A Suite of Schemes for User-level Network Diagnosis without Infrastructure
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A Suite of Schemes for User-level Network Diagnosis without Infrastructure
Yao Zhao, Yan ChenLab for Internet and Security Technology, Northwestern University
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Motivation
• How do end users, with no special privileges, identify packet loss inside the network with one or two computers?
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Motivation
• How do end users, with no special privileges, identify packet loss inside the network with one or two computers?
• Take-home– We propose three user-level loss rate
diagnosis approaches– The combo of our approaches and
Tulip [SOSP03] is much better than any single approach
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Outline
• Motivation• Related Works• Lossy Link Diagnosis
– Fragmentation Aided Diagnosis (FAD)• Algebraic FAD• Opportunistic FAD
– Striped Probe Analysis (SPA)• Evaluations• Conclusions
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Related Work I
• Internet Tomography– Multicast based (not practical)– Unicast based
• Mimic multicast
L1 L2 L3 L4
S
Virtual
link
The more cooperating end
hosts, the shorter the virtual links
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Related Work II
• Tulip [SOSP03]– Leverage on consecutive IPID– Tend to underestimate forward loss
rates• Suffer from the packet loss correlation
x
id
id+1
Forward Loss
S D
xid
id+2
Reverse Loss
S D
xid
S D
x
?
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Outline
• Motivation• Related Works• Lossy Link Diagnosis
– Fragmentation Aided Diagnosis (FAD)• Algebraic FAD• Opportunistic FAD
– Striped Probe Analysis (SPA)• Evaluations• Conclusions
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Link Diagnosis=> Forward Path Diagnosis
• If we can infer the loss rates of forward path F1 and F2, we can infer the link loss rate of l3
F1
DS R1 R2
F2
l3l2l1
• The more diagnosable forward path segments, the better the diagnosis granularity
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Basic Idea of FAD
S NP R
P
R
S NP1 RP2R
P1
P2
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Algebraic FAD
• Let pf and pr be the loss rate of the forward and reverse path respectively
P
R
R
P1
P2
(1 - pf)×(1 - pr)=1 – p (1)
(1 - pf)2×(1 - pr)=1 – p’ (2)
p and p’ are measurable. Solve pf and pr using (1) and (2)
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How to Achieve FAD
IP Fragmentation– Fragment a packet longer than MTU– Required to be supported in IPv4– Some routers disable it for security reason
• Support of IP Fragmentation– 64,320 router IP addresses probed by using Tr
aceroute– About 80% of routers support IP fragmentation
• Degree of Rate Limiting on Responses– 99% of routers allow a rate of 100 probes/s for
ICMP Echo, ICMP Timestamp and TCP probes– Response to UDP probe is severely rate-limited
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Opportunistic FAD
F1 F2+ P
F’2F1 + P’
aaaaaaaa bbbbbbbb aaaaaaaabbbbbb
aaaaaaaa ccccccccc aaaaaaaacccccccc
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Opportunistic FAD
R’
Forward Loss
F1
xF
2
F’2R
No Loss
S NF
1
F2
F’2 F1+F2
F1+F’2
S N
Similar to Tulip, but OFAD allows large gap between fragments
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Striped Probe Analysis (SPA)
• S sends a probe to D and we get the path p1->p2
• S sends UDP packet with a certain TTL so that R returns an ICMP TTL-Exceeded response. Hence we get path p1->p3
S
p1
p3
p2 DR
S
R
D S
p1
p2 p3
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Striped Probe Analysis (SPA)S
R
S
p1
p2 p3
P1 P2
(1) Loss on shared link
D
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Striped Probe Analysis (SPA)
• Success rate of p1≈n1×n2 / (n×n12) – n: number of striped probes sent, – n1: number of P1 received by D, – n2: number of P2 received by S, – n12: number of cases that both P1 and P2 are received
• Unbiased if packet loss has perfect correlation and loss rates of different links are independent
S
R
S
p1
p2 p3
P1 P2
(2) Loss on non-shared link
D
S
R
S
p1
p2 p3
(1) Loss on shared link
D
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Summary
Requirement Accuracy
Tulip [SOSP03] Consecutive IPID (70%) Inaccurate w/ strong loss
correlation
FAD (AFAD & OFAD) IP fragmentation (80%) Accurate w/ weak or short loss
correlation
SPAICMP TTL-Exceeded. Access from both end hosts
Accurate w/ strong loss correlation
The current Internet usually has strong but short loss correlation.
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Outline
• Motivation• Related Works• Lossy Link Diagnosis
– FAD– SPA
• Evaluations• Conclusions
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Evaluation Metrics
• Diagnosis Granularity– Weighted average of the lengths of the
path’s diagnosable segments– For example, an 8-hop path has two
diagnosable segments of length 3 and 5, and then the granularity of the path is (32 + 52)/8 = 4.25
• Accuracy– Estimation error: – Relative error:
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Diagnosis GranularitySPA
is best
FAD ≈Tulip
Combo of FAD and
Tulip is better
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Path-Level Accuracy Evaluation
FAD > Tulip > SPA
OFAD, Tulip and SPA tends to underestimate
loss rates
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More Evaluations
• Consistency Check• Packet Probe Size Selection• Lossy Link Distribution• More in the technical report
http://www.cs.northwestern.edu/~yzh734/
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Conclusions and Recommendations
• We propose AFAD, OFAD and SPA which can conduct loss rate diagnosis without infrastructure
• Tulip, FAD and SPA have different working scenarios– The combination of them can achieve low diagn
osis granularity and high accuracy• Recommendations
– OFAD+SPA, if we can control the two ends of an end-to-end path
– OFAD+Tulip, if we can only control the source
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Thanks!
Questions?
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Path-Level Accuracy of Combined Schemes
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Path-Level Accuracy Evaluation
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Path-Level Accuracy of Combined Schemes
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IP Fragmentation Is Widely Supported• Router Collection
– 64,320 router IP addresses probed by using traceroute from a machine
• Support of Different Probes
• Support of IP Fragmentation– 90.3% of responsive routers support IP fragmentation– Altogether about 80% of routers support FAD.
• Degree of Rate Limiting on Responses– 99% of routers allow a rate of 100 probes/s for ICMP Echo,
ICMP Timestamp and TCP probes– UDP probe is severely rate-limited
Echo Timestamp UDP TCP Any
1 source 85.3% 69.2% 64.5% 71.7% 88.2%
10 sources 87.3% 72.3% 70.7% 73.3% 90.1%
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Packet Transmission Correlation• Choose 100 PlanetLab hosts and
randomly measure 5000 paths• Little loss correlation with enough gap
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Forward Path Diagnosis => Link Diagnosis
• If we can infer the loss rates of forwarding path l1 and P1, we can infer the link loss rate of l2 too.
D
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Opportunistic FAD
• n: number of R12 received, n’: number of R’12 received
• Xi = 0 when forward packet i is lost and Xi =1 otherwise
• P(X2=1)≈P(X2=1|X1=1)≈n/(n+n’)
R12
P1
P2
P’2R’12
P1
P2
P’2
x
(1) (2)
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Striped Probe Analysis (SPA)
• No fragmented packets needed !• S sends a probe to D and we get the path l1->l2
• S sends UDP packet with a certain TTL so that R returns an ICMP TTL-Exceeded response. Hence we get path l1->l3
S R
l1
l3
l2
S
R
D S
l1
l2 l3
D
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Striped Probe Analysis (SPA)
S
R
S
l1
l2 l3
P1 P2
D
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Striped Probe Analysis (SPA)
S
R
S
l1
l2 l3
P1 P2
(1) No loss (2) Loss on shared link
S
R
S
l1
l2 l3
P1 P2
D D
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Striped Probe Analysis (SPA)
• Success rate of l1≈n1×n2 / (n×n12) – n: number of striped probes sent, – n1: number of P1 received by D, – n2: number of P2 received by S, – n12: number of cases that both P1 and P2 are received
• Unbiased if packet loss has perfect correlation and loss rates of different links are independent
S
R
S
l1
l2 l3
S
R
S
l1
l2 l3
P1 P2
(1) No loss (2) Loss on shared link (3) Loss on non-shared link
S
R
D S
l1
l2 l3
P1 P2
D D