INTERNET TOPOLOGY MAPPING INTERNET MAPPING PROBING OVERHEAD MINIMIZATION  Intra- and inter-monitor redundancy reduction IBRAHIM ETHEM COSKUN University of Nevada, Reno M.Sc.

TOPOLOGY OF THE INTERNET Network of networks linked together world wide WHY IMPORTANT?  Identify vulnerabilities  Identify threats  Create new protocols  Examine internet evolution  Economics (Internet based services)

An autonomous system (AS) is a network or a collection of networks that are all managed and supervised by a single entity or organization. TOPOLOGY OF THE INTERNET AS 1 AS 2 AS 4 AS 3 Interconnection of Autonomous Systems (Internet Service Providers, Universities, Companies) Distinct regions of administrative control

Connection between ASes  AS needs to know how to reach the rest of the Internet BGP (Border Gateway Protocol)  provides reachability across the whole Internet  exchange routing information between ASes  iBGP, eBGP  eBGP: Border router  a direct link to another border router in another AS TOPOLOGY OF THE INTERNET AS 1 AS 2

 Traceroute  Sends a series of probes to successive nodes along a route to a destination  Records source address and time delay of the message returned by each hop. Tools for Topology Mapping

Figure: Tony McGregor RIPE NCC Visiting Researcher The reason of sending 3 packets is to calculate the average RTT. Traceroute RTT: the delay between sending the packet and getting the response

 Probing Overhead  Causes DoS attacks  Reduces efficiency THE PROBLEM

 Intra –monitor redundancy  Occurs when all traceroutes start from a single point  Inter –monitor redundancy  Occurs when multiple monitors visit the same point INTRA AND INTER –MONITOR REDUNDANCY

INTRA –MONITOR REDUNDANCY Monitor 1 Destination 1 Destination 2 Destination 3

INTER –MONITOR REDUNDANCY Monitor 1 Monitor 2 Monitor 3 Destination 1

 Introduced by Benoit Donnet, Philippe Raoult, Timur Friedman, Mark Crovella  Significantly reduces both kinds of redundancy: inter- and intra- monitor  Key ideas:  utilize tree-like structure of routes  probe each target by starting midpoint of the path DOUBLETREE

 Intra-monitor: Monitor-Rooted tree  Start probing far from the monitor (vantage point)  Probe forwards and backwards  If an interface is encountered that has already been discovered by the vantage point:  stop probing  add the discovered interface to the “local stop set” DOUBLETREE

Doubletree: Monitor-Rooted Tree Intra-Monitor

 Inter-monitor: Destination-Rooted tree  Probe forwards and backwards  If facing an interface that has already been discovered  stop probing  add the discovered interface to the “global stop set”  Monitors (vantage points) need to share information of discovered interfaces  VPs have to work in coordination DOUBLETREE

Doubletree: Destination-Rooted Tree Inter-Monitor

 Must determine a paths mid point  Information sharing between nodes causes another traffic  Doesn’t deal well with load balancing DOUBLETREE

 Reduce intra-monitor redundancy by performing partial traces to some destination IP addresses.  Once having a full trace to an IP address in an AS,  start traceroute queries from the hop distance h i of the ingress router  If the first IP of the new trace has not appeared at the same hop distance h j in any of the earlier full traces to the AS,  then completes the trace, otherwise does not complete the trace. CHELEBY Intra –monitor redundancy

CHELEBY - Intra-Monitor Redundancy AS 1 B C A D E F G H Start the trace from 4 th hop (D)

 A destination IP is probed by only one monitor (Vantage Point) of a team  Vantage Points in the same area are geographically close  Their contribution to identify a new link/node is small  Identify ingress points of ASes to dynamically establish teams for each destination AS  One vantage point probing through each ingress point of an AS CHELEBY Inter –monitor redundancy

CHELEBY - Inter-Monitor Redundancy V A 1 V A 2 V B 1 V B 2 V B 3 D Area A Area B

 By Guillermo Baltra, Robert Beverly, Geoffrey G. Xie  A new interface-level network mapping technique  Underlying IPS  is the observation that a target AS is multi-homed and multi-connected INGRESS POINT SPREADING (IPS)

 An AS being connected to two or more separate ISPs (more than one AS).  If one outgoing link fails, outgoing traffic will automatically be routed via one of the remaining links.  Has multiple ingress points AS Multi-homing

 If probes enter the AS (multihomed) via different ingress points  Not only reduce the probing overhead but likely to reveal more of the target network’s topological structure D1D1 D3D3 D2D2 V2V2 V1V1 V3V3 A Multi-Homed AS INGRESS POINT SPREADING (IPS)

 1. Infer the number of ingress points for a target network  2. Select the VP with the highest likelihood to traverse an ingress point that has not yet been covered  3. To infer potential ingress points:  Subnet Centric Probing  IPS algorithm computes a per-destination network rank- ordered list of VPs based on prior rounds of probing. INGRESS POINT SPREADING (IPS)

 IPS seeks to utilize all of the ingress points discovered in prior rounds of probing  future probing can induce probe traffic to flow through each of these known ingresses  explore more of the destination network’s topology INGRESS POINT SPREADING (IPS)

 Uses one day’s worth of prior probing results to infer potential ingress points at different notional network boundaries for each target prefix  Use the knowledge of how networks are subnetted to select addresses to probe within each BGP advertised prefix  Adapt the number of probes to the degree of subnetting within the prefix to avoid wasted probing Subnet Centric Probing

Reducing the probing redundancy by - Generalizes DoubleTree without parametrization -Intelligently tuning (via TTL) the set of hops each trace interrogates -Start a trace with a TTL suitable to reach the destination and iteratively decrement the TTL until a previously discovered hop (i.e. at the AS ingress) is found. - Discover AS ingress points and paths to the AS via multiple vantage points AS ingress

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