Http://sdu.ictp.it/lowbandwidth/ Diagnostic Steps Les Cottrell – SLAC Presented at the...

http://sdu.ictp.it/lowbandwidth/

Diagnostic Steps

Les Cottrell – SLACPresented at the Optimization Technologies for Low-Bandwidth Networks, ICTP

Workshop, Trieste, Italy, 9-20 October 2006 http://www.slac.stanford.edu/grp/scs/net/talk06/diagnostics.ppt

Partially funded by DOE/MICS Field Work Proposal on Internet End-to-end Performance Monitoring (IEPM), also supported by IUPAP

Slide: 2Les Cottrell, SLAC

Get ready

Bring up terminal window so can try some commands Bring up the presentation so can click on links:

www.slac.stanford.edu/grp/scs/net/talk06/diagnostics.ppt


AimGoal: 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Findings may be out of date Measurement/diagnosis not high on vendors list of priorities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 …

Duplex mismatch (Ethernet) Misconfigured router/switches

Including routing errors, especially for backup paths

Bad equipment, wiring/fiber problem Congestion


Fire: Local Host

Usual Unix tools (uname-a, top, vmstat, iostat …) Is the host overloaded, do you have a gateway (route), name

server (nslookup/dig), which interface are you using (mii-tool (needs root), gives duplex & speed = common error source)21cottrell@pinger:~>sudo mii-tool eth0

– eth0: 100 Mbit, full duplex, link ok

Net: ifconfig –a (look at errors), netstat –a | more

Is server running (if you know port)? >telnet localhost 2811

Trying 127.0.0.1220 aftpexp04.bnl.gov GridFTP Server 1.12 GSSAPI type

Globus/GSI wu-2.6.2 (gcc32dbg, 1069715860-42) ready.^]telnet> quit


Ping Ping 1. to localhost, 2. ping to gateway (use route or traceroute to find

gateway), 3. ping to well known host 4. & to relevant remote host

Use IP address to avoid nameserver problems Look for connectivity, loss, RTT, jitter, dups May need to run for a long time to see some pathologies

(e.g. bursty loss due to DSL loss of sync) Try flood pings if suspect rate limited Use synack or sting if ICMP blocked

www-iepm.slac.stanford.edu/tools/synack/


Ping example

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

Repeat count Packet size Remote host

RTT

Missing seq #

Summary


Try the following Ping Examplesping cepheid.physics.utoronto.ca

From mcl-gpb.gw.utoronto.ca … Destination Host Unreachable

ping rolandlap.ph.unimelb.edu.auFrom rtr4-000037.unimelb.edu.au … Packet filtered

ping www.ncit.edu.npping: unknown host www.ncit.edu.np

ping inpe-gw-sp.cptec.inpe.brFrom 150.163.200.100 icmp_seq=0 Time to live exceeded

ping www.ug.edu.gh34 packets transmitted, 0 received, 100% packet loss, time 33068ms

synack -p 80 -k 5 www.ug.edu.gh5 packets transmitted, 5 packets received, 0.00 percent packet lossround-trip (ms) min/avg/max = 182.052/182.701/183.151 (std = 0.578) (median = 183.095) (interquartile range = 1.039) (25 percentile = 182.085) (75 percentile = 183.124)


3rd party ping Find servers:

http://www.slac.stanford.edu/comp/net/wan-mon/traceroute-srv.html Glasgow University*# Scotland. ICTP +*, Trieste, Italy. IHEP + Beijing, China.

Modify URL to request a ping for hosts with +pinger.ictp.it/cgi-bin/traceroute.pl?

function=ping&target=brunsvigia.tenet.ac.zaping from 134.79.18.163 (www.slac.stanford.edu) to

196.21.99.222 (brunsvigia.tenet.ac.za) for 140.105.16.64

– PING 196.21.99.222: 56 data bytes– 64 bytes from brunsvigia.tenet.ac.za (196.21.99.222): icmp_seq=0. time=370. ms – 64 bytes from brunsvigia.tenet.ac.za (196.21.99.222): icmp_seq=1. time=1911. ms – 64 bytes from brunsvigia.tenet.ac.za (196.21.99.222): icmp_seq=2. time=911. ms 64 bytes

from brunsvigia.tenet.ac.za (196.21.99.222): icmp_seq=3. time=385. ms – 64 bytes from brunsvigia.tenet.ac.za (196.21.99.222): icmp_seq=4. time=366. ms – ----196.21.99.222 PING Statistics---- 5 packets transmitted, 5 packets received, 0% packet

loss round-trip (ms) min/avg/max = 366/788/1911


RTT from California to world

Longitude (degrees)

300ms

300ms

RTT (ms.)

Fre

quen

cy

RT

T (

ms)

Source = Palo Alto CA, W. Coast

E. C

oast

US

W. C

oast

US

Eur

ope

& S

. Am

eric

a

Europe

0.3*0.6c

Bra

zil

E. C

oast

Data from CAIDA Skitter project


Traceroute 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.ht

ml www.tracert.com/

CAIDA Mouse sensitivemap


Traceroute

UDP/ICMP tool to show route packets take from local to remote host

17cottrell@flora06:~>traceroute -q 1 -m 20 lhr.comsats.net.pktraceroute 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 ms10 207.45.205.18 (207.45.205.18) 128.648 ms11 210.56.31.94 (210.56.31.94) 762.150 ms12 islamabad-gw2.comsats.net.pk (210.56.8.4) 751.851 ms13 * 14 lhr.comsats.net.pk (210.56.16.10) 827.301 ms

Probes/hop Max hops Remote host

No response:Lost packet or router

ignores

Long delaysatellite

location


Traceroute server results Example: www.slac.stanford.edu/cgi-bin/nph-traceroute.pl

Securitywarning

Traceroute

Relatedinfo

Enter IP address or name


Graphical Traceroute http://visualroute.visualware.com/


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/pingroute.pl if fping N/A

15cottrell@noric04:~>fpingroute.plfpingroute.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, 8/24/04Usage: 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


Pingroute example May help tell where losses start Will need many pings if losses small

Routers may not

respond

Start of losses?

But?

Start ofsustained

losses


Look at time series Look at history plots (PingER, IEPM-BW, 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 existwww-iepm.slac.stanford.edu/pinger/ amp.nlanr.net/ unfortunately no longer fundedISPs plots:

(www.slac.stanford.edu/comp/net/wan-mon/netmon.html for a a place to start looking)

– Abilene: http://stryper.uits.iu.edu/abilene/ – GEANT: http://stats.geant.net/usagemap/usagemap– RIPE: http://www.ripe.net/projects/ttm/Plots/ – ESnet: http://measurement.es.net/ (OWAMP)

Collaboration between Internet2/ESnet/Geant to provide access to router measurements holds promise

Look at traceroute histories (see later)


Example time series

Look for change in measured value Note

time Correlate Italy disconnected


Find location of a bottleneck Look at hops along the path

Pingroute (see earlier) If possible look at utilizations or active probes launched from there Pathneck http://www.cs.cmu.edu/~hnn/pathneck/

Uses trains of packets to probe hops along route, looking at dispersion induced by queuing

Pipechar (son of pathchar, pchar) http://www.dsd.lbl.gov/OldProjects/NCSSend packets of varying sizes to each router along pathLook at RTT as a function of packet sizeFrom slope deduce “bandwidth”Diferentiate to find capacity at each hopHowever pipechar has uncertain supportPacket size variation limited to 1-MTU (~1500) Bytes, so on fast links

timing is difficult, with the result that estimates may not be reliable (OK for slow links)


Divide & Conquer

Abilene has hosts at major PoPs running bwctl So make measurements from end to middle to ID loss

of performance http://e2epi.internet2.edu/pipes/ami/bwctl/


Correlate with routes (traceanal)


Visualizing traceroutes www.slac.stanford.edu/comp/net/iepm-bw.slac.stanford.edu/

slac_wan_bw_tests.html, => traceroutes One compact page per day One row per host, one column per hour One character per traceroute to indicate pathology or change (usually

period(.) = no change) Identify unique routes with a number

Be able to inspect the route associated with a route number Provide for analysis of long term route evolutions

Route # at start of day, gives idea of route stability

Multiple route changes (due to GEANT), later restored to original route

Period (.) means no change


Changes in network topology (BGP) can result in dramatic changes in performance

Snapshot of traceroute summary table

Samples of traceroute trees generated from the table

ABwE measurement one/minute for 24 hours Thurs Oct 9 9:00am to Fri Oct 10 9:01am

Drop in performance(From original path: SLAC-CENIC-Caltech to SLAC-Esnet-LosNettos (100Mbps) -Caltech )

Back to original path

Changes detected by IEPM-Iperf and AbWE

Esnet-LosNettos segment in the path(100 Mbits/s)

Hour

Rem

ote

host

Dynamic BW capacity (DBC)

Cross-traffic (XT)

Available BW = (DBC-XT)

Mbit

s/s

Notes:1. Caltech misrouted via Los-Nettos 100Mbps commercial net 14:00-17:002. ESnet/GEANT working on routes from 2:00 to 14:003. A previous occurrence went un-noticed for 2 months4. Next step is to auto detect and notify

Los-Nettos (100Mbps)


Moving towards application Try user application (mem to mem & disk to disk)

GridFTP, bbcp, bbftp … Iperf or thrulay (also provides RTT) to test TCP or UDP

throughput (injects traffic, +server) dast.nlanr.net/Projects/Iperf/ www.internet2.edu/~shalunov/thrulay/

Available bandwidth: Pathload:

www-static.cc.gatech.edu/fac/Constantinos.Dovrolis/pathload.html Pathchirp: www.spin.rice.edu/Software/pathChirp/ bing …

NDT What are the interface speeds? What is the bottleneck? Is there a duplex mismatch? Are buffers set right (both ends)?

Bottleneck

Min spacingAt bottleneckSpacing preserved

On higher speed links


http://e2epi.internet2.edu/ndt/NDT example (Rich Carlson)


Other tools Ntop

Summarizes libpcap (sniffer) infor

Internet2 Detective: Tests connectivity to I2, bandwidth, multicast, IPv6

Can run as Java applethttp://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


And then … Wireless

Avoid peer-to-peer/ad-hoc connectionsDisable connecting to ad-hoc (set infrastructure only)Disable bridgingHow 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) Vendors have management tools to enable APs to detect rogue APs

NAT boxes may block or not support application Private addresses:

10.0.0.0 - 10.255.255.255 a single class A net172.16.0.0 - 172.31.255.255 16 contiguous class Bs192.168.0.0 – 192.168.255.255 256 contiguous class Cs


“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 to find hostname given IP address47cottrell@netflow:~>nslookup 210.56.16.10Server: localhostAddress: 127.0.0.1Name: lhr.comsats.net.pkAddress: 210.56.16.10

Use a whois server, e.g. 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.htmGives 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 Adjacencywww.telstra.net/ops/bgp/bgp-as-upsstm.txtTells what AS is upstream of an ISP


“Where is” a host - cont.

May be able to get latitude & longitude: http://www.hostip.info/index.html http://www.ip2location.com/

But it is a subscriber service ($$$, but …), however it is probably best for developing regions

Google:www.geoiptool.com/http://www.geoiptool.com/

Triangulate pings from landmarks (in development) http://www.slac.stanford.edu/comp/net/wan-mon/tulip/

Need more landmarks, send email [email protected]

http://www.cs.cornell.edu/~bwong/octant/ # for US only


Who you gonna tell?

Local network support people Internet Service Provider (ISP) usually done by local networker

Usually will know immediate one, e.g. [email protected] 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 hostSlow 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)…


Web page examples: Case studies

http://www.slac.stanford.edu/grp/scs/net/case/html/ http://e2epi.internet2.edu/case-studies/


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

Network Monitoring sites www.slac.stanford.edu/comp/net/wan-mon/netmon.html

How to Accelerate Your Internet, ISBN: 0-9778093-1-5, Ed. Flickenger R.


Local Host - LISA

Localhost Information Service Agent LISA is a Java Web Start application which provides: Integration with MonALISA Complete Monitoring of the System (Load, CPU, Memory, Disk,

Disk IO, Paging, Processes, Network Traffic and Connectivity...). History and instantaneous Filters to trigger actions when predefined conditions are detected. A user Friendly GUI to present the monitoring information. Optimization modules for distributed applications. It is a lightweight application that can be easily deployed on any

system. Modules for End to End network measurements ( e.g. IPERF). See monalisa.caltech.edu/dev_lisa.html

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