BGP Series Part 2: Monitoring Route Changes Young Xu, Product Marketing Analyst

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•  May 5th 2016 •  Intro to Autonomous Systems, the BGP protocol and

how routes are advertised and learned

BGP Webinar Series

•  June 16th 2016 •  How to visualize, diagnose and set alerts to detect

BGP hijacks and leaks

How BGP Works

Detecting Hijacks & Leaks

•  May 24th 2016 •  Explore data from routing change events and

learn how to detect BGP changes with alerts

Monitoring Route Changes

Optimizing AS Paths

•  July 26th 2016 •  Tips and tricks for using routing data to improve how

traffic flows into or out of your network

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About ThousandEyes ThousandEyes delivers visibility into every network your organization relies on.

Founded by network experts; strong

investor backing

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Recognized as "an innovative "

new approach

27 Fortune 500 5 top 5 SaaS Companies

4 top 6 US Banks

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45 monitors on 30+ networks

See inbound routing to your prefixes

Collecting BGP Data

Establish a BGP multi-hop session with ThousandEyes

See outbound routing

to key services and endpoints

Public Monitors Private Monitors

Your BGP speaker

ThousandEyes collector

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Visualizing BGP Routing

Origin AS (Comcast)

Public vantage points

Upstream ISP (Level3)

Upstream ISP (NTT)

Github prefix

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Visualizing Routing Changes

Withdrawn routes to Level3 New or updated

routes via Comcast

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Inside à Out Visibility: Private BGP Monitors

Amazon

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•  Routes change in two ways: 1.  AS Path vector changes

–  Doesn’t change the destination prefix –  Can change with new routes, withdrawn

routes or updated route preferences 2.  A more specific prefix appears or

disappears –  Changes the destination prefix –  Covered and covering prefixes can be

used to maintain multiple routing policies in the routing table

–  Routes can be quickly changed as needed

How Routes Change

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•  Policy and Peering Changes –  Commercial relationships –  DDoS mitigation –  Equipment failures – Maintenance

•  Routing misconfigurations –  Attribute confusion

–  Prepending errors –  Route flapping

•  Route hijacking and leaks – Others advertising your prefix – Or a more specific prefix

Types of BGP Changes

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•  Options to influence inbound routing to your network include: –  Introducing new routes

–  Advertising new routes –  Introducing a more specific prefix with a different route

–  Withdrawing routes –  Changing BGP attributes in route advertisements

–  AS path prepending –  Multi-exit discriminator (MED) –  Communities (e.g. NO-EXPORT); BGP conditional advertisements

•  Both the origin AS and upstream ISPs can make peering changes –  Monitor reachability and make sure that new routes are correct and propagated

•  Look for: One-time AS path change, new providers or prefixes –  Example: First Horizon changed ISPs by introducing a covered prefix.

lswfk.share.thousandeyes.com

Policy and Peering Changes

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•  Coordinated handover from upstream ISP TW Telecom to Level 3

Policy and Peering Changes: First Horizon

Time: 22:30 CDT Prefix: 198.72.78.0/23

Time: 22:45 CDT Prefix: 198.72.78.0/24

Changes in TW routes

Level 3 routes to new covered prefix

Severe packet loss issues, due to delay between withdrawn TW routes and new Level 3 routes

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•  BGP is commonly used to shift traffic to scrubbing centers of DDoS mitigation providers during an attack

•  Look for: Mitigation provider’s AS either appearing directly upstream from Origin AS or becoming Origin AS –  Example: Discover changed their upstream providers from AT&T

and Sprint to Prolexic. ugkspyenl.share.thousandeyes.com

DDoS Mitigation

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DDoS Mitigation: Discover

Sprint

AT&T

Withdrawn routes to

AT&T, Sprint

New routes through Prolexic

Prolexic

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•  Failures can occur on links or interfaces in upstream providers – May re-route on its own or may require intervention

•  Look for: Issues isolated within specific ISPs and subsequent routing changes –  Example: When upstream ISP Verizon experienced severe issues,

First Data made a BGP change and dropped Verizon. qoeaud.share.thousandeyes.com

Equipment Failures

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Equipment Failures: First Data New routes

through AT&T

Withdrawn routes to Verizon

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•  Common misconfigurations include: –  BGP attribute confusion

–  AS path prepending errors –  Route flapping –  Route leaks

•  Look for: Unexpected ASes, routes or route changes –  Example: Country Financial mistyped an AS when prepending the

AS path. tetuntn.share.thousandeyes.com

Routing Misconfigurations

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Routing Misconfigurations: Country Financial

Access2Go (correct ISP)

Mistyped AS (Jaguar Comms.) prepended to AS path

No routes to AS 15011 led to terminal paths and loops

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•  When routes alternate or are advertised and withdrawn in rapid sequence –  Usually from equipment or configuration errors – Often causes packet loss and performance degradation

•  Look for: Repeating spikes or elevated levels of route changes over time –  Example: Ancestry’s upstream ISP XO Communications

experienced a route flap. imjlgyfuk.share.thousandeyes.com

Route Flapping

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Route Flapping: Ancestry

All routes to XO withdrawn Routes to XO

re-advertised

Route flap led to convergence delay issues, where traffic had already

entered the network but no longer had the routes to leave

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Tuning Your BGP Alerts Scenario Threshold Peering Changes, Route Flaps

Path Changes > 1 Reachability < 100%

DDoS Mitigation Activation

Origin ASN in ___ Prefix not in ___ Next Hop ASN in ___

Prepending Errors Next Hop ASN not in ___

Prefix Hijacking, Leaks Origin ASN not in ___ Covered Prefix exists

Join us in Part 3 for a discussion on detecting BGP hijacks and leaks

See what you’re missing.

Watch the webinar:

www.thousandeyes.com/webinars/monitoring-route-changes