Lecture 5 - Routing On the Flat Labels M.Sc Ilya Nikolaevskiy Helsinki Institute for Information Technology (HIIT) T – Special Course in Future Internet Technologies

2 Routing On the Flat Labels  Based on and pictures borrowed from:  Matthew Caesar, Tyson Condie, Jayanthkumar Kannan, Karthik Lakshminarayanan, and Ion Stoica. ROFL: routing on flat labels, SIGCOMM Comput. Commun. Rev. 36, 4 (August 2006)  I. Stoica, R. Morris, D. Lieben-Nowell, D. Karger, M. Kaashoek, F. Dabek, H. Balakrishnan. Chord: a scalable peer-to-peer lookup protocol for Internet applications, IEEE Transactions on Networks, 11(1) 17-32, 2003.

3 Flat Labels  Identification/location split:  Mobility, Multihoming  In this architecture – no location at all (routing on names)  No network semantics in the identities – any identities may be used => Flat Labels

4 Advantages  All advantages of location-identity split (multihoming, mobility, …)  No new infrastructure – no additional resolving  Fate-sharing: No need to contact resolution center  Simple allocation and management

5 Reason  Does the scalable routing require structured location information in the packet header?  Prior to ROFL all FIA rely on structural location information.

6 Chord  Scalable P2P lookup protocol  Given a key Chord maps it to the node.  Consistent hashing: when hashes space size changes only fraction of keys will have new hash  When node leaves or arrives only fraction of keys will be moved  Hashes space is a circle with 2 m points numbered in clockwise order

7 Chord: Consistent Hashing

8 Chord: Lookup

9 Chord: Lookup Optimization

10 Chord: Enhanced Lookup

11 Chord Conclusions  Each node stores small amount of information (O(log n))  Queries are fast (O(log n))  Easy to add/remove node from the system  Recovering techniques to heal from a node failure

12 ROFL Overview  Unique IDs for all nodes  3 types of nodes: routers, stable hosts, ephemeral hosts  Hosts are assigned to a gateway router  Same idea: all labels are organized in the circle. Routing is performed to the closest node not overrunning destination label.

13 Source Paths

14 Intra-domain Routing  In each AS there is a separate ROFL ring  Routing performed much like Chord lookup  Packets are forwarded in a greedy way: to the closest to the destination known node along the ring  Search similar to longest prefix match  Source paths to successors and predecessors are saved in all intermediate nodes in Pointer Cache to optimize packets paths

15 Host Join  Host registers in a gateway router  Router searches for predecessor of the host and update its’ successor  Router stores source path to the successor of host  Ephemeral hosts can not be successors

16 Inter-domain Routing  Hierarchical structure of ASes  Isolation property:  Failure isolation  Policies:  Provider-consumer  Peering  Multihoming

17 Hierarchical Ring Merging

18 Ring Merging Rules  Id b in Ring 2 is external successor of id a in Ring 1 iff:  Id b is a successor of id a in a joined ring  There are no nodes with identifiers in [id a, id b ] in either AS  Merges are performed at all levels of hierarchy  Each new host must be registered at all levels

19 Packet Forwarding  Essentially the same: forward packet towards Label closest to the destination and not overrunning it.

20 Handling Policies  Peering:  Virtual AS as a provider for peering ASes  Bloom filters to store all nodes in peering ASes  Multihoming:  Perform external join for each member of up-hierarchy  Bloom filters storing all hosts joined below AS are used before using pointer cache

21 Virtual AS

22 Evaluation  Intra-domain:  Trace based on “Rocketfuel” over 4 large ISPs with hundreds of routers and millions of hosts in each  Used 128-bit IDs  9 Mbits cache memory in routers  Inter-domain:  AS graph was derived from “Routeviews” traces  Simulation of 30,000 hosts extrapolated to 600 millions hosts

23 Evaluation: Intra-domain  Hosts typically complete join in less than 40ms with less than 45 control messages

24 Evaluation: Intra-domain (contd)  Average stretch depends on pointer cache memory: 1.2 to 2 for 9 Mbits of pointer cache

25 Evaluation: Inter-domain  Each AS is emulated by a single node  Only 30,000 hosts were emulated  Join across all provider requires ~445 messages  Average stretch is 2.5

26 ROFL Strengths  Redesign of internet architecture  location/identity split  Policy aware inter-domain routing  Cryptographic identities  Spoofing attacks are impossible (on cost of cryptographic signatures)  Implicit Certificates instead of DNS

27 ROFL Weaknesses  Not really scalable  Possible hash collision  Needs large pointer cache  Inter-domain routing requires large Bloom filters for all hosts in ASes below  How to recalculate them? Flooding?  Complicated failure recovery

28 Thank you for your attention! Questions? Comments?