Pathlet routing CS513

1. PATHLET ROUTING
Amit Srivastava
Gauri Pulekar

2. Introducing, ‘Pathlet Routing’
 ACM SIGCOMM Computer Communication Review 2009
 Proposed by research team from UC Berkeley and UI Urbana Champaign
 Addresses two main problems with BGP
 Scalability
 Multipath Routing
 Allows protocol emulation, it can mimic BGP

3. BGP : It runs the internet!
 Current de-facto inter AS routing protocol
 BGP uses destination based forwarding i.e. IP address in the header
 Uses TCP connection to peers for sending information
 Only shares a portion of the routing table
 No periodic update to routing information
 Routers in the same AS are internal peers, others are external peers

4. BGP : Messages
 KEEPALIVE message sent for checking connectivity
 NOTIFICATION are for failure or before closing connections
 UPDATE messages carry routing information
 Routes are stored in Routing Information Bases (RIB):
 Adj-RIB-In contains information from inbound UPDATE messages, mostly
unprocessed information
 Loc-RIB contains local routing formation by applying local policies on the data in
Adj-RIB-In
 Adj-RIB-Out contains the routing info the router has selected to share with its
peers via UPDATE

5. Building Blocks
 Vnodes:
 Virtual node
 For a given router, it can have n vnodes for n interfaces
 This allows traffic shaping for traffic coming from an interface
 Routers learn about vnodes in the AS by exchanging information with peers
 Pathlets:
 A sequence of vnodes leading to a destination identified by a IP prefix
 Forwarding Identifier – FID (f)
 Vnode + Pathlet = Virtual topology

6. Let’s understand..
 Constructing pathlets between peer routers
A B
C
2

7. Let’s understand..
 Two pathlets used to send data from A to C
3
A B C
2
2, 3 3

8. Let’s understand..
 Three autonomous systems
3
A B C
2
4
4 3

9. Let’s understand..
 Three autonomous systems
A
B
C
y v
qr
s

10. Let’s understand..
 Ingress and egress points can be chosen from many available options
A
B
C
x v
qr
s

11. Let’s understand..
 Multiple pathlets to suit local transit policies
A
B
C
x v
qr
s

12. Pathlet Routing - Working
 Pathlet originates at a router R1 (with vnode v1)
 The sending vnode refers to its table for possible pathlets to reach
destination
 Creates a list of vnodes and calls it a pathlet ( and can advertise it) puts
the pathlet in the header and send the packet out to a peer
 Peer removes its own vnode in the packet header and sends along to the
next vnode
 This path selection is dependent on local policies of the AS

13. Route Selection
 Using shortest path algorithm
Path for packet forwarding based on result of shortest path algorithm run on a
graph created by using routing information at vnodes

14. Pathlet Dissemination
 Path vector algorithm (just like BGP)
 Announces pathlet’s FID and sequence of vnodes
 Scalability: Propagate arbitrary subset of known pathlets
 Path vector used for sending routing info not routing data

15. Components Of Pathlet Routing

16. Components Of Pathlet Routing
 Controller: Processes the routing information
 Vnode Manager: Manages all vnodes(tables) on a single device
 Disseminator: Sends out routing information to peers
 Router : Router running at least 1 pathlet routing instance
 Vnode: A small routing table
 Pathlet: A sequence of vnodes

17. Implementation: Router
 The router can have max 5 interfaces
 It can connect to other routers using TCP
 The topology is created using a config file
 There are 2 kinds of messages
 Data messages with dummy data
 Routing messages contain routing information in the following format
{AS-id, RouterId, VnodeId} and {PathletId (FID), IP Prefix}
 Routers collect stats like size of table in Vnodes and total control
messages sent and received
 Allow commands on each router

18. Implementation: Vnode & Vnode
Manager
 Vnode Manager is a container for Vnodes
 All VNodes have vnode-id, router-id, AS-id to uniquely identify it
 Controller logic is still being decided but it only decides on installing paths
from peers on Vnodes
 The shortest path algorithm is implemented on the Vnode
 The shortest path algorithm implemented separately but buggy

19. Implementation: Deciding Topology
 Using BGP RIB and Update messages to create update messages
 A simple 3 and 6 node topology being used to achieve basic goal of
routers exchanging data
 Currently tables are static

20. Scope
 Implement the software router in Python using Twisted and NetworkX.
 Allow exchange of messages on routers arranged in real-world like
scenario
 Save the logs for comparison with data from RouteViews
 Simulate loss of links

21. Timeline
Activity Completed Time
Find internet-based topology data or a
random graph which can be scaled from 10
to 300 nodes
20 October
Learn and implement the shortest path and
Path Vector algorithms
20 October
Learn basic Erlang. We are using Python
with NetworkX and Twisted
27 October
Explore possible packet structure for Pathlet
routing
27 October
Finalize the details to be implemented or
BGP and Pathlet routing
3 November
 Activities completed so far

22. Timeline
Ongoing Activities Time
Run the algorithms for Pathlet and BGP on a
large 100+ node graph. And verify the result
10 November
Simulate of a 3 node graph running BGP and
Pathlets capable of exchanging information.
Created a graph of 6 nodes to implement
Pathlet only not BGP
17 November
Verify the above system for discrepancies 24 November
Add provision for emulating Local policies for
implementing Local Transit policies
1 December
Run comparison studies on the system 8 December
 Ongoing activities and future plan

23. References
 http://dl.acm.org/citation.cfm?id=1592583
 https://www.ietf.org/rfc/rfc1771.txt
 http://jad-reads.blogspot.com/2009/04/thoughts-on-pathlet-
routing.html
 ftp://espectrocrom.com/pub/manuales/bgp/cisco%20-%20bgp%20-
%20internet%20routing%20architectures%202ed%20(press%201-
57870-233-x).pdf
 http://web.engr.illinois.edu/~pbg/pathlets/

24. Questions

25. Thank You