever possible • If links are unstable, reduce the number of routers per area 1501 1120_06F9_c2

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Inter-Area Route Summarisation • Prefix or all subnets • Prefix or all networks

R2

• ‘Area range’ command With Summarisation

Network 1

Next Hop R1

Without Network Summarisation 1.A 1.B 1.C

Next Hop R1 R1 R1

FDDI Dual Ring

Backbone Area 0

R1 (ABR) Area 1

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1.A

1.B

1.C

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When to Use OSPF

• Large hierarchical networks • Can scale very large • Topology restrictions

See Session #308 “Deploying OSPF/ISIS” 1501 1120_06F9_c2

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IS-IS • IS = Intermediate System • Dual IS-IS • Integrated IS-IS • Metric is 6 bits wide (1-63)* • All interfaces default to 10 1501 1120_06F9_c2

• ISO 10589 • Two types of areas: Level-1 other areas Level-2 backbone

• Default for each level • Much like OSPF • Scales well

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Configuring Aggregation

• Three ways to configure route aggregation Redistribute static Network command Aggregate-address command

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Not Summarised: Specific Links • Specific link LSA advertised out • Link state changes propagate out

External Links ASBR

Backbone Area #0

1.A 1.B 1.C 1.D

2.A 2.B 2.C

1.B

3.B

1.A Token Ring

Token Ring

3.A 3.B 3.C 3.D

Token Ring

2.B

Token Ring

Token Ring

1.D

1.C

3.A

3.C

3.D

2.A

Token Ring

2.C 1501 1120_06F9_c2

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Not Summarised: Specific Links • Only summary LSA advertised in/out • Link state changes do not propagate

External Links ASBR

Backbone Area #0

1

3

2 1.B

3.B

1.A

3.A

2.B 1.C

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1.D

2.A

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3.C

3.D

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What Is an EGP? • Exterior Gateway Protocol • Used to convey routing information between autonomous systems • De-coupled from the IGP • Current EGP is border gateway protocol See Session #309 “Deploying BGP” 1501 1120_06F9_c2

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Why Do We Need an EGP? • Scaling to large network Hierarchy Limit scope of failure

• Policy Control reachability to prefixes Merge separate organizations Connect multiple IGPs 1501 1120_06F9_c2

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Border Gateway Protocol (BGP)

• BGP version 4 is the current de facto external routing protocol in the Internet • BGP-4 is required for CIDR

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Autonomous System Number (ASN) • Organizational networks within a single domain are known as Autonomous Systems (AS) ASNs are allocated by the APNIC, ARIN, or RIPE-NCC Must have an ASN to run BGP RFC 2050 defines the latest policies for ASN allocations 1501 1120_06F9_c2

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Policy Drives BGP Requirements

AS 200 BGP

AS 100

BGP

AS 400

BGP

AS 300

• Policy for AS 100: Always use AS 300 path to reach AS 400 1501 1120_06F9_c2

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Border Gateways • How it affects your traffic patterns

NAP

ISP #3 NAP

ISP #2 ISP #1

Same City

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BGP

• How does BGP work? Internal BGP Route reflectors External BGP

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Internal BGP (IBGP) Peering AS 100 D A

B

E

• • • • 1501 1120_06F9_c2

BGP peer within the same AS Not required to be directly connected IBGP neighbors should be fully meshed Few BGP speakers in corporate network

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IBGP Core Architecture IGP 5

IGP 5

IGP 6

IGP 6 AS 64530

IGP 7

IGP 7

IGP 8

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IGP 8

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Scaling iBGP mesh A

AS 100 B

C

• Need to avoid routing information loop • Solution should not change the current behaviour • Two solutions: Route reflectors—simpler to deploy and run Confederation—difficult 1501 1120_06F9_c2

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Route Reflector: Principle • Router Reflector allows for a BGP hub (star) configuration

Reflector

A

AS 100 B

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C

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Route Reflector: Benefits • Solves iBGP mesh problem • Packet forwarding is not affected • Normal BGP speakers co-exist • Multiple reflectors for redundancy • Easy migration • Multiple levels of route reflectors 1501 1120_06F9_c2

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External BGP (EBGP) Peering

A

AS 100

AS 101 C B

• Between BGP speakers in different AS • Should be directly connected • Don’t run an IGP between EBGP peers 1501 1120_06F9_c2

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Routing To Customers

• Normal—static route Redistribute to BGP

• eBGP with them • DO NOT SHARE YOUR IGP!

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Explicit vs. Default Routing • Default: Simple, cheap (cycles, memory, and bandwidth) Low granularity (metric games)

• Explicit More overhead, more complex, and higher cost High granularity 1501 1120_06F9_c2

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Connecting to the Internet • Full routes option Greatest flexibility Resource intensive

• Default Simple Less granular 1501 1120_06F9_c2

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Other Scaling Techniques

• Route flap dampening Tracks unreliable BGP routes More unreliable is carried less

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Route Filtering Network X

• Selectively announce routes, per neighbor Hide part of the topology/connectivity

• Do not believe your customers routes • Enable addresses block by block 1501 1120_06F9_c2

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Advertise B and Y

Network A

Advertise B and X

Network B

Network Y 86

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Redistribution

• Static -> BGP okay • IGP -> BGP rarely • Do not: IGP -> IGP BGP -> IGP 1501 1120_06F9_c2

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The Other Stuff Bandwidth, Security, Team, and Testing 1501 1120_06F9_c2

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Bandwidth • Levels of service Different services? Best effort internet vs. packet telephony QoS/priorities/traffic engineering

• Oversubscription ratios See Session #310 “Deploying Traffic Management (QoS) Technology” 1501 1120_06F9_c2

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Security • Do not trust CPE equipment that is not under your complete (including physical) control • Securing infrastructure • Other security See Session #311 “Deploying Security Technology” 1501 1120_06F9_c2

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Secure Routing Route Authentication Configure: Key and Hash Function

Campus Signs Route Updates

Verifies Signature Signature

Route Updates

• Certifies authenticity of neighbor and integrity of route updates 1501 1120_06F9_c2

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Authentication, Authorization and Accounting (AAA)

• Verifies identity = Who are you? • Authorization = Configures integrity What are you permitted to do? • Accounting = Assists with audit What did you do?

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Centralized Security Servers

• Includes centralized security database with username, password and authorization information • For use with a variety of authentication protocols including TACACS+, RADIUS, one-time password mechanisms 1501 1120_06F9_c2

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Other Infrastructure Security

• SMNP—limit • Telnet encryption • TFTP servers

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Access/Edge Functions • NAT #1306 “Expanding Connectivity With NAT”

• Content caching #1302 “Update on Web Caching Technology”

• Voice #402 “Introduction to Voice Over IP and Other Integrated Services” 1501 1120_06F9_c2

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Web Caching Service Provider Backbone

POPs Exit to the Backbone Intra-POP Interconnect

Distribution: Service Node/ Customer Access

Bandwidth Mismatches—Broadband Customer Access 1501 1120_06F9_c2

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Managing the Network • Document (for real) • Plan ahead #609 “Introduction to Capacity Planning and Performance Management”

• Know your limits #601, 602, 603 “Device Architecture and Performance”

• Limit centralized polling (SNMP, ping) See Session #8xx “Network Management Technologies” 1501 1120_06F9_c2

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Scaling Operations

• Few operators allowed to configure backbone infrastructure • Define clear processes/automate customer provisioning • Documentation, simplicity, and repetition 1501 1120_06F9_c2

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Empowering People • People—not bandwidth, content, or applications—are THE most critical factor • Raise skills

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Labs and Testing • Cisco IOS ™ is the OS for your intranet • Test new releases with existing applications, like a new server OS release • Test new applications on a test network before deployment, like a test server • An ounce of preparation is worth… 1501 1120_06F9_c2

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Please Complete Your Evaluation Form Session 1501

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