Implementing and maintaining an isp backbone
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Implementing and Maintaining an ISP Backbone. Kevin Butler. Tier 1 ISP Backbones. Comprise some of the world’s largest IP networks Tier 1 companies include Sprint, AT&T, PSINet

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Tier 1 isp backbones
Tier 1 ISP Backbones

  • Comprise some of the world’s largest IP networks

  • Tier 1 companies include Sprint, AT&T, PSINet

  • UUNET has the world’s largest IP data network, presence on four continents and future expansion into Latin and South America

Service level agreements
Service Level Agreements

  • SLAs are an important and prestigious tool in attracting and maintaining customers

  • Comprised of uptime guarantees and bounds on latency through various geographic regions

  • most ISPs currently have latency < 50ms across the US

Supporting the customer
Supporting the Customer

  • Quality and expertise of first-line customer support varies wildly between companies

  • depending on size, geographic location and company focus, some front-line support teams outsourced to third parties

  • some in-house high level support teams have skills equivalent or superior to NOCs

Network operations centres
Network Operations Centres

  • Generally the teams concerned with backbone maintenance and support

  • trend towards consolidation into “Super-NOCs” (eg. one for Americas, one for Europe)

  • specialisation within NOC for product support (eg. dial, VPN, backbone NOCs)

Noc tools
NOC Tools

  • NOCOL - Network Operations Centre On Line (freeware UNIX)

  • Mediahouse monitoring (mainly web)

  • Micromuse Netcool (now owned by Lucent) - used by MCI WorldCom, PSINet, BT

Dial access
Dial Access

  • Dial is a major selling point, especially with customers who travel a lot or are their own ISPs

  • connections made through an Ascend MAX TNT, which can support up to 720 concurrent callers

  • back-end is a DS-3 into a backbone router, routers advertised by an IGP (eg. RIP)

Dial related technologies
Dial-Related Technologies

  • COBRA (Central Office Based Remote Access) allow building of virtual POPs by backhauling PRIs

  • RADIUS (Remote Authentication Dial In User Service)

Integrated services digital network
Integrated Services Digital Network

  • ISDN customers authenticate by RADIUS similar to dial users

  • underlying architecture similar but dial equipment often administrated differently

  • ISDN maintained within same AS as backbone whereas dial often in its own AS

Ds 1 and high speed access
DS-1 and high-speed access

  • Customer connections usually multiplexed, come into DSU as a channelised DS-3

  • gateway routers on ISP side usually Cisco 7500 series, increasingly using Cisco 12000

  • customers connect using Cisco 1604, 2621, some 3600 series, very large customers use 7500 series routers

Gateway routers
Gateway Routers

  • obtain routes from customers usually statically, but sometimes by BGP

  • usually run link-state IGP within AS (eg. OSPF, IS-IS)

  • Cisco 7513 backplanes 1.8 Gbps while 12008 does 40 Gbps

Where does traffic go from here
Where does traffic go from here?

  • Most ISPs have two levels of networks above the access router

  • Metropolitan networks aggregate gateway traffic, generally city-wide (if multiple POPs in city)

  • transit networks aggregate metro network’s traffic, responsible for inter-city transport

Atm switches
ATM Switches

  • Terminate long-haul OC-12, OC-48 circuits and metro rings

  • Choice of vendor contingent on ISP, commonly Newbridge, Fore Systems (ASX-1000 and ASX-4000)

Example of an atm interface
Example of an ATM interface


interface ATM2/0

description To HA13.BLAH1 3C1

atm vc-per-vp 512

atm pvc 16 0 16 ilmi


interface ATM2/0.195 point-to-point

description To XR1.BLAH1 ATM6/0

ip address

ip router isis Net-Backbone

atm pvc 195 0 195 aal5snap

clns router isis Net-Backbone

Implementation of bgp
Implementation of BGP

  • BGP run between autonomous systems and peers, as well as multi-homed customers

  • monolithic AS broken up into BGP confederations for ease of work

  • routes controlled using access lists and route maps

Implementing and maintaining an isp backbone

  • Communities are destinations that share common attributes (eg. through access-list filters)

BGP table version is 23718690, local router ID is

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal

Origin codes: i - IGP, e - EGP, ? - incomplete

Network Next Hop Metric LocPrf Weight Path

*>i24.64.0.0/19 100 0 6327 6172 i

*>i24.64.0.0/14 100 0 6327 i

*>i24.64.32.0/19 100 0 6327 6172 i

*>i24.64.64.0/19 100 0 6327 6172 i

*>i24.64.96.0/19 100 0 6327 6172 i

*>i24.64.192.0/19 100 0 6327 6172 i

*>i24.64.224.0/19 100 0 6327 6172 i

*>i24.65.0.0/19 100 0 6327 6172 i

*>i24.65.96.0/19 100 0 6327 6172 i

*>i24.65.128.0/19 100 0 6327 6172 i

Advantages of bgp for user
Advantages of BGP for User

  • Allows for load-sharing and redundancy

  • routes can be biased through AS path prepending

  • requirement is high-quality router with close to 100% uptime to avoid connection flaps and subsequent route dampening

Common customer issues
Common Customer Issues

  • Static routes on backbone - often difficult to spot, can cause very strange routing results

  • pull-up routes for netblocks smaller than /24, required to avoid BGP dampening

  • BGP recalculations - if done on a transit router, entire backbone segments can experience outages

Customer requirements of the backbone
Customer Requirements of the Backbone

  • Redundancy - networks are redundant but card failures can take down whole routers

  • physical connection to POP from customer is SPF

  • low latency - massive increases in demand on backbone makes this difficult

  • over $2 million a day spent on global backbone upgrades

Dsl low cost high speed
DSL: low cost, high speed

  • DSL might phase out ISDN connections

  • difficult to troubleshoot from network standpoint

  • connections pass through telco’s frame or ATM cloud between DSLAM and VR

  • RedBack SMS (Subscriber Management System) 1000 commonly used as VR

Redback sms 1000
RedBack SMS 1000

  • Supports up to 4000 sessions

  • OC-3 out to metro network

  • traffic-shaping accomplished with profiles

atm profile samplecust


shaping vbr-nrt pcr 1000 cdvt 100 scr 100 bt 10

Increasing capacity
Increasing Capacity

  • Backbone capacity increasing at a huge rate

  • Traffic engineering combined with high backplane becoming increasingly important

  • many ISPs turning to Juniper routers

  • UUNET rolled out production OC-192c with Juniper M160 running MPLS

Juniper routers
Juniper Routers

  • JUNOS supports MPLS and RSVP

isis {

interface all;


ospf {

area {

interface so-0/0/0 {

metric 15;

retransmit-interval 10;

hello-interval 5;





Distributed dos attacks
Distributed DOS attacks

  • Can be very detrimental to backbone (even causing switch crashes)

  • Combated by rate-limiting ICMP on routers

  • Most effective defense is community-wide egress filtering; requires co-operation throughout the Internet

Canadian network challenges
Canadian Network Challenges

  • Geographically, population resides in virtually a straight line across the south

  • major focus is on southbound capacity to the US

  • CRTC regulations on telcos create different arrangements

  • heterogeneous network to the US, integration a big issue


  • Anything I can clarify or expand on...

  • Thank you!