1. Automated Network Repair with Meta Provenance
Fix it!
Yang Wu* Ang Chen*
Andreas Haeberlen* Wenchao Zhou Boon Thau Loo* * University of Pennsylvania Georgetown University
Y. Wu
HotNets-2015 (Nov 17, 2015)

2. server not getting requests?
Motivation: Automated repair
Networks can have bugs
How can we find and fix bugs quickly?
else if (switch == S1 && protocol == HTTP) then action = output:3.
Copy-and-paste bug!!!
else if (switch == S1 && protocol == HTTP) then action = output:5.
SDN
Controller
Why is the backup web
server not getting requests? S0 5 S2 3 4 S1
Backup
Web Server
Main
DNS
Server
Off-loading
HTTP
HTTP traffic
Y. Wu
HotNets-2015 (Nov 17, 2015)

3. Goal: Automated repair
Existing debuggers can identify problems
But finding effective fixes is still hard
Can we automate this?
Goal: “Fix it!” button for networks
NetSight (NSDI 2014):
requests dropped at S2
Treated as given! S0
SDN
Controller 5 S2 3 4 S1
Backup
Web Server
Main
DNS
Server
Why is the backup web
server not getting requests?
How to make the backup web server get requests?
Off-loading
HTTP
Y. Wu
HotNets-2015 (Nov 17, 2015)

4. HTTP Packet received at Main Web Server
Approach: Meta provenance
Problem: Finding fixes is hard
Idea: Provenance can pinpoint the root cause
But previous provenance focus exclusively on data
Key idea: Treating program as data
meta
provenance
HTTP Packet received at Main Web Server
Matching Flow Entry
installed at S1
PacketIn
received at Controller
Executed If Clause
in Controller Program
Y. Wu
HotNets-2015 (Nov 17, 2015)

5. Output: Possible repairs
How could meta provenance be used?
Press
“Fix it!”
No HTTP Packet
received at H2
No Matching Flow Entry
installed at S2
No Executed If Clause
in Controller Program
No Specific Constant
Meta provenance
is generated
Output: Possible repairs
How to make the backup web server get requests?
Fixed!
Fix it!
Change “switch == S1”
to “switch == S2” …
Y. Wu
HotNets-2015 (Nov 17, 2015)

6. Overview Solution Goal: “Fix-it!” button for SDNs
Challenge: Cannot reason about program changes
Goal: “Fix-it!” button for SDNs
Approach: Meta provenance
Overview
Mete provenance model
Generating repairs
Solution
Practical challenges
Case study

7. Meta provenance model Constant(“S1”) Provenance Meta Provenance
Explains which inputs contribute to the outputs
Explains which parts of the program contribute to the outputs
Tuples: inputs, outputs
Meta tuples: inputs, outputs, syntactic elements of the program
Program: how input derives output
Meta program: how the programming language operates
Matching Flow Entry
installed at S1
PacketIn
received at Controller
Matching Flow Entry
installed at S1
Executed If Clause
in Controller Program
PacketIn
received at Controller
Constant …
Constant(“S1”)
FlowEntry(“S2”, “HTTP”, “Output-1”)
if (switch == S1 && protocol == HTTP) then action = output:5
if (operator == “==” && variable == constant)
then expression = true

8. HTTP Packet received at Main Web Server
Meta provenance: Example
Finds relevant syntactic elements
else if (switch == S1 && protocol == HTTP) then action = output:3.
else if (switch == S1 && protocol == HTTP) then action = output:5.
HTTP Packet received at Main Web Server S0 1
SDN
Controller 5 S2 3 4 S1
Backup
Web Server
Main
DNS
Server
Matching Flow Entry
installed at S1
Executed If Clause
in Program …
HTTP traffic
Satisfied Condition
in Program …
Operator ==
in Program
Variable
in Program
Constant
in Program
Y. Wu

9. Overview Solution Goal: “Fix-it!” button for SDNs
Challenge: Cannot reason about program changes
Goal: “Fix-it!” button for SDNs
Approach: Meta provenance
Overview
Mete provenance model
Generating repairs
Solution
Practical challenges
Case study

10. received at Controller No Satisfied Condition
Generating repairs
counter-factual reasoning generates targeted repairs
else if (switch == S1 && protocol == HTTP) then action = output:5.
else if (switch == S1 && protocol == HTTP) then action = output:3.
No HTTP Packet
received at H2
Negative provenance
(SIGCOMM 2014) S0
SDN
Controller 5 S2 3 4 S1
Backup
Web Server
Main
DNS
Server
No Matching Flow Entry
installed at S2
Off-loading
HTTP
No Executed If Clause
in Controller Program
PacketIn
received at Controller
No Satisfied Condition
in Controller Program
Change “switch == S1”
to “switch == S2”
Operator ==
in Program
Variable
in Program
Wrong Constant
in Program
Y. Wu

11. Practical challenges: Infinite repairs
Problem: Meta-provenance tree is infinite
Idea: Programmers make certain errors more often
We can explore repairs in cost order, up to some cut-off
Other challenges are discussed in the paper
Y. Wu
HotNets-2015 (Nov 17, 2015)

12. How to make the backup web server get requests?
Case study
We built an initial prototype of a debugger
We defined a meta provenance model for NDLOG
Our prototype fixed the copy-and-paste bug automatically
else if (switch == S1 && protocol == HTTP) then action = output:5. S2
else if (switch == S1 && protocol == HTTP) then action = output:3. S0
SDN
Controller 5 S2 3 4 S1
Backup
Web Server
Main
DNS
Server
How to make the backup web server get requests?
Off-loading
HTTP
Fix it!
Y. Wu

13. Summary Goal: Automated repairs for networks Approach: Meta Provenance
Ideally, can we have an automatic “Fix it!” button?
Approach: Meta Provenance
An extension of network provenance that treats program as data. Uses counterfactual reasoning to generate targeted repairs.
Several interesting challenges
Example: Provenance trees are infinite.
We are currently building a complete debugger based on meta provenance
Questions?
Y. Wu
HotNets-2015 (Nov 17, 2015)