Network Problem Diagnosis for Non-networkers

Network Problem Diagnosis for Non-networkers Les Cottrell – SLAC University of Helwan / Egypt, Sept 18 – Oct 3, 2010 Partially funded by DOE/MICS Field Work Proposal on Internet End-to-end Performance Monitoring (IEPM), also supported by IUPAP

Overview Goal: provide a practical guide to debugging common problems • Why is diagnosis difficult yet important? • Local host • Ping, Traceroute, PingRoute • Looking at time series • Locating bottlenecks • Correlation of problems with routes • More tools and problems • Where is a node • Who do you tell, what do you say? • Case studies and More Information

Why is diagnosis difficult? • Internet's evolution as a composition of independently developed and deployed protocols, technologies, and core applications • Diversity, highly unpredictable, hard to find “invariants” • Rapid evolution & change, no equilibrium so far • Findings may be out of date • Measurement/diagnosis not high on vendors list of priorities • Resources/skill focus on more interesting an profitable issues • Tools lacking or inadequate • Implementations are flaky & not fully tested with new releases

Add to that … • Distributed systems are very hard • A distributed system is one in which I can't get my work done because a computer I've never heard of has failed. Butler Lampson • Network is deliberately transparent • The bottlenecks can be in any of the following components: • the applications • the OS • the disks, NICs, bus, memory, etc. on sender or receiver • the network switches and routers, and so on • Problems may not be logical • Most problems are operator errors, configurations, bugs • When building distributed systems, we often observe unexpectedly low performance • the reasons for which are usually not obvious • Just when you think you’ve cracked it, in steps security • Firewall, NAT boxes etc. • Block pings, traceroute looks like port scan, diagnostic tool ports are blocked … • ISPs worried about providing access to core, making results public, & privacy issues

Sources of problems • Host “errors” • TCP buffers, heavy utilization … • Ethernet duplex and speed mismatch between your host and the network device • Misconfigured router/switches • Including routing errors, especially for backup paths • Bad equipment, wiring/fiber problem • Congestion

First steps • Command prompt, find out about network connection • ipconfig ? • ipconfig • Default gives IP address, gateway/1st router, subnet mask of all your network devices (Ethernet, wireless, bluetooth…) • Make a note of the gateway • Icon at bottom right of screen • Allows asking of questions and tries to provide assistance • Go to Command prompt and type • ping ?

Ping on Windows RTT Size of packet C:\Users\cottrell>ping –n 4 –l 32 mail.alex.edu.ca Pinging mail.alex.edu.ca [67.215.65.132] with 32 bytes of data: Reply from 67.215.65.132: bytes=32 time=80ms TTL=45 Reply from 67.215.65.132: bytes=32 time=85ms TTL=45 Reply from 67.215.65.132: bytes=32 time=83ms TTL=45 Reply from 67.215.65.132: bytes=32 time=90ms TTL=43 Ping statistics for 67.215.65.132: Packets: Sent = 4, Received = 4, Lost = 0 (0% loss), Approximate round trip times in milli-seconds: Minimum = 80ms, Maximum = 90ms, Average = 84ms IP address of target target Specify number pings ? Try: ping –t, what use is ping -f

C:\Users\cottrell>ping www.lbl.gov Pinging www.lbl.gov [128.3.41.105] with 32 bytes of data: Request timed out. Request timed out. Request timed out. Request timed out. Ping statistics for 128.3.41.105: Packets: Sent = 4, Received = 0, Lost = 4 (100% loss), Enable Telnet by following these steps: Start=>Control Panel=>Programs And Features=> Turn Windows features on or off=> Check Telnet Client Hit OK Now try: 16cottrell@pinger:~>telnet www.lbl.gov 80 Blank screen web server waiting to talk to you Hit ctrl ] and type exit Compare with another port (non existent application) C:\Users\cottrell>telnet www.lbl.gov 1010 Connecting To www.lbl.gov...Could not open connection to the host, on port 1010: Connect failed C:\Users\cottrell> Anomalies Pings blocked

Diversion on ports • Applications such as telnet (23), ssh (22) www (80, 443), DNS are assigned a “port” on the host • Sometimes written as for example www.slac.stanford.edu:80 • See http://www.iana.org/assignments/port-numbers for what applications use which ports

Try: • ping localhost • ping mail.alex.edu.eg • ping sohag-univ.edu.eg • ping www.minia.edu.eg • ping www.alex.edu.eg

3rd party ping (via Looking Glass) • Find servers: • http://www.cogentco.com/us/network_lookingglass.php, • http://www.ip.tiscali.net/lg/ • http://stat.qwest.net/cgi-bin/jlg-new-asia.pl • http://www.slac.stanford.edu/comp/net/wan-mon/viper/tulip_map.htm

RTT from California to world Europe E. Coast Brazil E. Coast US W. Coast US 300ms RTT (ms) Europe & S. America 0.3*0.6c Longitude (degrees) 300ms Frequency Source = Palo Alto CA, W. Coast RTT (ms.) Data from CAIDA Skitter project

Geostationary Satellite links Each bar represents min RTT for 1 country Satellite flies 24k miles high, RTT~400ms Note cut off between satellite and terrestrial Satellite 500 400 300 Terrestrial Min RTT (ms) 200 100 0 Country

Traceroute Rough algorithm Rough traceroute algorithm ttl=1; #To 1st router port=33434; #Starting UDP port max=30; #default maximum number of hops while hops <= maxhops & ttl<max { send UDP packet to host:port with ttl get response if time exceeded note roundtrip time else if UDP port unreachable print * next print output ttl++; port++ }

Traceroute (tracert on Windows) C:\Users\cottrell>tracert gets help C:\Users\cottrell>tracert-h 30 mail.alex.edu.eg Tracing route to mail.alex.edu.eg [193.227.16.29] over a maximum of 30 hops • 1 ms 1 ms 1 ms 10.13.11.1 2 1 ms <1 ms 1 ms 10.100.100.53 • 1 ms <1 ms <1 ms 10.0.0.3 • 1 ms 1 ms 1 ms 81.21.100.177 5 53 ms 12 ms 1 ms 10.181.28.33 6 2 ms 24 ms 2 ms 172.18.28.117 7 5 ms 6 ms 6 ms 172.20.1.162 8 6 ms 6 ms 8 ms 172.19.8.106 9 * * * 10 6 ms 6 ms 6 ms mail.alex.edu.eg [193.227.16.29] Try tracertwww.lbl.gov Why do the first hops take so long to reply? Try tracert –d www.lbl.gov Target IP address Max hops 3 RTTs Router IP address No response

Private address space • N.b. first few addresses are 10.x.y.z • Typically these are private (not known to the global Internet) IP addresses, that can be re-used at multiple sites • See http://en.wikipedia.org/wiki/Private_network • Ranges 10.0.0.0 – 10.255.255.255 (16M addresses, 24bits) • 172.16.0.0 – 172.31.255.255 (1M addresses, 20 bits) • 192.168.0.0 – 192.168.255.255 (65K addresses, 16 bits)

Traceroute from elsewhere • Traceroute to remote host • Is the route direct, over commercial congested nets • Reverse traceroute from remote host to you or 3rd party • www.slac.stanford.edu/comp/net/wan-mon/traceroute-srv.html • www.tracert.com/ • visualroute.visualware.com/ # requires Java Visualroute servers in Europe

Traceroute server results • Example: www.slac.stanford.edu/cgi-bin/nph-traceroute.pl Related info Security warning Traceroute Enter IP address or name Your IP address Your IP name

Warning • Some Linux versions have bug that incorrectly IDs cksum error on MPLS links. Make Pkt length>=140, else get checksum errors (not a problem, just annoying). e.g. on Linux • traceroutewww.slac.stanford.edu 140

Pingroute example Start of losses? • May help tell where losses start • Will need many pings if losses small But? Start of sustained losses Routers may not respond

Matt’s Traceroute (mtr) • Run traceroute, then ping each router n times • helps identify where in route the problems start to occur • Routers may not respond to pings, or may treat pings directed at them, differently to other packets • Get Matt’s TraceRoute MTR from www.bitwizard.nl/mtr/ or pathping (built into windows but inferior) • Slower • Less info

Pathpingen.wikipedia.org/wiki/PathPing Tracing route to mail.alex.edu.eg [193.227.16.29] over max 30 hops: 0 CDIV-PC83982.win.slac.stanford.edu [10.13.250.215] 1 10.13.11.1 2 10.100.100.53 3 10.0.0.3 4 81.21.100.177 5 10.181.28.33 6 172.18.28.117 7 172.20.1.162 8 172.19.8.106 9 10.191.8.30 10 mail.alex.edu.eg [193.227.16.29] Computing statistics for 250 seconds... Source to Here This Node/Link Hop RTT Lost/Sent = Pct Lost/Sent = Pct Address 0 CDIV-PC83982.win.slac.stanford.edu [10.13.250.215] 0/ 100 = 0% | 1 1ms 0/ 100 = 0% 0/ 100 = 0% 10.13.11.1 0/ 100 = 0% | 2 1ms 0/ 100 = 0% 0/ 100 = 0% 10.100.100.53 0/ 100 = 0% | 3 0ms 0/ 100 = 0% 0/ 100 = 0% 10.0.0.3 0/ 100 = 0% | 4 2ms 0/ 100 = 0% 0/ 100 = 0% 81.21.100.177 13/ 100 = 13% | 5 --- 100/ 100 =100% 87/ 100 = 87% 10.181.28.33 0/ 100 = 0% | 6 --- 100/ 100 =100% 87/ 100 = 87% 172.18.28.117 0/ 100 = 0% | 7 --- 100/ 100 =100% 87/ 100 = 87% 172.20.1.162 0/ 100 = 0% | 8 --- 100/ 100 =100% 87/ 100 = 87% 172.19.8.106 0/ 100 = 0% | 9 --- 100/ 100 =100% 87/ 100 = 87% 10.191.8.30 0/ 100 = 0% | 10 10ms 13/ 100 = 13% 0/ 100 = 0% mail.alex.edu.eg [193.227.16.29] Trace complete. Default probes/hop = 100 |=Link Router No RTT variance provided Help try pathping

Look at time series • Look at history plots (PingER, ISPs, own border router etc.), when did problem start, how big an effect is it? • Assumes you know “proximity” of paths for which there are archived active measurements to the path that you are interested in • Also that relevant measurements exist • www-iepm.slac.stanford.edu/pinger/ • Collaboration between Internet2/ESnet/Geant to provide access to router measurements holds promise

Example time series • Look for change in measured value • Note time • Correlate Italy disconnected

Moving towards application • Is the server application listening: • telnet www.slac.stanford.edu 80 • Trying 134.79.18.188... • Connected to www.slac.stanford.edu. • Escape character is '^]'. • ^] • telnet> quit • Connection closed. • Try user application (mem to mem & disk to disk) • GridFTP, bbcp, bbftp … • Iperf or thrulay (also provides RTT) to test TCP or UDP throughput • dast.nlanr.net/Projects/Iperf/, www.internet2.edu/~shalunov/thrulay/ • NDT (http://www.internet2.edu/performance/ndt/) • What are the interface speeds?, What is the bottleneck? • Is there a duplex mismatch?’ Are buffers set right (both ends)?

NDT example Try: http://netspeed.stanford.edu/

And then … • Wireless • Avoid peer-to-peer/ad-hoc connections • Disable connecting to ad-hoc (set infrastructure only) • Disable bridging • How to do it varies by OS (XP, OSX, Linux) • Ad hoc can still interfere if on same channel • Tools to locate an access point (e.g. Yellow-Jacket) • See • www2.slac.stanford.edu/comp/net/wireless/Wireless-Meeting-Handout.mht • NAT boxes may block or not support application • Private addresses: • 10.0.0.0 - 10.255.255.255 a single class A net • 172.16.0.0 - 172.31.255.255 16 contiguous class Bs • 192.168.0.0 – 192.168.255.255 256 contiguous class Cs

Strategy: divide & conquer • Ping to localhost, ping to gateway & to remote host • Use IP address to avoid nameserver problems • Look for connectivity, loss & RTT • May need to run for a long time to see some pathologies (e.g. bursty loss dues to DSL loss of sync) • Use telnet host port to see if ping blocked • Traceroute to remote host • Reverse traceroute from remote host to you • Ping routers along route (mtr helps) • Look at history plots (PingER), when did problem start, how big an effect is it? • Look at own connectivity NDT (netspeed.stanford.edu)

“Where is” a host? • Beware some of information following is ephemeral, in general use heuristics with Google • Google “Internet country codes” for TLDs • Host may not be in TLD country, especially developing regions often use proxies elsewhere • Location may be encoded in router name • ipls=Indianapolis, snv=Sunnyvale … • Name server lookup (nslookup & dig) to find hostname given IP address 47cottrell@netflow:~>nslookup 210.56.16.10 Server: localhost Address: 127.0.0.1 Name: lhr.comsats.net.pk Address: 210.56.16.10 • Use a whoisserver (download www.gena01.com/win32whois/) • www.networksolutions.com/cgi-bin/whois/whois (Americas & Africa) • www.ripe.net/cgi-bin/whois (Europe) • www.apnic.net/ (Asia) • May identify site name, address, contact, etc, not all domains are in databases (e.g. will not find comsats.net.pk)

“Where is” a host – cont. • Find the Autonomous System (AS) administering • Form giving AS for domain name • http://www.fixedorbit.com/search.htm • Gives AS number, name adjacent AS’s web page for AS • Given an AS find out more about it: • Use http://bgp.potaroo.net/cidr/ go to bottom and enter AS into form: • Gives ISP name, web page, phone number, email, hours etc. • Review list of AS's ordered by Upstream AS Adjacency • www.telstra.net/ops/bgp/bgp-as-upsstm.txt • Tells what AS is upstream of an ISP

“Where is” a host - cont. • Visit site’s www server, often location in home page • May be able to get lat & long form database: • www.geoiptool.com/ or via: geotool.flagfox.net/ • http://www.hostip.info/index.html • Networldmap determines geographical information by acquiring location information from willing participants. • http://www.ip2location.com/ • But it is a subscriber service ($$$, but …), however it is probably best for developing regions • Quova has a large (2.4 Billion addresses) database of IP addresses to locations that they can provide access to for organizations, but must subscribe ($$$). • Triangulate pings from landmarks: • www.slac.stanford.edu/grp/scs/net/talk10/geolocation.pptx

Who you gonna tell? • Local network support people • Internet Service Provider (ISP) usually done by local networker • Usually will know immediate one, e.g. trouble@es.net • Use puck.nether.net/netops/nocs.cgi to find ISP • Use www.telstra.net/ops/bgp/bgp-as-upsstm.txt to find upstream ISPs • Well managed sites and ISPs maintain a list of email addresses such as abuse@ or postmaster@, that one can send email to, for example to complain about spam etc. • This follows an Internet recommendation (RFC 2142). • Some less helpful sites do not provide such services, for more on these, see RFC-ignorant.org

What ya gonna tell ‘em? • Describe problem with details • What is affected? • Application, host OS (uname –a), NIC (ifconfig, route) • How is it affected? • Non responsiveness, unable to contact remote host • Slow performance (see Brian’s talk), packet loss • When did it start? • Send ping output between hosts • Send traceroute forward & reverse – if possible • Maybe use –I (ICMP option) • NDT • Identify when it started • If complex think about creating web page with details • Top, vmstat, pingroute, pipechar, application output (GridFTP, iperf)…

More Information • Tutorial on monitoring • www.slac.stanford.edu/comp/net/wan-mon/tutorial.html • RFC 2151 on Internet tools • www.freesoft.org/CIE/RFC/Orig/rfc2151.txt • Network monitoring tools • www.slac.stanford.edu/xorg/nmtf/nmtf-tools.html • www.caida.org/tools/taxonomy/ • Network Performance Tools: an I2 Cookbook • e2epi.internet2.edu/network-perf-wk/tools-cookbook.pdf • Case Studies: • confluence.slac.stanford.edu/display/IEPM/Problem+Cases • e2epi.internet2.edu/case-studies/

More slides

Local Host (also see NDT later) • Usual Unix tools (uname -a, top, vmstat, iostat ..) • Is the host overloaded, do you have a gateway (route), name server (nslookup), which interface are you using (mii-tool (needs root), gives duplex & speed = common error source) • Net:ifconfig –a (look at errors),netstat –a • Is server running (if you know port)? • >telnet localhost 2811 Trying 127.0.0.1 • 220 aftpexp04.bnl.gov GridFTP Server 1.12 GSSAPI type Globus/GSI wu-2.6.2 (gcc32dbg, 1069715860-42) ready. • ^] • telnet> quit

Ping example Packet size Remote host Repeat count RTT syrup:/home$ ping -c 6 -s 64 thumper.bellcore.com PING thumper.bellcore.com (128.96.41.1): 64 data bytes 72 bytes from 128.96.41.1: icmp_seq=0 ttl=240 time=641.8 ms 72 bytes from 128.96.41.1: icmp_seq=2 ttl=240 time=1072.7 ms 72 bytes from 128.96.41.1: icmp_seq=3 ttl=240 time=1447.4 ms 72 bytes from 128.96.41.1: icmp_seq=4 ttl=240 time=758.5 ms 72 bytes from 128.96.41.1: icmp_seq=5 ttl=240 time=482.1 ms --- thumper.bellcore.com ping statistics --- 6 packets transmitted, 5 packets received, 16% packet loss round-trip min/avg/max = 482.1/880.5/1447.4 ms Missing seq # Summary

Traceroute Remote host Max hops (20) Probes/hop • UDP/ICMP tool to show route packets take from local to remote host 17cottrell@flora06:~>traceroute -q 1 -m 20 lhr.comsats.net.pk traceroute to lhr.comsats.net.pk (210.56.16.10), 20 hops max, 40 byte packets 1 RTR-CORE1.SLAC.Stanford.EDU (134.79.19.2) 0.642 ms 2 RTR-MSFC-DMZ.SLAC.Stanford.EDU (134.79.135.21) 0.616 ms 3 ESNET-A-GATEWAY.SLAC.Stanford.EDU (192.68.191.66) 0.716 ms 4 snv-slac.es.net (134.55.208.30) 1.377 ms 5 nyc-snv.es.net (134.55.205.22) 75.536 ms 6 nynap-nyc.es.net (134.55.208.146) 80.629 ms 7 gin-nyy-bbl.teleglobe.net (192.157.69.33) 154.742 ms 8 if-1-0-1.bb5.NewYork.Teleglobe.net (207.45.223.5) 137.403 ms 9 if-12-0-0.bb6.NewYork.Teleglobe.net (207.45.221.72) 135.850 ms 10 207.45.205.18 (207.45.205.18) 128.648 ms 11 210.56.31.94 (210.56.31.94) 762.150 ms 12 islamabad-gw2.comsats.net.pk (210.56.8.4) 751.851 ms 13 * 14 lhr.comsats.net.pk (210.56.16.10) 827.301 ms location Long delay satellite No response: Lost packet or router ignores

Pingroute • Ping routers along route, e.g. a tool to install that helps: • www.slac.stanford.edu/comp/net/fpingroute.pl • or www.slac.stanford.edu/comp/net/fpingroute.pl if fpingavaialable 15cottrell@noric04:~>fpingroute.pl fpingroute.pl does a traceroute to the selected host. For each of the hops along the route it then uses fping to ping each node (in parallel) 'count' times. Output includes traceroute information, RTTs, losses for 100 and 'size‘ byte pings. Version=0.21, 8/24/04 Usage: fpingroute.pl [Opts] host where host is the remote host's IP address or name e.g. www.slac.stanford.edu Opts: [-c count default=10] [-s size default=1400] [-i initial default=1] Example: fpingroute.pl -i 3 -c 10 -s 1400 www.triumf.ca

Other tools • Ntop • Summarizes libpcap (sniffer) infor • Internet2 Detective: • Tests connectivity to I2, bandwidth, multicast, IPv6 • Can run as Java applet • http://detective.internet2.edu/ • NLANR Internet Advisor • Ethereal, tcpdump, snoop for masochists • Passive tools: • Netflow for characterizing network, spotting abnormalities, e.g. • www.itec.oar.net/abilene-netflow • www.slac.stanford.edu/comp/net/slac-netflow/html/SLAC-netflow.html • SNMP based tools

Network Problem Diagnosis for Non-networkers