Gnutella2: A Better Gnutella?

1
Gnutella2 A Better Gnutella?

• COMP 5204 Data Networks
• Julie Thorpe
• School of Computer Science
• Carleton University

2
Introduction

• Gnutella and Gnutella2 are P2P application
  protocols.
• Gnutella has an interesting history essentially
  a reverse engineered Beta version.
• Changes governed by Gnutella Developers Forum
  (GDF).
• Gnutella2 is a completely different protocol than
  Gnutella, claiming it's what Gnutella should have
  been.
• The GDF reject this claim, and refuse to call
  Gnutella2 by its name they instead call it
  Mike's Protocol.
• Unclear whether Gnutella2 better than Gnutella.
• My project goal is to compare these protocols to
  determine which is theoretically better.

3
Presentation Outline

• Gnutella review
• Gnutella's problems
• Gnutella2 review
• Comparison
• Network architecture
• Searching algorithms
• Cooperation incentives
• Security
• Concluding remarks

4
Gnutella Review (1)

• Purely decentralized, simple protocol for file
  sharing.
• Runs over TCP/IP connections.
• New node enters Gnutella network by connecting to
  a known server (sends Ping), and when server
  responds (sends Pong) they are now connected
  peers.
• Learns of other nodes if server forwards Ping to
  its peers (and gets a Pong back in response).

5
Gnutella Review (2)

• Has no way to advertise files.
• Peers find files by flooding with query
  requests (stop after TTL hops).
• Query responses are routed back along the same
  path as the request arrived upon.
• Addressed by GUIDs.

6
Gnutella's Problems

• Scalability.
• Performance.
• Lack of cooperation incentives.
• Abuse by servents (Gnutella client/server
  program).

7
Gnutella's Problems - Scalability

• For a node to be reached by a query, it (and all
  other nodes on the path to it) must be forwarded
  the request!
• The reach is determined by n ( connections to
  other hosts) and TTL ( hops each request is
  permitted to take)
• Assumption nodes all have the same n and TTL.
• Ritter 1 estimated that for reasonable
  parameters, to achieve a reach of 106 nodes,
  Gnutella nodes must have a bandwidth between 19.2
  and 64 Gbps!

8
Gnutella's Problems - Performance

• Messages are forwarded through many other peers
  on the network.
• Connection speeds are effectively restricted to
  the bandwidth of the slowest peer along the
  route.
• If A and B have high-speed connections, and C has
  a modem connection, the download rate between A
  and B is limited to C's speed.

9
Gnutella's Problems Lack of Cooperation
Incentives

• One study found that over 70 of users shared no
  files, and 50 of all responses are returned by
  the top 1 2 .
• Implications of free-riders on Gnutella
• Increased search horizon (farthest set of hosts
  reachable by a search request, directly related
  to its TTL).
• The top 1 that is providing most files reaches
  connection saturation.
• This generally a difficult problem to solve for
  purely decentralized systems.

10
Gnutella's Problems Abuse by Servents

• Since it's a protocol, implementations can
  implement the Gnutella protocol as they please
  (in theory).
• Servents can act selfishly to improve their
  performance
• Increasing TTL to increase search horizon
  (generating geometrically higher messages).
• Frequent re-querying (generating more messages,
  degrading network).

11
Gnutella2

• GDF recommended (in version 0.6) ultrapeers to
  improve Gnutella's performance and scalability.
• Gnutella2 enforces a variation of this to improve
  performance and scalability.
• Decentralized, 2-tier hierarchy of peers (leaf
  nodes and hubs).
• Other important differences will come out in
  comparison.

12
Comparison Gnutella vs. Gnutella2

• Network architecture
• Searching algorithms
• Cooperation incentives
• Security

13
Gnutella's Network Architecture

• Recall it is completely decentralized.

14
Gnutella2's Network Architecture

• Decentralized, 2-tier.
• This architecture is recommended for Gnutella in
  v0.6.
• New node enters by connecting to a known hub
  (almost identical to Gnutella's handshake).
• Hubs typically accept 300-500 leaves, and connect
  to 5-30 other hubs.
• Leaves typically connect to 3 hubs.

15
Comparison Network Architecture

• Gnutella's purely decentralized is much simpler,
  but not as scalable.
• No real difference between Gnutella's v0.6
  ultrapeer structure and Gnutella2's hub
  structure.
• Either of these strategies should reduce
  searching traffic as explained in searching
  algorithms.

16
Gnutella's Searching Algorithm

• Recall that using the purely decentralized
  version, packets are flooded throughout the
  network.
• If the v0.6 ultrapeer recommendation is
  implemented, searching is optimized using Query
  hash tables(QHTs).
• A QHT is maintained by each node, and describes
  the content it is sharing.
• An ultrapeer maintains an aggregate of its leaf's
  QHTs and its own QHT.
• Searches are performed by forwarding a query to
  an ultrapeer, who checks its aggregate QHT for a
  match.
• If there is a match, the query is forwarded to
  the appropriate leaf, otherwise the query is
  forwarded to neighbouring ultrapeers by
  flooding.

17
Gnutella2's Searching Algorithm

• Ultrapeers are called hubs.
• Uses a QHT like Gnutella, but if a hub cannot
  match a query to its aggregate QHT, it checks a
  set of caches
• Each hub maintains a cached copy of each
  neighbouring hub's aggregate QHT.
• Upon a search miss, a hub will try to match the
  query against its cached copies of its neighbours
  QHTs.
• If the query matches, it will forward the query
  once, and the node that receives the query
  processes it and directly sends the result back
  to the client.
• If no match is made, the searching client will
  continue at another untried hub.

18
Comparison Searching Algorithms

• Both Gnutella with Ultrapeers and Gnutella2
  significantly reduce the number of messages.
• Should increase performance and scalability.
• Gnutella2's method further reduces the number of
  messages sent for a query
• Less query request messages due to caching
  neighbour's QHTs.
• Less response messages since Gnutella2's method
  allows the responding node to directly contact
  the requesting node, rather than sending the
  message back through the path to get there.

19
Comparison Cooperation Incentives

• Neither Gnutella nor Gnutella2 specify
  cooperation incentives.
• Implementations often will not allow connections
  to network unless you share something, and by
  default make downloads shared.
• The problem of cooperation incentives in a
  decentralized environment is interesting, since
  nodes can avoid connecting to those that have a
  profile of their behaviour.

20
Gnutella's Security

• Gnutella's query messages are routed through
  peers, and the query does not contain the
  querying node's IP address, but a Globally Unique
  Identifier (GUID).
• Provides anonymity by masking requester's
  identity.
• Denial-of-service (DOS) attacks are possible by
  flooding the network with many requests with a
  fake GUID.
• Another node could be similarly DOS'ed if a GUID
  for one of their request GUIDs is known.
• Response IP addresses could be spoofed and
  malicious content provided.

21
Gnutella2's Security

• Gnutella2 does not use GUIDs for queries
• Sends the response directly back to the
  requesting node.
• The QHTs do not contain information about the
  content stored on a neighbouring node, providing
  privacy.
• Queries make use of query keys (to verify the
  query return address is that of the original
  sender).
• Prevents malicious users from sending out queries
  for the purpose of flooding the network with
  spoofed requests.
• Search clients only permitted to query a hub
  after obtaining a query key, which are unique
  to each (hub, search client return address) from
  it to include in the transmission.

22
Comparison - Security

• Both Gnutella with ultrapeers and Gnutella2
  provide privacy through their caching.
• Both Gnutella and Gnutella2 are suceptible to
  spoofed response IP addresses.
• For Gnutella2
• Gnutella does not provide authentication of nodes
  for querying, thus it is susceptible to request
  flooding attacks.
• Gnutella ultrapeers cannot block certain hosts
  (do not have query keys or unique request
  addresses).
• For Gnutella
• Gnutella2 does not provide anonymous queries.

23
Concluding Remarks

• Gnutella has some serious flaws (scalability,
  performance, lack of cooperation incentives and
  servent abuse).
• Gnutella2 solves all but cooperation incentives.
• Gnutella with ultrapeers solves scalability and
  performance, but the searching algorithm and
  caching is less sophisticated.
• Gnutella2 has many more features outside of this
  comparison, primarily being more extensible (yet
  specific) to support applications other than file
  sharing.
• Although they are different protocols, Gnutella2
  is in essence, an improved version of Gnutella
  with ultrapeers.

24
Open Problems

• Is it possible to create useful cooperation
  incentives in a large, truly distributed
  environment like Gnutella where peers may
  reconnect to different hubs upon connection?

25
References

• Jordan Ritter, Why Gnutella Can't Scale. No,
  Really., http//www.tch.org/gnutella.htm.
• Eytan Adar and Bernardo A. Huberman,
  Free-Riding on Gnutella, http//www.firstmond
  ay.org/issues/issue5_10/adar/index.html.
• Farhad Manjoo, Gnutella Bandwidth Bandits,
  Aug. 8, 2002.
• RFC-Gnutella 0.6, http//rfc-gnutella.sourceforg
  e.net/developer/testing/index.html.
• Anurag Singla and Christopher Rohrs,
  Ultrapeers Another Step Towards Gnutella
  Scalability, Version 1.0, http//rfc-gnutella.so
  urceforge.net/src/Ultrapeers_1.0.html
• Gnutella vs. Gnutella2, Part 1,
  http//www.mp3newswire.net/stories/2003/gnutella.h
  tml.
• The Gnutella2 Developers Network.
  http//www.gnutella2.com.
• LimeWire Network Improvements,
  http//www.limewire.com/developer/net_improvements
  .html
• P2P Networking Technologies. URL
  http//ntrg.cs.tcd.ie/undergrad/4ba2.02-03/Intro.h
  tml.