IP Network Troubleshooting Part 3. Wayne M. Pecena, CPBE, CBNE Texas A&M University Educational Broadcast Services - KAMU

Transcription

1 IP Network Troubleshooting Part 3 Wayne M. Pecena, CPBE, CBNE Texas A&M University Educational Broadcast Services - KAMU February 2016

2 Today s Outline: Focused Upon Protocol Analysis with Wireshark Review of Wireshark Basics & How to Capture Network Traffic Creating Custom Wireshark Views Creating Custom Pre & Post Wireshark Filters Detailed Capture Analysis Examples Alternatives to Wireshark & Why Might These Might Be Considered Additional Useful Tools Takeaways, Questions, and Maybe Some Answers 2

3 Review of Wireshark Basics & How to Capture Network Traffic 3

4 Obtain & Install Wireshark Available for Windows, Mac OSx, & Linux Download (current v2.0.1): Be Sure to Include Libraries: WinPcap (Windows) Libpcap (Unix/Linux) Install Start Wireshark Select Interface Click Start CTRL+E will Stop You Have Created a PCAP File! View & Analyze Results Save For Later Analysis

5 Wireshark Host Requirements Windows 10, 8, 7, Vista, Server 2016, Server 2012, Server 2008 R2, and Server 2008 Apple OSx, Debian GNU/Linux, FreeBSD, Mandriva Linux, NetBSD, Red Hat Enterprise/Fedora Linux, and several others.. 64-bit AMD64/x86-64 or 32-bit x86 processor. 400 MB available RAM. Larger capture files require more RAM. 300 MB available disk space. Capture files require additional disk space ( or higher recommended) resolution / 16 bit color minimum. A supported Network Interface Keep in Mind: Don t Use Your Old Retired PC As an Wireshark Capture Host Capturing on a 100 Mbps network can produce hundreds of megabytes of capture data in a very short time. A fast processor, lots of memory and disk space is always a good idea. 5

6 Captured Packet(s) Selected Header Data Decoded Payload Data Decoded Hexadecimal & ASCII

7 Application Presentation Session Transport Layer 3 Device Application Presentation Session Transport Network Layer 2 Device Network Network Layer 2 Device Network Data Link Data Link Data Link Data Link Data Link Data Link Data Link Data Link Physical Physical Physical Physical Physical Physical Physical Physical 7

8 Encapsulation OSI Model Data Flow Layers Transport Network Data Link Physical Protocol Data Unit Segments Packets Frames Bits 8

9 Where to Tap? Problem Nature Often Determines: At Problem Host At Destination Host Mid-Network Locations Accessibility May Also Drive Tap Point Remember: Interfaces are Bi-Directional

10 How to Tap Ethernet & Capture Packets Can Be Challenging! How to Capture? UTP Ethernet: Physical Passive Tap Active Tap Optical Ethernet: Physical Passive Tap Active Tap Ethernet Switch Port Mirror Run Wireshark on Client Host if Possible

11 Active Tap Devices UTP Taps Optical Taps

12 Shared Media Approach 100 Mbps Maximum Half-Duplex Only Host Device A Ethernet Hub Host Device B Commonplace In Wireless Environment Wireshark Capture Host It Was Simpler In The Past Half-Duplex Shared Media Networks Not Commonplace Today 12

13 Switched Media Approach Host Device A Ethernet Switch Host Device B Normal Ethernet Switch Operation Prevents Network Traffic Between Host A and Host B To-Be-Seen by the Wireshark Capture Host Wireshark Capture Host 13

14 Switched Media Hub Approach Host Device A Ethernet Switch Ethernet Hub Host Device B Works, But Downgrading Network To Half-Duplex Ethernet Switch Now Sees 2-MAC Addresses (problem if switch-port security is enabled) Wireshark Capture Host 14

15 Switched Media Tap Approach Host Device A Ethernet Switch Ethernet Tap Host Device B?? Works, But Often Costly Especially When GigE UTP Or Optical Network Involved Wireshark Capture Host 15

16 Switched Media Monitor Port Approach Host Device A Ethernet Switch Monitor Port Enabled Host Device B Monitor Port Recommended Approach (where possible) Wireshark Capture Host 16

17 Keep In Mind! Host Device A Ethernet Switch Monitor Port Enabled Host Device B 500 Mbps Network Traffic 500 Mbps Network Traffic Monitor Port 1000 Mbps Network Traffic Limitations: Bad Frames Not Mirrored No VLAN Tags Passed Caution With RTP Network Traffic Wireshark Capture Host Remember: Tapping a Network Can Be Challenging! 17

18 Cisco Ethernet Switch SPAN Port Host A Host B Port 1 Port 23 config t Switched Port Analyzer (SPAN) Port Port 14 monitor session 1 source interface fa0/1 monitor session 1 source interface fa0/23 monitor session 1 destination interface fa0/14 exit Wireshark Host

19 HP Procurve Ethernet Switch Port Mirror Host A Host B Port 1 Port 23 HP Procurve 2915 Port 14 Mirror or Monitor Port config mirror-port 14 int 1, monitor (int 1-12, monitor) int 23, monitor Wireshark Host show monitor exit

20 Creating Custom Wireshark Views 20

21 frame 192 selected Header Details Displayed Payload Data Decoded (hex & ASCII)

22 View Screen Layouts 22

23 Default View Colors 23

24 Customize Columns 24

25 Creating Custom Pre & Post Wireshark Filters 25

26 Filtering Capture Filters Selectively Capture Packets Pre-Capture Configuration Minimizes Amount of Captured Data Display Filters Applied When Viewing Allows Focusing on Attribute(s) All Data is Retained Which One to Use? Reason for Capturing Dictates Proper Filter Use Use Capture Filter When You Know What You Are Looking For Remember: You Can t Display What Has Not Been Captured!

27 Using Capture Filters 27

28 Useful Capture (pcap) Filter Examples ip tcp udp host host /26 host mask src net /26 dst net /26 port 80 not broadcast and not multicast 28

29 Using Display Filters 29

30 Useful Display Filter Examples eth.addr==00:19:c8:c8:22:7f ip ip.addr== ip.addr== or ip.addr== tcp tcp.port==80 udp udp.port==50000 http 30

31 Detailed Capture Analysis Examples 31

32 TCP 3-Way Handshake SYN ACK SYN, ACK Find the 1 st SYN Packet: Edit>Find Packet Enter tcp.flags.syn==1 Right Click on Packet Select Follow TCP Stream 32

33 ICMP Example 33

34 Streaming Media Example 34

35 Wireshark Statistics 35

36 Alternatives to Wireshark & Why Might These Might Be Considered 36

37 Fluke Networks Clearsight 37

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39 Additional Useful Tools 39

40 zenmap nmap security scanner GUI 40

41 Wireless Networks & Wireshark Wireless is challenging! Most Network Adapters Do Not Support Promiscuous Mode If Promiscuous Mode is Available You Only See Packets To-From the Host Running Wireshark! You Must Select RF Channel (Wireshark capture options) You Will Only See Packets on That RF Channel Extensively Use Capture Filters! Focus Upon a Specific Client 41

42 Takeaways, Questions, and Maybe Some Answers 42

43 Takeaway Points & Concepts: Parts 1-3 Establish a Structured Troubleshooting Approach Avoid Shooting from the Hip Approach(s) Use the OSI Model as a Guide to a Structured Approach Work You Way Up the IP Stack Verify Layer 1 Physical Connectivity Verify Layer 2 Connectivity is Error Free Verify Layer 3 Inter-Networking Use Protocol Analysis to See Network activity 80% of Network Problems is Physical Infrastructure Based Standards Not Properly Applied Guidelines Not Adhered To Don t Loose Sight of 100m Ethernet UTP Segment Limit! 43

44 Takeaway Points & Concepts. Use Protocol Analysis to See Network Host Interaction Wireshark Is The Most Popular Protocol Analyzer Understanding the OSI Model & TCP/IP Protocol Action is Key to Understanding Wireshark Results Understand How & Where to Capture Network Activity Filtering is Essential to Find the Needle in the Haystack Capture Filters (minimize captured data) Display Filters (minimize displayed info) Customize Your Wireshark Views Verify Everything Yourself Caution Trusting What You Are Told! 44

45 References Further Study

46 Utilize a Structured Process to Troubleshooting! 46

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48 Thank You for Attending! Wayne M. Pecena Texas A&M University ? Questions? 48