Network Diagnostic and Discovery with Traceroute Prepared and presented by PhD candidate,Yihua He

Roadmap Identifying the AS PATH Identifying the AS PATH Which AS a packet goes throughWhich AS a packet goes through Review of how traceroute works Review of how traceroute works Possible ways to do IP->AS Possible ways to do IP->AS Hands-on experience with BGP tables Hands-on experience with BGP tables What can traceroute tell us besides reachability? What can traceroute tell us besides reachability? Internet routes are not symmetric Internet routes are not symmetric

AS A AS B AS C AS D Autonomous System (AS) Autonomous System Forwarding Path Example: Pinpoint forwarding loop & responsible AS IP traffic Internet source destination

Border Gateway Protocol (BGP) BGP path may differ from forwarding AS path Routing loops and deflectionsRouting loops and deflections Route aggregation and filteringRoute aggregation and filtering BGP misconfigurationBGP misconfiguration AS A AS B AS C prefix d Signaling path: control traffic d: path=[C] Forwarding path: data traffic d: path=[BC] Origin AS d: path=[B C] d: path=[A B C]

Traceroute: Measuring the Forwarding Path Time-To-Live field in IP packet header Time-To-Live field in IP packet header Source sends a packet with a TTL of nSource sends a packet with a TTL of n Each router along the path decrements the TTLEach router along the path decrements the TTL “TTL exceeded” sent when TTL reaches 0“TTL exceeded” sent when TTL reaches 0 Traceroute tool exploits this TTL behavior Traceroute tool exploits this TTL behavior source destination TTL=1 Time exceeded TTL=2 Send packets with TTL=1, 2, 3, … and record source of “time exceeded” message

Traceroute gives IP-level forwarding path * * Traceroute output: (hop number, IP address, DNS name) Traceroute from Berkeley to ( ) inr-daedalus-0.CS.Berkeley.EDU soda-cr-1-1-soda-br-6-2 vlan242.inr-202-doecev.Berkeley.EDU gigE6-0-0.inr-666-doecev.Berkeley.EDU qsv-juniper--ucb-gw.calren2.net POS1-0.hsipaccess1.SanJose1.Level3.net ? pos8-0.hsa2.Atlanta2.Level3.net pop2-atm-P0-2.atdn.net ? pop1-atl-P4-0.atdn.net www4.cnn.com

Map Traceroute Hops to ASes * * Traceroute output: (hop number, IP) AS25 AS11423 AS3356 AS1668 AS5662 Berkeley CNN Calren Level3 AOL Need accurate IP-to-AS mappings (for network equipment).

Possible Ways to Get IP-to-AS Mapping(1) DNS names: DNS names: Inaccurate, and in a lot of times, Wrong!Inaccurate, and in a lot of times, Wrong! Anyone, with $5/year, can register a and point it to any IP address! Anyone, with $5/year, can register a and point it to any IP address! Some of the IPs do not have any DNS name.Some of the IPs do not have any DNS name. Routing address registry (WHOIS) Routing address registry (WHOIS) That’s what you did in Lab1That’s what you did in Lab1 More accurate. However…More accurate. However… Voluntary public registry such as whois.radb.netVoluntary public registry such as whois.radb.net Prone to human input errorsProne to human input errors Incomplete and maybe out-of-dateIncomplete and maybe out-of-date Mergers, acquisitions, delegation to customers Mergers, acquisitions, delegation to customers

Possible Ways to Get IP-to-AS Mapping (2) Origin AS in BGP paths Origin AS in BGP paths Prefix= /24, ASpath=[ ]Prefix= /24, ASpath=[ ] Public BGP routing tables such as RouteViewsPublic BGP routing tables such as RouteViewsRouteViews Almost real time and avoiding most human input errorsAlmost real time and avoiding most human input errors It’s approximately 98% accurate,It’s approximately 98% accurate, Multiple Origin ASes (MOAS) Multiple Origin ASes (MOAS) due to merge in a lot of casesdue to merge in a lot of cases E.g., around , /16 had two ASes announced its address block: AS5677 and AS7132. That was PacBell and SBCE.g., around , /16 had two ASes announced its address block: AS5677 and AS7132. That was PacBell and SBC Now AS5677 does not exist anymoreNow AS5677 does not exist anymore No mapping No mapping Some ASes intentionally do not want to advertise the route/IPsSome ASes intentionally do not want to advertise the route/IPs Incomplete viewIncomplete view

Hands-on Experience with BGP Routing Tables Telnet://route-views.routeviews.org Telnet://route-views.routeviews.org Telnet://route-views.routeviews.org Show ip bgp summaryShow ip bgp summary Whose BGP feeds do the router take? Whose BGP feeds do the router take? Show ip bgpShow ip bgp Prefix Prefix Origin AS Origin AS AS Path AS Path Collected at Collected at Other BGP table collections are: Other BGP table collections are:

What can traceroute tell us? Where are those routers? Where are those routers? from DNSfrom DNS City name City name Airport name Airport name From roundtrip timeFrom roundtrip time Light travels approximately 2*10^8 meters/sec in fiber cables Light travels approximately 2*10^8 meters/sec in fiber cables When non-congested, the major delay is propagation delay When non-congested, the major delay is propagation delay If you see a host with roundtrip time of 10ms, you know it must be within 600 miles radius. If you see a host with roundtrip time of 10ms, you know it must be within 600 miles radius. Theoretically, with multiple vantage point, you can pinpoint where the routers are. Theoretically, with multiple vantage point, you can pinpoint where the routers are.

Internet routes are not symmetric! Try traceroute from both ends Try traceroute from both ends And we’ll find most routes are not symmetric! And we’ll find most routes are not symmetric! Why? Why? Hot potato routing --- try to use other guys’ network as much as possibleHot potato routing --- try to use other guys’ network as much as possible Policy routing --- when multihomedPolicy routing --- when multihomed

Traceroute from other places Remote traceroute serversRemote traceroute servers Hundreds of themHundreds of them Limited probe rateLimited probe rate Not always availableNot always available skitter/ skitter/ skitter/ skitter/ Dedicated remote traceroute monitorsDedicated remote traceroute monitors Almost unlimited probe rateAlmost unlimited probe rate Only a couple of dozens of themOnly a couple of dozens of them

Any questions?