alternate path discovery in the internet
TRANSCRIPT
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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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IEEE-PNEC SPARKLE TALKS-DRSAMEER QAZI 2
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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IEEE-PNEC SPARKLE TALKS-DRSAMEER QAZI 3
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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IEEE-PNEC SPARKLE TALKS-DRSAMEER QAZI 4
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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IEEE-PNEC SPARKLE TALKS-DRSAMEER QAZI 5
BGP recovers lazily from faults!
BGP speakers
Destination
Source
On detectingfailure tryalternate paths
one by one
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IEEE-PNEC SPARKLE TALKS-DRSAMEER QAZI 6
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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IEEE-PNEC SPARKLE TALKS-DRSAMEER QAZI 7
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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IEEE-PNEC SPARKLE TALKS-DRSAMEER QAZI 8
Alternate Path discovery through
overlay/ p2p networksTriangle
Inequalityis violated!
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IEEE-PNEC SPARKLE TALKS-DRSAMEER QAZI 9
This Solution has its costs!
Packetlossra
te,Throu
ghput,Lat
ency
Dissem
inateallm
easureme
nts
Monitor Paths!
Share
Measurements!
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IEEE-PNEC SPARKLE TALKS-DRSAMEER QAZI 10
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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IEEE-PNEC SPARKLE TALKS-DRSAMEER QAZI 11
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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IEEE-PNEC SPARKLE TALKS-DRSAMEER QAZI 12
Overlay Network: Global Impact :~
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IEEE-PNEC SPARKLE TALKS-DRSAMEER QAZI 13
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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IEEE-PNEC SPARKLE TALKS-DRSAMEER QAZI 14
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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IEEE-PNEC SPARKLE TALKS-DRSAMEER QAZI 15
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