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  • IPv4

    Lab 1.4 – IPv4 Packet Analysis

    This lab focused on examining network traffic at the IPv4 layer, with an emphasis on identifying abnormal or suspicious behavior within the packet capture.

    Lab Setup

    For this exercise, I used the capture file called ipv4.pcap.

    Once downloaded, I opened the file in Wireshark and began my analysis.

    Exercise 1 – Analyzing the First IPv4 Packet

    a) What version of IP is the first packet?

    We can find this either by looking at the Ethernet header or the IP header. Looking at the IP Header, the IP version is located in the higher-order nibble of the 0 byte offset. We can see there that this is an IPv4 packet.

    b) What is the IP Time To Live value, in decimal, in this packet?

    To answer this, I examined the IPv4 header of the first packet in the ipv4.pcap file. I specifically looked at the Time To Live (TTL) field, which determines how many hops (routers) the packet can pass through before being discarded.

    The TTL field is located 8 bytes into the IP header, but Wireshark conveniently displays this value directly in the decoded packet details. In this case, the TTL value was 64, which is a common default for Linux-based systems.

    This value can also give clues about the operating system or network behavior based on how far the packet has traveled.

    c) What is the source IP address, in hexadecimal, in the first packet?

    To find the source IP address in hexadecimal, I examined the IPv4 header in the first packet of the ipv4.pcap capture. The source IP address is located between bytes 12 and 15 from the start of the IP header.

    Wireshark makes this easy by displaying both the decimal and hexadecimal representations. For the first packet, the source IP is 192.168.11.65 in decimal, which corresponds to 0xc0 0xa8 0x0b 0x41 in hexadecimal.

    d) What is the destination IP address, in hexadecimal, in the first packet?

    To find the destination IP address in hexadecimal, I examined the IPv4 header of the first packet in the ipv4.pcap file. According to the IP header structure, the destination IP is stored between bytes 16 and 19 from the start of the IP header.

    Wireshark clearly shows this value in both hexadecimal and decimal. In this case, the destination IP is 192.168.1.1, which corresponds to the hexadecimal representation 0xc0 0xa8 0x01 0x01.

    Exercise 2 – Identifying Abnormalities in the IPv4 Header

    In this exercise, I examined the second packet in the ipv4.pcap capture and identified two key problems with its IP header.

    Problem 1: Invalid IP Version
    The first issue is that the IP header lists version 8, which is not a valid or supported IP version. Only versions 4 and 6 are in use today. Because of this, Wireshark marks the packet in red and does not attempt to decode it further.

    Problem 2: Invalid Header Checksum
    After inspecting the raw packet bytes, I found another issue in bytes 10 and 11, which represent the IP header checksum. The value was 0x0000, which is invalid and indicates the packet may have been corrupted or crafted improperly.

    Impact
    Both of these abnormalities would cause the packet to be dropped immediately by the first router or system it attempts to pass through. This exercise helped me understand how malformed packets are detected and discarded at the network layer.

    Exercise 3 – Hex Analysis Using tcpdump

    In this part of the lab, I used the tcpdump command-line tool to inspect raw packet data and answer questions related to the third packet in the ipv4.pcap capture.

    To extract the first few packets in hexadecimal format, I ran:

    a) What version of IP is this packet? What is the header length if the packet ?

    By looking at the raw hexadecimal output of the third packet, I found it starts with the byte 0x45. This first byte breaks down into two nibbles:

    • 4 → IP version
    • 5 → header length

    So, the version number of this packet is IPv4, as indicated by the high-order nibble of the first byte.

    The header length field is in units of double word so it has to be multiplied by 4 to be converted to a length of 20 bytes.

    b) What is the embedded protocol in this packet, according to the IP header?

    To determine the embedded protocol, I examined byte offset 9 in the IP header of the third packet. This byte indicates which protocol is encapsulated within the IPv4 packet.

    Using the tcpdump output, I located the value at this offset. For this packet, the value was 0x01, which corresponds to ICMP (Internet Control Message Protocol).

    Exercise 4 – Calculating ICMP Header and Data Length

    In this task, I analyzed the fourth packet in the ipv4.pcap file to determine how many bytes were used by the ICMP header and data, following the IPv4 header.

    To do this, I used two values from the IP header:

    • Total Length: 68 bytes (it is found in the 3rd byte offset of the IP Header // it has a hexadecimal value of 0x44)
    • Header Length: 20 bytes (which is shown as a value of 5 in the header, multiplied by 4)

    By subtracting the IP header length from the total IP datagram size:
    68 - 20 = 48 bytes

    So, the ICMP header and data together occupy 48 bytes in this packet.

  • The Network Access/Link Layer

    Link Layer Analysis Lab – Overview and Setup

    This set of exercises focuses on analyzing network activity at the Link Layer.

    Lab Setup

    For this lab, I used Wireshark to analyze a file called link.pcap.

    Exercise 1 – Analyzing the First Record

    1. In the first record, what is 192.168.11.11 trying to find?

    To answer this, I examined the first packet in the link.pcap file.

    We can see that this an ARP request going from mac address aa:00:04:00:0a:04 (which is the mac address associated with the IP address 192.168.11.11) to the mac address ff:ff:ff:ff:ff:ff (the broadcast address). It is looking for the mac address associated with the IP address 192.168.11.1

    2. What is the Ethernet destination address in the ARP request? Why is the request sent to this address?

    While examining the ARP request in the packet capture, I checked the Ethernet II header to find the destination MAC address. In an ARP request, this address is typically set to the broadcast address ff:ff:ff:ff:ff:ff.

    This is done because the sender doesn’t yet know the MAC address of the target IP and needs to ask all devices on the local network if they are the owner of that IP address. Broadcasting ensures that the request reaches every host on the subnet.

    3. What is the hexadecimal Ethernet II Type for an ARP request?

    It is 0x0806

    4. What is the Target MAC address of the ARP request? Why do you suppose this address is used?

    When analyzing the ARP request in Wireshark, I checked the Target MAC address field in the ARP header. This field was set to 00:00:00:00:00:00.

    This makes sense because the sender is trying to discover the MAC address of the target IP—they don’t know it yet. The all-zero MAC address is used as a placeholder to indicate that this information is currently unknown and is the whole reason the ARP request is being broadcast.

    5. Examine record 2. What type of ARP is this?

    In record 2 of the capture, I analyzed the ARP packet details in Wireshark. Based on the fields, I could tell this was an ARP reply. Unlike an ARP request, which is broadcast to ask for a MAC address, the ARP reply is a direct response from the device that owns the IP address, providing its MAC address to the requester.

    This completes the ARP resolution process, allowing the devices to communicate at the Ethernet level.

    6. What is the Sender MAC address of 192.168.11.1?

    To answer this, I looked at the ARP reply packet in the capture where 192.168.11.1 is listed as the sender. In the ARP header, the Sender MAC address field contains the hardware address associated with that IP (00:0c:29:03:23:19). This is the MAC address the device is announcing to the network, and it’s what other hosts will use to communicate at the Ethernet layer.

    7. What is the MAC address of the intended recipient of this ARP message?

    To determine the intended recipient’s MAC address, I examined the Target MAC address field in the ARP reply. This field shows the hardware address (aa:00:04:00:0a:04) of the device that originally sent the ARP request.

    Exercise 2 – Interpreting Linked ARP Activity

    Examine records 3, 4, and 5, which are all associated with each other. What do you think is happening?

    After examining records 3, 4, and 5, it became clear that something suspicious was occurring with the ARP replies.

    In record 3, host 192.168.11.4 sends an ARP request asking for the MAC address of 192.168.11.111.
    In record 4, a legitimate response comes from 192.168.11.111, returning its correct MAC address.
    However, in record 5, a second ARP reply is sent—also claiming to be from 192.168.11.111, but with a different MAC address.

    This is a red flag. The presence of two conflicting ARP replies suggests that someone is attempting to poison the ARP cache of the original requester (192.168.11.4). The attacker is trying to trick it into associating the IP address 192.168.11.111 with the attacker’s MAC address, effectively redirecting traffic meant for the legitimate host.

    This is a classic example of ARP spoofing, a technique used in man-in-the-middle (MITM) attacks to intercept or manipulate traffic. The warning in Wireshark also highlights this as a duplicate IP address issue, which further confirms the attempt to mislead the network.

    Exercise 3 – Analyzing Suspicious MAC-to-IP Associations

    In this exercise, I reviewed packets 6 through 55, which represent a small sample of many similar records captured during an attack simulation using the macof tool. The focus was on analyzing the Ethernet headers at the link layer.

    1. What is the source MAC address of records 6, 7, and 8?
    I checked each record and found that all three packets had different source MAC addresses:

    • Record 6: 67:aa:17:2f:ba:02
    • Record 7: ac:1d:9d:2e:7c:71
    • Record 8: c6:58:a2:5e:02:49

    2. What is the source IP address in records 6–55?
    All of these packets used the same source IP address: 10.10.10.5.

    3. What is wrong with these MAC address-to-IP address associations? What does this indicate?
    This behavior is highly abnormal. Multiple packets are using different MAC addresses while claiming the same IP address. This inconsistency suggests that the traffic is spoofed, which is a hallmark of a MAC flooding attack. Tools like macof generate thousands of fake MAC/IP combinations to overflow the switch’s MAC address table, potentially forcing it into fail-open mode, where it floods traffic to all ports—opening the door to packet sniffing by an attacker.

  • Introduction to Wireshark

    The goal of this lab is to familiarize myself with the basic functionalities of Wireshark.

    Exercise 1 – Wireshark Profile Setup

    To kick off the lab, I started by setting up a custom Wireshark configuration profile. These profiles are really helpful because they let you tailor things like display columns, settings, and layout to match your workflow. You can switch between different profiles depending on what you’re analyzing, and it’s easy to import/export them to share with others.

    For this exercise, I used a pre-made profile provided for the class. I opened Wireshark on my system and imported the SEC503.Wireshark.profile.zip file. Once that was in place, I loaded the wireshark.pcap capture file, which set me up to move on to the next part of the lab (Exercise 2).

    Exercise 2 – Identifying TCP Protocols in the PCAP

    In this part of the lab, I analyzed the provided wireshark.pcap file to identify the different TCP-based protocols present in the capture.

    By going to the Statistics menu in Wireshark and selecting Protocol Hierarchy, I was able to quickly identify the three TCP protocols used in the capture file. This feature provides a clear breakdown of all protocols seen in the traffic, making it easy to spot which ones are running over TCP:

    -SSH

    -MySQL

    -Internet Relay Chat

    How many different IP addresses were involved in conversations in this pcap?

    To answer this, I opened the Conversations window under the Statistics menu in Wireshark. This tool displays all IP-level conversations and allowed me to easily identify how many unique IP addresses were communicating in the capture. It’s a quick way to get an overview of the network activity and see which hosts were involved.

    We can see that 4 different IP addresses were involved in 3 conversations in this file.

    What is the largest number of Bytes exchanged in any IPv4 conversation?

    To determine the largest number of bytes exchanged in any IPv4 conversation, I used the IPv4 Conversations tab under Statistics > Conversations in Wireshark. This view lists the total byte count for each conversation.

    From the output, I found that the highest byte exchange between any two hosts was 31k. This gave me a quick insight into which conversation involved the most data transfer within the capture.

    Exercise 3 – Counting TCP Conversations

    How many different TCP conversations are in this pcap?

    For this exercise, I used the Statistics > Conversations feature in Wireshark and navigated to the TCP tab. This tab lists all the unique TCP sessions found in the capture file. Each entry represents a separate conversation between two IP addresses over TCP.

    We can see 4 different TCP conversations in this file.

    What is the duration of the conversation that lasted the longest?

    To answer this, I stayed in the TCP tab under Statistics > Conversations in Wireshark. This view includes a Duration column, which shows how long each TCP conversation lasted. By scanning this column, I identified the conversation with the longest duration (776.1629 seconds)

    Exercise 4 – Inspecting Ethernet Type

    Before starting this task, I made sure that all three Wireshark panes were visible: the packet list, packet details, and packet bytes. If they weren’t showing, I adjusted the window size by dragging from the bottom-right corner until they appeared.

    Navigate to the first packet in the pcap. What is the hexadecimal value of the Ethernet type?

    I selected the first packet in the capture and expanded the Ethernet II section in the middle pane. From there, I located the Type field, which shows the Ethernet type in hexadecimal format (0x0800). This value indicates the protocol being used at the next layer (IPv4 here).

    What is the IP Time To Live Value?

    We can find it by expanding the IPv4 section in the middle pane and find that the value is equal to 64.

    What transport layer follows the IP layer?

    We can find our answer right under the TTL line under Protocol. Hre we can see that the transport layer is TCP (which corresponds to an Hexadecimal value is 0x06)

    What is the last hexadecimal byte value of the TCP header ?

    By clicking on the TCP header in the middle pane, the entire TCP header gets highlighted in the lower pane and we can see that the last hexadecimal byte value is 0xef

    Exercise 5 – Inspecting MySQL Traffic

    As identified earlier using Protocol Hierarchy Statistics, the pcap file contains MySQL traffic. According to the instructions, there is a single MySQL session that begins at packet 372.

    Locate the MySQL session that begins in packet 372. Follow the MySQL TCP conversation. What is the version of the MySQL server package for Ubuntu?

    To complete this task, I navigated to packet 372 by going to the Go menu and selecting the Go To Packet option:

    I then right-clicked on it to select Follow > TCP Stream. This allowed me to view the entire MySQL session in context. By examining the initial handshake and server response, I was able to extract the MySQL version number used in the Ubuntu server package (5.0.51a-3ubuntu5.8). This kind of inspection is useful for identifying software versions and potential vulnerabilities in network traffic.

    What is the name of the SQL Table that the user performs an Insert Into command on?

    At the bottom of the TCP stream, we can see that the command is performed on a table called “auth_users”.

    Exercise 6 – Finding a Specific String in Packet Data

    What is the last packet that contains the string “beer”?

    To complete this exercise, I used Wireshark’s Find Packet feature by pressing Ctrl + F and switching the search type to String within Packet Bytes. I then searched for the keyword “beer”.

    Wireshark highlighted each packet containing this string. I scrolled through the results to locate the last packet in the capture that contained “beer” and recorded its packet number (470). This was a fun way to practice content-based searches within packet data.

  • Concepts of TCP/IP

    Objective:
    In this lab, I explored various aspects of the TCP/IP protocol by using tcpdump to analyze network traffic. The goal was to familiarize myself with the functionality of tcpdump and practice using its command-line options to read and interpret packet capture files.

    Exercise 1: Reading a PCAP File
    The first exercise involved using tcpdump to read a packet capture file named concepts.pcap. The objective was to analyse the contents and identify the number of recorded packets. I utilized the following command to read the file:

    Six records are displayed:

    Exercise 2: Reading Specific Records from a PCAP File

    Objective:
    In this exercise, I practiced using tcpdump to read a specified number of records from a packet capture file. The goal was to extract and display the first two records from the file concepts.pcap efficiently as well as identify the source IP address of the second record .

    Command Explanation:
    To achieve this, I used the following tcpdump command:

    • The -c 2 option instructs tcpdump to limit the output to the first two records.
    • The -t option suppresses the display of timestamps, making the output more concise.
    • The -n option ensures that IP addresses are displayed as numerical values rather than being resolved to hostnames.
    • The -r option specifies that tcpdump should read from the file rather than capturing live traffic.

    These options can be combined in a single command for efficiency.

    The second source IP address is 192.168.11.13 which is found here:

    Exercise 3: Displaying Network Records in Hexadecimal

    Objective:
    In this exercise, I learned how to use tcpdump to read a single record from a packet capture file and display it in hexadecimal format. This technique is useful when analyzing raw packet data for low-level protocol analysis. I am also asked to identify the first two bytes seen on the hex dump for the first record, the IP protocol field value and the TTL located the IP header.

    Command Explanation:
    To view the first record from the file concepts.pcap in hexadecimal format, I used the following command:

    The -x option displays the packet data in hexadecimal format.

    Regarding the first two bytes question: A hexadecimal character represents 4 bits (or a nibble), so a byte corresponds to 2 hexadecimal characters. The first two bytes are 0x45 and 0x00, respectively.

    The IP protocol field value is 0x01. It is a one-byte field located in the 9th byte offset from the beginning of the IP header. This tells us that the embedded transport protocol is ICMP.

    The TTL is located in the 8th byte offset from the beginning of the IP header and like the IP protocol field is a one-byte field. it is equal to 0x40 or 16*4 + 1*0 = 64 in decimal value.

    Exercise 4: Displaying MAC/Ethernet Addresses from a PCAP File

    Objective:
    In this exercise, I practiced using tcpdump to display the MAC (Media Access Control) addresses from a packet capture file. The goal was to read the first record from the file concepts.pcap and identify both the source and destination MAC addresses.

    Command Explanation:
    To display the MAC addresses from the first record, I used the following command:

    The -e option displays the link-layer (MAC/Ethernet) headers, showing both source (00:04:00:0a:04) and destination (00:0c:29:03:23:19) MAC addresses.

    The -v option increases the verbosity of the output, providing more detailed information about each packet. I can easily identify the ethertype which indicates which protocol follows the ethernet header (in this case it is IPv4). I can also quickly see that the protocol following the IP header is ICMP (It can be seen in the “proto” field).

    Exercise 5: Analyzing DNS Traffic in UDP Packets

    Objective:
    In this exercise, I analyzed DNS traffic captured in a PCAP file using tcpdump. The goal was to identify the type of activity and data within specific UDP packets, focusing on DNS queries and responses.

    Using the same command as in the last exercise, we can see the following two packets:

    The output displayed two consecutive UDP packets related to DNS activity:

    1. Source and Destination:
      • Source IP: 192.168.11.65, Source Port: 52894
      • Destination IP: 192.168.11.53, Destination Port: 53 (DNS port)
    2. Packet Details:
      • The first packet contains a DNS query (A? giac.org.), indicating that the client is requesting the IP address for the domain giac.org.
      • The second packet contains the DNS response, indicating that the server resolved giac.org to the IP address 66.35.45.203.
      • Both packets use the UDP protocol (proto UDP (17)).
      • The length of the first packet is 54 bytes, while the response packet is 70 bytes.

    Analysis:
    The presence of port 53 in the packet indicates DNS traffic. The query type (A?) specifies that the client is requesting an IPv4 address for the domain giac.org. The response from the DNS server includes the resolved IP address, confirming that the communication was successful.