Alternate Path Discovery in the Internet

8/2/2019 Alternate Path Discovery in the Internet

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IEEE-PNEC SPARKLE TALKS-DRSAMEER QAZI 1

Alternate Path Discovery in

the Internet

Dr Sameer Qazi,

Asst Prof,

PNEC NUST


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Why Alternate Paths Help

Alternate path between two hostsoffering better QoS

Fetching content from anearby server

Reaching host B behind a firewallthat blocks incoming connectionsfrom host A but not host C

A B

A B

C

A B

Sending redundant packetsover multiple paths


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Border Gateway Protocol (BGP)

ASE

ASF

ASA

ASH

ASC

ASD

src dst

Destination prefix213.145.13.0/24

AS path/s: B C D (primary)E F DG H J D

213.145.13.12

ASG

ASB

ASJ


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BGP is QoS unaware

BGP definition: Path connects two points

Does not answer:

How much delay, latency,connectionthroughput, packet loss rates


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BGP recovers lazily from faults!

BGP speakers

Destination

Source

On detectingfailure tryalternate paths

one by one


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Modification to BGP to speed it up!

BGP speakers

Destination

Source

Routes invalidated by failure (dashed)

RouteWithdrawal

messages,

appendedwith cause-of-failuretags


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Multi-Homing

AS 20

AS 40AS 30

20.0.120.0/24

IP Prefix, {AS path}

40.0.0.0/8, {AS 40}

20.0.120.0/24, {AS 40 AS 20}

IP Prefix, {AS path}

30.0.0.0/8, {AS 30}

20.0.120.0/24, {AS 30 AS 20}

40.0.0.0/830.0.0.0/8

Inflates size of BGProuting tables

BGP accepts only largeblock, deletes smallblocks would prefer20.0.0.0/16 over20.0.120.0/24

Only offers last hopalternate pathsolution


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Alternate Path discovery through

overlay/ p2p networksTriangle

Inequalityis violated!


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This Solution has its costs!

Packetlossra

te,Throu

ghput,Lat

ency

Dissem

inateallm

easureme

nts

Monitor Paths!

Share

Measurements!


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Drafting Approaches

Direct Internet Path suffers from outage/service degradation

One-hop Indirection using an overlaynode near a server preferred byAkamai,- to serve content

Servers preferred by Akamai

Servers NOT preferred by Akamai

Overlay nodes

Select overlay node near a serverpreferred by Akamai-to servecontent


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Time Based Vs Space Based?

AS A AS B AS C AS D AS E

AS P AS QAS R

Default Internet Path

Alternate Path diverges earliest fromdirect path

Source Destination

AS S


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Overlay Network: Global Impact :~


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Multi-Domain Path Negotiation

W. Xu and J. Rexford, "MIRO:multi-path

interdomain routing," inSIGCOMM '06: Proceedings ofthe 2006 conference onApplications, technologies,architectures, and protocols forcomputer communications,2006, pp. 171-182.


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Multi-Domain Path Set up

W. Xu and J. Rexford, "MIRO:multi-path

interdomain routing," inSIGCOMM '06: Proceedings ofthe 2006 conference onApplications, technologies,architectures, and protocols forcomputer communications,2006, pp. 171-182.


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MPLS path construction

PCE PCE PCE

Head

endnodes

TED TEDTED

src

dst

PCCPCC PCC

LSRs

PCC=path computation client TED=Traffic Engineering Databse

PCE=path computation element LSR=Label Switching Router

Alternate Path Discovery in the Internet

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