Network Problem diagnosis for non

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SPACE Weather School:

Basic theory & hands-on experience

Network Problem

Diagnosis for Nonnetworkers

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 http://www.slac.stanford.edu/grp/scs/net/talk10/diagnosis.pptx

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

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 Findings may be out of date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

 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

Les Cottrell, SLAC Slide: 4

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

Les Cottrell, SLAC Slide: 5

First steps

 Command prompt, find out about network connection

 ipconfig ?

 ipconfig

 Default gives IP address, gateway/1 st 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 ?

Les Cottrell, SLAC Slide: 6

Ping on Windows

IP address of target RTT target

Specify number pings

C:\Users\cottrell> ping –n 4 –l 32 mail.alex.edu.ca

Size of packet

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

Try: ping –t, what use is ping -f

?

Les Cottrell, SLAC Slide: 7

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

Anomalies

Pings blocked

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

Les Cottrell, SLAC Slide: 8

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

Les Cottrell, SLAC Slide: 9

 Try:

1.

ping localhost

2.

ping mail.alex.edu.eg

3.

ping sohag-univ.edu.eg

4.

ping www.minia.edu.eg

5.

ping www.alex.edu.eg

Les Cottrell, SLAC Slide: 10

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/wanmon/viper/tulip_map.htm

Les Cottrell, SLAC Slide: 11

RTT from California to world

Europe

300ms

RTT (ms.)

Les Cottrell, SLAC

300ms

0.3*0.6c

Longitude (degrees)

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

200

100

0

Les Cottrell, SLAC

Terrestrial

Country

Slide: 13

Traceroute Rough algorithm

Rough traceroute algorithm ttl=1; #To 1 st 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++

}

Les Cottrell, SLAC Slide: 14

Traceroute (tracert on Windows)

C:\Users\cottrell> tracert

Max hops Target IP address gets help

3 RTTs

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 1 ms 1 ms 1 ms 10.13.11.1

2 1 ms <1 ms 1 ms 10.100.100.53

Router IP address

3 1 ms <1 ms <1 ms 10.0.0.3

4 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

No response

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 tracert www.lbl.gov

Why do the first hops take so long to reply?

Try tracert –d www.lbl.gov

Les Cottrell, SLAC Slide: 15

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)

Les Cottrell, SLAC Slide: 16

Traceroute from elsewhere

 Traceroute to remote host

 Is the route direct, over commercial congested nets

 Reverse traceroute from remote host to you or 3 rd party

 www.slac.stanford.edu/comp/net/wan-mon/traceroute-srv.html

 www.tracert.com/

 visualroute.visualware.com/ # requires Java

Visualroute servers in Europe

Les Cottrell, SLAC Slide: 17

Traceroute server results

 Example: www.slac.stanford.edu/cgi-bin/nph-traceroute.pl

Related info

Security warning

Traceroute

Your IP name

Les Cottrell, SLAC

Your IP address Enter IP address or name

Slide: 18

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

 traceroute www.slac.stanford.edu

140

Les Cottrell, SLAC Slide: 19

Pingroute example

 May help tell where losses start

 Will need many pings if losses small

Start of losses?

Les Cottrell, SLAC

But?

Start of sustained losses

Routers may not respond

Slide: 20

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

Les Cottrell, SLAC Slide: 21

Pathping en.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% |

Default probes/hop = 100

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]

|=Link

Router

No RTT variance provided

Help try pathping

Trace complete.

Les Cottrell, SLAC Slide: 22

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

Les Cottrell, SLAC Slide: 23

 Look for change in measured value

 Note time

 Correlate

Example time series

Italy disconnected

Les Cottrell, SLAC Slide: 24

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)?

Les Cottrell, SLAC Slide: 25

NDT example

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

Les Cottrell, SLAC Slide: 26

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

Les Cottrell, SLAC Slide: 27

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

)

Les Cottrell, SLAC Slide: 28

“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 whois server (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)

Les Cottrell, SLAC Slide: 29

“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

Les Cottrell, SLAC Slide: 30

“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

Les Cottrell, SLAC Slide: 31

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: 32

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)…

Les Cottrell, SLAC Slide: 33

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/

Les Cottrell, SLAC Slide: 34

More slides

Les Cottrell, SLAC Slide: 35

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

Les Cottrell, SLAC Slide: 36

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

Missing seq #

Summary

--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: 37

Traceroute

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

Remote host host

Probes/hop

Max hops (20)

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 location

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

Long delay satellite

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

No response:

12 islamabad-gw2.comsats.net.pk (210.56.8.4) 751.851 ms

13 *

Lost packet or router

14 lhr.comsats.net.pk (210.56.16.10) 827.301 ms ignores

Les Cottrell, SLAC Slide: 38

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 avaialable

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: 39

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/SLACnetflow.html

 SNMP based tools

Les Cottrell, SLAC Slide: 40

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