Transcript DDOS - Distributed operating system

Bandwidth DoS Attacks and
Defenses
Robert Morris
Frans Kaashoek, Hari Balakrishnan, Students
MIT LCS
What is a Denial of Service Attack?
• Goal: make a service unusable.
• How: overload a server, router, network link.
• Focus: bandwidth attacks (“trinoo”, “tfn”).
Logical View of Attack Net
Attacker
Control Traffic
Master
Slave
Attack Traffic
Slave
Slave
Victim
Slave
Slave
Attack Targets
Router
ISP
Link
Customer’s
Router
Other
ISPs
Host
App
O/S
Other
Customers
Customer’s LAN
Attacks use IP Packets
IP Header:
Source Address
Destination Address
User Data
• Routers forward each packet independently.
• Routers don’t know about connections.
• Complexity is in end hosts; routers are simple.
Outline
• Case study: Yahoo.
– What happened.
– Analysis.
• Our framework for defense: RON.
Case Study: Yahoo Attack
• Early February 2000.
• Took Yahoo off the net for hours.
Yahoo’s Point of View
ISP
Router
Yahoo’s
Router
www.yahoo.com
1 Gbit/second
of Ping Response
packets.
Yahoo Attack Overview
Co-location
Centers
Other ISPs
Yahoo’s ISP
Yahoo
Attack Packet Generation
Leader
Slaves
Co-location
Center
M
S1
S2
Ping,
DST=bcast,
SRC=Yahoo
Ping Responses,
DST=Yahoo
Internet
…
Sn
What did the attack depend on?
•
•
•
•
•
Pervasive insecure hosts.
Fake IP source addresses.
Use of hosts as amplifiers.
Weak router software.
Difficulty of diagnosis.
Pervasive Insecure Hosts
• Required for disguise and to generate enough traffic.
• How do they break in?
– Buffer overruns.
– Typically Solaris and Linux.
– Highly automated.
• Defenses?
–
–
–
–
Better programming practices.
Disable services by default.
Firewalls, intrusion detection.
Motivation for deployment is not strong.
Fake IP Source Addresses
•
Two uses:
–
–
Hide the source of attack.
Part of weapon.
•
•
Example: SYN flooding.
Defense:
–
–
Ingress/egress filtering.
But motivation for deployment is not strong.
Attacker
SRC=Site2
Ingress Filtering
Site 1
Site 2
ISP 1
ISP 2
ISP 3
Victim
Use of Hosts as Amplifiers
• Attackers need this:
– To avoid using their own machines.
– To generate lots of traffic.
– To avoid detection via load monitoring.
• Two approaches:
– Break into 1000s of machines.
– Trick legitimate machines into generating
traffic.
Weak Router Software
• Routers themselves are often victims.
• Why?
– Forwarding and management compete for CPU.
– Control and data traffic compete for net b/w.
• Solutions?
– Simplify and partition.
Difficulty of Diagnosis
• Very little automatic support for traffic
analysis and correlation.
–
–
–
–
Is the high load legitimate?
What does the attack consist of?
Where does the attack come from?
How ask upstream routers to discard attack
packets?
• Defense: distributed analysis system.
Why are these attacks easy?
• Internet built around end-to-end principle:
– Most functions done by end hosts.
– Examples: reliable delivery.
• Advantages:
– Simplifies network core.
• Example: IP packet forwarding.
• Example: it’s easy to start an ISP.
– Anyone can introduce new services.
• Result: lots of innovation.
Why is defense hard?
• End-to-end principle conflicts with:
–
–
–
–
–
Centralized control.
Centralized monitoring.
Separation of data from control traffic.
Mandatory authentication.
Mandatory accounting.
RON Project
• End-to-end framework for:
– Cooperative statistics collection.
– Cooperative reaction to attacks.
– Fault-tolerant control and data routing.
• How: resilient overlay network (RON).
• Funded by DARPA/IA/FTN.
What is an Overlay Network?
N2
N3
N1
ISP1
ISP2
N5
N4
• Better routing functions built in end hosts.
• Can be used to build distributed defenses.
Why Distributed Defenses?
• Presence of attack obvious near victim.
– Not obvious near sources of attack.
– But control is easier near sources.
• Identifying attackers requires cooperation.
– Asymmetric routing.
– Fake source addresses.
Why Distribution is Hard
• RON itself is a target.
• Authorized communication between RON
nodes.
• Bandwidth attacks on RON nodes.
• Application-level DoS attacks.
• Political / deployment problems.
– Needs cooperation? Or single-organization?
Monitoring Scenario
1. Measure
N2
N3
Victim
N1
Backbone B1
2. Communicate
Backbone B2
3. Control
N5
N4
Attacker
Fault-Tolerant Routing
• Use Internet to connect multiple sites.
• Inter-ISP routing:
–
–
–
–
Ignores link quality.
Ignores many available paths due to policy.
Chooses only one path.
Reacts slowly.
• RON allows end-system control of routing.
Fault-tolerant Routing (2)
N2
N3
N1
Backbone B1
Peering
Point P
Peering
Point Q
Backbone B2
N5
Attacker
N4
Peer-to-Peer Networking
• Multi-organization overlays.
• Early work: Gnutella and FreeNet.
– Data replicated at many sites.
– Queries traverse reliable overlay.
– Explicit protection of virtual infrastructure.
Summary
• Raise the bar:
– Improve host security.
– Make it hard to fake IP addresses.
• Experiment with RON-like and peer-to-peer
architectures.