NFNN2, 20th-21st June 2005
National e-Science Centre, Edinburgh
Diagnostic Steps
Les Cottrell – SLAC
Presented at the Networks for Non Networkers 2nd International Workshop, 20-21 June
2005, Edinburgh, Scotland
http://www.slac.stanford.edu/grp/scs/net/talk05/nfnn2-jun05.ppt
Partially funded by DOE/MICS Field Work Proposal on Internet End-to-end
Performance Monitoring (IEPM), also supported by IUPAP
http://gridmon.dl.ac.uk/nfnn/
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
‹Where is a node
‹Who do you tell, what do you say?
‹Case studies and More Information
Les Cottrell, SLAC
Slide: 2
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„ Findings may be out of date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
Les Cottrell, SLAC
Slide: 3
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
z the reasons for which are usually not obvious
‹ Just when you think you’ve cracked it, in steps security
„ Block pings, traceroute looks like port scan, diagnostic tool ports are
blocked …
„ ISPs worried about providing access to core, making results public, &
privacy issues
Les Cottrell, SLAC
Slide: 4
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), also provides duplex & speed common error source)
„ Net: ifconfig –a (look at errors), netstat –a
‹ 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
Les Cottrell, SLAC
Slide: 5
Ping
‹Ping to localhost, ping to gateway, ping to well
known host & 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)
„ Use synack or sting if ICMP blocked
zwww-iepm.slac.stanford.edu/tools/synack/
Les Cottrell, SLAC
Slide: 6
Ping example
Repeat count
Packet size
Remote host
RTT
syrup:/home$ ping -c 6 -s 64 thumper.bellcore.com
PING thumper.bellcore.com (128.96.41.1): 64 data bytes
Missing seq #
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
Summary
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
Les Cottrell, SLAC
Slide: 7
3rd party ping (via Looking Glass)
‹ Find servers:
„ www.caida.org/analysis/routing/reversetrace/
‹ Example: http://stats.geant.net/cgi-bin/lg/lg.cgi
„ Ok for checking connectivity and RTT but not for losses (unless
huge)
Looking Glass Results - ch1.ch.geant.net
Date: Mon May 30 21:28:39 2005 GMT
Query: Ping <IP_Addr | FQDN>Real Query: ping rapid count 5
Argument(s): www.slac.stanford.edu
PING www8.slac.stanford.edu (134.79.18.163): 56 data bytes
!!!!!
--- www8.slac.stanford.edu ping statistics --5 packets transmitted, 5 packets received, 0% packet loss round-trip
min/avg/max/stddev=167.316/172.212/191.222/9.506 ms
Les Cottrell, SLAC
Slide: 8
Traceroute
‹Traceroute to remote host
‹Reverse traceroute from remote host to you or 3rd
party
„ www.slac.stanford.edu/comp/net/wan-mon/traceroutesrv.html
„ www.tracert.com/
„ www.caida.org/analysis/routing/reversetrace/
CAIDA
Mouse
sensitive
map
Les Cottrell, SLAC
Slide: 9
Traceroute
Probes/hop
Max hops
Remote host
‹ UDP/ICMP tool to show route packets take from local to
remote host
location
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
Long delay
6 nynap-nyc.es.net (134.55.208.146) 80.629 ms
satellite
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
No response:
10 207.45.205.18 (207.45.205.18) 128.648 ms
Lost packet or router
11 210.56.31.94 (210.56.31.94) 762.150 ms
ignores
12 islamabad-gw2.comsats.net.pk (210.56.8.4) 751.851 ms
13 *
Les
SLAC
Slide: 10
14Cottrell,
lhr.comsats.net.pk
(210.56.16.10) 827.301 ms
Brazil
300ms
E. Coast
E. Coast US
Europe & S. America
RTT (ms)
Frequency
W. Coast US
RTT from California to world
Europe
0.3*0.6c
300ms
Longitude (degrees)
Source = Palo Alto CA, W. Coast
RTT (ms.)
Les Cottrell, SLAC
Data from CAIDA Skitter
project
Slide:
11
Traceroute server results
‹ Example: www.slac.stanford.edu/cgi-bin/nph-traceroute.pl
Related
info
Security
warning
Traceroute
Enter IP address or name
Les Cottrell, SLAC
Slide: 12
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 fping N/A
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
Les Cottrell, SLAC
Slide: 13
Pingroute example
‹May help tell where losses start
‹Will need many pings if losses small
Start of losses?
But?
Start of
sustained
losses
Les Cottrell, SLAC
Routers
may
not
respond
Slide: 14
Look at time series
‹Look at history plots (PingER, AMP, 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 exist
zwww-iepm.slac.stanford.edu/pinger/
zamp.nlanr.net/
zISPs plots:
–
–
–
–
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)
Les Cottrell, SLAC
Slide: 15
Example time series
‹Look for
change in
measured
value
„ Note
time
„ Correlate
Les Cottrell, SLAC
Italy disconnected
Slide: 16
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
„ Pipechar (son of pathchar, pchar)
zSend packets of varying sizes to each router along path
zLook at RTT as a function of packet size
zFrom slope deduce “bandwidth”
zDiferentiate to find capacity at each hop
zHowever pchar is no longer supported, pathchar is very
slow, pipechar has uncertain support (ask Brian)
zPacket size variation limited to 1-MTU (~1500) Bytes, so
on fast links timing is difficult, with the result that
estimates may not be reliable
– Find pipechar at: http://www.dsd.lbl.gov/OldProjects/NCS/
Les Cottrell, SLAC
Slide: 17
Correlate with routes (traceanal)
Les Cottrell, SLAC
Slide: 18
Visualizing 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
Les Cottrell, SLAC
Slide: 19
Pathology Encodings
Probe type
Change but same AS
No change
Change in only 4th octet
End host not pingable
Hop does not respond
Multihomed
ICMP checksum
Stutter
! Annotation (!X)
Les Cottrell, SLAC
Slide: 20
Navigation
traceroute to CCSVSN04.IN2P3.FR (134.158.104.199), 30 hops max, 38 byte packets
1 rtr-gsr-test (134.79.243.1) 0.102 ms
…
13 in2p3-lyon.cssi.renater.fr (193.51.181.6) 154.063 ms !X
#rt#
0
1
2
3
4
5
6
7
8
Les Cottrell, SLAC
firstseen
1086844945
1087467754
1087472550
1087529551
1087875771
1087957378
1088221368
1089217384
1089294790
lastseen
1089705757
1089702792
1087473162
1087954977
1087955566
1087957378
1088221368
1089615761
1089432163
route
...,192.68.191.83,137.164.23.41,137.164.22.37,...,131.215.xxx.xxx
...,192.68.191.83,171.64.1.132,137,...,131.215.xxx.xxx
...,192.68.191.83,137.164.23.41,137.164.22.37,...,131.215.xxx.xxx
...,192.68.191.83,137.164.23.41,137.164.22.37,...,131.215.xxx.xxx
...,192.68.191.83,137.164.23.41,137.164.22.37,...,(n/a),131.215.xxx.xxx
...,192.68.191.83,137.164.23.41,137.164.22.37,...,131.215.xxx.xxx
...,192.68.191.146,134.55.209.1,134.55.209.6,...,131.215.xxx.xxx
...,192.68.191.83,137.164.23.41,(n/a),...,131.215.xxx.xxx
...,192.68.191.83,137.164.23.41,137.164.22.37,(n/a),...,131.215.xxx.xxx
Slide: 21
History Channel
Les Cottrell, SLAC
Slide: 22
AS’ information
Les Cottrell, SLAC
Slide: 23
Changes in network topology (BGP) can result
in dramatic changes in performance
Remote host
Hour
ps)
00Mb
1
(
s
o
ett
Los-N
Samples of
traceroute trees
generated from the
table
Snapshot of traceroute summary table
Mbits/s
Notes:
1. Caltech misrouted via Los-Nettos 100Mbps commercial net 14:00-17:00
2. ESnet/GEANT working on routes from 2:00 to 14:00
3. A previous occurrence went un-noticed for 2 months
4. Next step is to auto detect and notify
Drop in performance
Back to original path
Dynamic BW capacity (DBC)
(From original path: SLAC-CENIC-Caltech
to SLAC-Esnet-LosNettos (100Mbps) -Caltech )
Changes detected by
IEPM-Iperf and AbWE
Available BW = (DBC-XT)
Cross-traffic (XT)
Esnet-LosNettos segment in the path
(100 Mbits/s)
measurement
LesABwE
Cottrell,
SLACone/minute for 24 hours Thurs Oct 9 9:00am to Fri Oct 10 9:01am
Slide: 24
Moving towards application
‹See Brian’s talk
‹Try user application (mem to mem & disk to disk)
„ GridFTP, bbcp, bbftp …
‹Iperf or thrulay to test TCP or UDP throughput
„ dast.nlanr.net/Projects/Iperf/
„ www.internet2.edu/~shalunov/thrulay/
‹NDT
„ What are the interface speeds?
„ What is the bottleneck?
„ Is there a duplex mismatch?
„ Are buffers set right (both ends)?
Les Cottrell, SLAC
Slide: 25
NDT example (Rich Carlson)
Les Cottrell, SLAC
Slide: 26
“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 address
47cottrell@netflow:~>nslookup
Server: localhost
Address: 127.0.0.1
Name:
lhr.comsats.net.pk
Address: 210.56.16.10
210.56.16.10
‹ Use a whois server, e.g.
z www.networksolutions.com/cgi-bin/whois/whois (Americas & Africa)
z www.ripe.net/cgi-bin/whois (Europe)
z www.apnic.net/ (Asia)
z May identify site name, address, contact, etc, not all domains are in
databases (e.g. will not find comsats.net.pk)
Les Cottrell, SLAC
Slide: 27
“Where is” a host – cont.
‹ Find the Autonomous System (AS) administering
„ Form giving AS for domain name
zhttp://www.fixedorbit.com/search.htm
zGives AS number, name adjacent AS’s web page for
AS
„ Given an AS find out more about it:
zUse 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
zwww.telstra.net/ops/bgp/bgp-as-upsstm.txt
zTells what AS is upstream of an ISP
Les Cottrell, SLAC
Slide: 28
“Where is” a host - cont.
‹May be able to get latitude & longitude:
„ http://www.hostip.info/index.html
„ http://www.ip2location.com/
zBut it is a subscriber service ($$$, but …), however it is
probably best for developing regions
‹Triangulate pings from landmarks (in development)
„ planetlab-01.ipv6.lip6.fr:10000/cbg.php
Les Cottrell, SLAC
Slide: 29
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
Les Cottrell, SLAC
Slide: 30
What ya gonna tell ‘em?
‹ Describe problem with details
„ What is affected?
z Application, host OS (uname –a), NIC (ifconfig, route)
„ How is it affected?
z Non responsiveness, unable to contact remote host
z 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)…
Les Cottrell, SLAC
Slide: 31
Web page examples: Case studies
‹http://www.slac.stanford.edu/grp/scs/net/case/html/
‹http://e2epi.internet2.edu/case-studies/
Les Cottrell, SLAC
Slide: 32
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
‹IEPM/PingER home site
„ www-iepm.slac.stanford.edu/
„ IEEE Communications, May 2000, Vol 38, No 5, pp 130-136
Les Cottrell, SLAC
Slide: 33