Verify Current System State

• Check the current NX-OS version:

show version

Verify the system is stable and there are no issues:

show module
show system resources

1. Download the NX-OS Image
   • Obtain the correct NX-OS image from Cisco’s official website.
   • Ensure the image is compatible with your Nexus 3000 model and the features you need.
2. Copy the NX-OS Image to the Device
   • Copy the image to the switch using TFTP, FTP, SFTP, or SCP:

copy scp://[username]@[server]/[path_to_image]/[image_name].bin bootflash:

• Replace [username], [server], [path_to_image], and [image_name] with your actual server and image details.

show file bootflash:[image_name].bin md5sum

• Confirm the checksum matches the one provided by Cisco.

install all nxos bootflash:[image_name].bin

Alternatively, if your device doesn’t support ISSU (In-Service Software Upgrade), you’ll need to perform a disruptive upgrade:

boot nxos bootflash:[image_name].bin

Reload the System

• If required (for a disruptive upgrade), reload the switch to boot into the new image:

reload

• Confirm the reload if prompted.

show version

Post-Upgrade Checks

• Ensure all services and protocols are running as expected:

show feature
show interface brief

Check the logs for any errors:

show logging

Save the Configuration

• Save the running configuration to the startup configuration:

copy running-config startup-config

Backup Configuration

• It’s good practice to backup your configuration after an upgrade:

copy running-config scp://[username]@[server]/[destination_path]/[config_backup].cfg

How to Collect PCAP Files

Using Wireshark:

1. Download and Install Wireshark: First, download Wireshark from the official website and install it on your system.
2. Start a Capture: Open Wireshark and select the network interface you want to capture traffic from. Click the shark fin icon to start capturing packets.
3. Apply Filters (Optional): You can apply filters to narrow down the traffic you’re interested in. For instance, use ip.addr == 192.168.1.1 to filter traffic to and from IP address 192.168.1.1.
4. Stop the Capture: Click the red square icon to stop capturing once you’ve collected enough data.
5. Save the Capture: Go to File > Save As and save your capture file (.pcap or .pcapng format) for analysis.

Using tcpdump on Linux:

1. Install tcpdump (if necessary): On most Linux distributions, you can install tcpdump using the package manager, e.g., sudo apt install tcpdump on Debian/Ubuntu.
2. Capture Packets: Use a command like sudo tcpdump -i eth0 -w capture.pcap to capture packets on the eth0 interface and write them to capture.pcap. Replace eth0 with the appropriate interface name for your system.
3. Stop the Capture: Press Ctrl+C to stop capturing.

What to Check in PCAP Files

Example 1: Connectivity Issues

• Symptom: A user cannot connect to a web server.
• Analysis: Look for TCP three-way handshake (SYN, SYN-ACK, ACK) sequences. If you see SYN packets without corresponding SYN-ACK responses, the connection attempt is likely being blocked or the destination is unreachable.

Example 2: High Latency

• Symptom: Applications are experiencing slow response times.
• Analysis: Check the timestamps between packets in a TCP stream (filter: tcp.stream eq 1). Long delays between SYN and SYN-ACK or between data packets and their acknowledgments indicate high latency.

Example 3: DNS Issues

• Symptom: Domain names do not resolve.
• Analysis: Filter DNS traffic using dns. Look for DNS queries (A or AAAA records) without responses or with failure response codes (e.g., NXDOMAIN).

Example 4: Packet Loss

• Symptom: Unstable network connections and performance.
• Analysis: Check for TCP retransmissions (filter: tcp.analysis.retransmission). Frequent retransmissions suggest packet loss.

Example 5: Misconfigured Firewall or Security Devices

• Symptom: Legitimate traffic is dropped or blocked.
• Analysis: Look for TCP resets (RST packets) immediately following a successful handshake or during an established connection. Unexpected RST packets often indicate that a firewall or security device is interrupting the flow.

Example 6: Broadcast Storm

• Symptom: Network slowdown or collapse.
• Analysis: Filter for broadcast traffic (eth.dst == ff:ff:ff:ff:ff:ff). A high volume of broadcast packets can overwhelm network resources.

Example 7: ARP Poisoning

• Symptom: Man-in-the-middle (MITM) attacks or IP conflicts.
• Analysis: Filter ARP traffic (arp). Look for multiple ARP responses (ARP is at) from different MAC addresses claiming the same IP address, indicating a potential ARP poisoning attack.

Frequent TCP Retransmissions: Indicates network congestion or packet loss.

===================================

Interpreting Error Logs

Error logs in PCAP files aren’t explicitly labeled as such, but certain patterns can indicate problems:

Continuous ARP Requests without Replies: Indicates the queried device is unreachable at Layer 2.

No. Time Source Destination Protocol Length Info
162 2.312345 192.168.1.100 Broadcast ARP 60 Who has 192.168.1.1? Tell 192.168.1.100

DNS Queries without Responses: Suggests DNS issues or misconfigurations.

No. Time Source Destination Protocol Length Info
204 3.123456 192.168.1.100 8.8.8.8 DNS 74 Standard query 0x2aaf A example.com

Frequent TCP Retransmissions: Indicates network congestion or packet loss.

No. Time Source Destination Protocol Length Info
438 5.678901 192.168.1.100 93.184.216.34 TCP 66 [TCP Retransmission] 443 > 51762 [ACK] Seq=1 Ack=1 Win=65535 Len=0

=====================================

When analyzing a PCAP file for network connectivity issues, you’re essentially looking for clues that indicate where the communication breakdown is occurring. Below are 10 examples of what to look for in PCAP files to diagnose network issues.

Example 1: DNS Lookup Failures

Symptom: Unable to resolve domain names.

What to Look For: Filter DNS traffic using dns filter. Check for DNS queries without corresponding DNS responses, or responses with error codes, indicating a DNS resolution issue.

Example 2: ARP Issues

Symptom: Local network connectivity problems.

What to Look For: Filter ARP traffic with arp and look for unanswered ARP requests. Repeated ARP requests for the same IP without a reply suggest the destination host is unreachable at the data link layer.

Example 3: TCP Retransmissions

Symptom: Slow network responses and timeouts.

What to Look For: Use tcp.analysis.retransmission filter to identify retransmitted packets. Frequent retransmissions indicate packet loss or network congestion.

Example 4: TCP Out-of-Order Packets

Symptom: Poor application performance.

What to Look For: Filter for tcp.analysis.out_of_order. Out-of-order packets can signal network issues causing packets to take different paths, potentially leading to jitter in real-time applications.

Example 5: TCP Zero Window

Symptom: Connection stalls.

What to Look For: Use tcp.analysis.zero_window to find zero window size announcements. This indicates the receiver’s buffer is full and cannot accept more data, a sign of overwhelmed receiving applications or under-resourced hosts.

Example 6: Excessive Broadcast Traffic

Symptom: Network slowdown.

What to Look For: Identify broadcast traffic using eth.dst == ff:ff:ff:ff:ff:ff. High levels of broadcast traffic can indicate misconfigured devices or services flooding the network.

Example 7: ICMP Destination Unreachable

Symptom: Inability to connect to specific hosts or services.

What to Look For: Filter ICMP traffic with icmp.type == 3 to find “Destination Unreachable” messages, which can help identify routing issues or firewalls blocking traffic.

Example 8: SYN Flood Attack

Symptom: Denial of service.

What to Look For: Use tcp.flags.syn == 1 and tcp.flags.ack == 0 to filter for SYN packets. A high volume of SYN packets without corresponding ACKs may indicate a SYN flood DDoS attack.

Example 9: Misconfigured Firewall or ACLs

Symptom: Legitimate traffic is dropped.

What to Look For: Analyze the TCP three-way handshake (SYN, SYN-ACK, ACK) using tcp.flags.syn == 1 and subsequent filters. If the handshake does not complete or if there’s a sudden reset after the handshake, it might indicate firewall rules or ACLs prematurely blocking or dropping connections.

Example 10: SSL/TLS Handshake Failures

Symptom: Secure websites or services are inaccessible.

What to Look For: Filter for SSL/TLS handshakes with ssl.handshake or tls.handshake. Look for handshake failure messages or alerts that indicate issues with SSL/TLS negotiations, such as expired certificates or cipher suite mismatches.

=======================

PCAP files can provide the necessary data to understand what’s happening on the network. Below are complex examples illustrating how to use Wireshark to diagnose network slowness, including what logs to search for and how to interpret them.

Example 1: Diagnosing High Latency in Network Communication

Symptom: Users report slow application response times when accessing services hosted on a remote server.

Wireshark Analysis:

1. Capture Filter: Start with a capture filter for the server’s IP address to limit the amount of captured data. For example, host 192.168.1.50.
2. Time Analysis: After capturing the data, use the Time Delta from Previous Displayed Frame column to analyze the time between packets in a TCP conversation. Look for large gaps between the SYN, SYN-ACK, and ACK packets of a TCP session, indicating high latency.
3. TCP Stream: Follow a TCP stream (Right-click > Follow > TCP Stream) to examine the sequence of packets within a single connection. Significant delays between request packets and their responses suggest network or server latency issues.

Solution: If high latency periods correlate with specific network paths or devices, investigate further for potential bottlenecks or misconfigurations on those devices. If the server itself consistently shows delayed responses, the server’s performance or application efficiency may need optimization.

Example 2: Identifying Packet Loss

Symptom: VoIP calls and video conferences are choppy, suggesting packet loss.

Wireshark Analysis:

1. Capture Filter: Use a capture filter to isolate traffic to the affected service, e.g., ip.addr == 192.168.1.100 && udp for a VoIP server at 192.168.1.100.
2. Expert Infos: Open the Analyze menu and select Expert Infos. Look for warnings or errors indicating retransmissions or out-of-order packets, common signs of packet loss.
3. Sequence Numbers: In the UDP or TCP analysis, closely examine the sequence numbers for gaps which indicate lost packets, particularly in streams where you expect continuous or sequenced delivery, like RTP (Real-time Transport Protocol) streams in VoIP.

Solution: Consistent packet loss may indicate a congested network link, faulty networking hardware, or issues with the service provider. Addressing the specific path or equipment experiencing loss is essential for resolution.

Example 3: Troubleshooting TCP Retransmissions and Window Size Issues

Symptom: File transfers and database queries are significantly slower than expected.

Wireshark Analysis:

1. TCP Analysis: Use the filter tcp.analysis.retransmission to find retransmitted packets. Frequent retransmissions can significantly impact performance and indicate either network congestion or an unreliable connection.
2. Window Size Analysis: Look at the TCP window size (tcp.window_size_value and tcp.analysis.zero_window) throughout a connection. A zero or consistently small window size indicates the receiver cannot process incoming data quickly enough, causing the sender to pause data transmission.

Solution: For retransmissions due to congestion, consider increasing bandwidth, implementing QoS (Quality of Service), or optimizing traffic patterns. For window size issues, tuning TCP window scaling options on the server or client may help, as well as investigating the receiving application’s performance.

Example 4: Analyzing DNS Delays

Symptom: Websites take a long time to start loading.

Wireshark Analysis:

1. DNS Filter: Use dns to filter DNS traffic. Look for delays between DNS requests and their corresponding replies. Long delays or failed queries (No such name) can significantly impact initial connection times.
2. Transaction ID Matching: Ensure the DNS request and response transaction IDs match, confirming that delays are not due to mismatched or lost queries.

Solution: Persistent DNS delays may necessitate switching to a faster DNS server, optimizing DNS caching, or investigating internal DNS server performance issues.

Introduction to Proxies:

Proxies are intermediary servers that act on behalf of clients to fulfill various network requests. They are commonly used to provide enhanced security, privacy, and performance for clients accessing resources on the internet or within an internal network. Two primary types of proxies are forward proxies and reverse proxies. Let’s dive deeper into each with examples:

1. Forward Proxy:

Definition: A forward proxy sits between a client (such as a user’s device) and the internet. When the client makes a request to access a resource on the web, the forward proxy forwards the request to the target server on the client’s behalf. The target server sees the request as coming from the proxy server, not the original client.

Use Cases:

• An organization’s internal network may use a forward proxy to control and monitor internet access for its users.
• In countries with internet censorship, users may use forward proxies to bypass restrictions and access blocked content.

Example:

Suppose a user with IP address 192.168.1.100 wants to access https://www.example.com. The user’s device is configured to use a forward proxy with IP address 10.0.0.1. When the user initiates the request, the following process occurs:

1. The user’s device sends the request to the forward proxy server (10.0.0.1).
2. The forward proxy forwards the request to the target server https://www.example.com.
3. The target server responds to the proxy with the requested content.
4. The proxy server sends the content back to the user’s device.

2. Reverse Proxy:

Definition: A reverse proxy sits between the internet (clients) and backend servers. When clients request resources from a specific server, the reverse proxy forwards those requests to the appropriate backend server on behalf of the clients. The backend server’s identity remains hidden from the clients.

Use Cases:

• Load balancing: A reverse proxy can distribute incoming client requests across multiple backend servers to improve performance and ensure high availability.
• Security: A reverse proxy can protect backend servers by acting as a single entry point, shielding them from direct exposure to the internet.

Example:

Suppose a client wants to access https://www.example.com. In this scenario, https://www.example.com is served by multiple backend servers (Backend Server 1, Backend Server 2, etc.). The client’s request goes through the reverse proxy, and the following process occurs:

1. The client sends the request to the reverse proxy server.
2. The reverse proxy server forwards the request to one of the backend servers (e.g., Backend Server 1).
3. Backend Server 1 processes the request and sends the response back to the reverse proxy.
4. The reverse proxy server sends the response back to the clien

When to Use Forward Proxy:

1. Internet Access Control: In organizations, a forward proxy can be used to control and monitor internet access for employees. It allows administrators to enforce internet usage policies, block access to specific websites, and prevent users from accessing malicious or inappropriate content.
2. Bandwidth Optimization: Forward proxies can cache frequently requested content, reducing the need to download the same data repeatedly. This helps save bandwidth and speeds up internet access for users.
3. Anonymity and Privacy: Users in restrictive countries or environments may use forward proxies to access the internet anonymously, bypassing censorship and preserving privacy.
4. Security Scanning: Forward proxies can be used to scan incoming web traffic for malware, viruses, or other security threats before allowing access to the client.

Example of Forward Proxy:

Suppose an organization has a forward proxy server deployed at proxy.example.com. All internal user devices are configured to use proxy.example.com as their internet gateway. When users access websites like www.example.com, their requests are first sent to proxy.example.com, which then forwards the requests to the respective web servers. This way, the organization can control and monitor internet usage for its employees.

When to Use Reverse Proxy:

1. Load Balancing: Reverse proxies distribute incoming client requests across multiple backend servers, ensuring efficient resource utilization and preventing overload on individual servers.
2. SSL Termination: Reverse proxies can handle SSL/TLS encryption and decryption, relieving backend servers from the resource-intensive SSL processing.
3. Caching and Content Delivery: Reverse proxies can cache and serve static content, reducing the load on backend servers and improving content delivery speed.
4. Application Firewall: Reverse proxies can act as application firewalls, inspecting and filtering incoming traffic to protect backend applications from attacks.

Examples of Reverse Proxy:

1. Load Balancing: Suppose a high-traffic website (www.example.com) is hosted on multiple backend web servers (Web Server 1, Web Server 2, etc.). A reverse proxy like proxy.example.com sits in front of these backend servers and distributes incoming client requests across them, ensuring even distribution of load.
2. SSL Termination: When clients access a secure website (https://secure.example.com), the SSL/TLS handshake and encryption/decryption can be handled by the reverse proxy, while the actual application servers only receive decrypted requests.
3. Caching and Content Delivery: A reverse proxy can cache and serve static files like images, scripts, and stylesheets. When a client requests these resources, the reverse proxy delivers them directly, reducing the load on backend servers and improving website performance.
4. Application Firewall: The reverse proxy can inspect HTTP requests and responses for malicious content or known attack patterns, protecting backend applications from common web application attacks.

Conclusion:

Forward proxies and reverse proxies serve as intermediaries in different scenarios. A forward proxy sits between clients and the internet, while a reverse proxy sits between the internet and backend servers. Both types of proxies play crucial roles in enhancing security, privacy, and performance in various network environments. Understanding their differences and use cases helps network administrators design robust and secure proxy solutions for their organizations.

In SolarWinds, the “engine ID” refers to a unique identifier assigned to each monitored network device or SNMP agent within the network. It is an essential component of the SNMP (Simple Network Management Protocol) system, which is used for network monitoring and management.

When SolarWinds collects data from network devices using SNMP, it uses the engine ID to identify and differentiate between different SNMP agents. Each SNMP agent (device) is assigned a specific engine ID, which acts as a unique identifier similar to an IP address or hostname.

The engine ID is exchanged during the SNMP discovery process when SolarWinds first communicates with a device. Once the engine ID is known and mapped to the device, SolarWinds can effectively manage and monitor the device using SNMP.

The engine ID is a critical piece of information for SNMP communication, as it helps ensure that SNMP data is correctly associated with the correct device. It helps prevent data mixing or misinterpretation when multiple devices are sending SNMP data to SolarWinds.

If the engine ID of a device is not configured or is unknown to SolarWinds, SNMP communication and monitoring for that device may not function correctly. This can result in errors like “engine ID that was not configured” or incorrect data representation within SolarWinds.

To resolve such issues, the correct engine ID must be configured for each SNMP-enabled device in SolarWinds to establish a proper association between the device and the SNMP data collected by the monitoring system.

The error message “engine ID that was not configured” in SolarWinds is related to SNMP (Simple Network Management Protocol) configuration. This message indicates that the SolarWinds server received an SNMP trap or poll from a device with an unknown or unconfigured engine ID. An engine ID is a unique identifier used by SNMP to identify the SNMP entity (device) in the network.

Troubleshooting this issue typically involves capturing and analyzing SNMP traffic using PCAP (Packet Capture) analysis. Below is an example of how you can perform PCAP analysis to troubleshoot the “engine ID that was not configured” error in SolarWinds:

Step 1: Enable SNMP Trap Debugging in SolarWinds:

1. Log in to the SolarWinds server.
2. Open the SolarWinds Orion Web Console.
3. Go to “Settings” > “All Settings.”
4. Under “Product Specific Settings,” click on “SNMP Trap Service Settings.”
5. In the “SNMP Trap Debugging” section, enable “Log packets to disk for later analysis.”

Step 2: Capture SNMP Traffic Using PCAP:

1. On the SolarWinds server, use a PCAP capture tool like Wireshark to capture SNMP traffic:

tcpdump -i <interface> -s 0 -w snmp_traffic.pcap udp port 161

1. Replace <interface> with the network interface where SNMP traffic is expected (e.g., eth0).
2. Leave the PCAP capture running for a sufficient time to capture SNMP traffic that triggers the “engine ID that was not configured” error in SolarWinds.

Step 3: Reproduce the Issue:

During the time you are capturing SNMP traffic, trigger the SNMP trap or poll that causes the “engine ID that was not configured” error in SolarWinds. This could be done by rebooting a device, sending a test SNMP trap, or polling a specific OID.

Step 4: Stop the PCAP Capture:

Once you have reproduced the issue or captured enough SNMP traffic, stop the PCAP capture by pressing Ctrl+C.

Step 5: Analyze the PCAP File:

Open the captured PCAP file (snmp_traffic.pcap) using Wireshark or any other PCAP analysis tool.

1. Filter SNMP traffic: Apply a filter to display only SNMP traffic by entering udp.port == 161 in the Wireshark filter box.
2. Look for SNMP traps or polls: Analyze the captured SNMP traffic to identify SNMP traps or polls that have an unknown or unconfigured engine ID.
3. Check for SNMP engine IDs: Look for the “SNMP Engine ID” field in the SNMP packets. Compare these engine IDs with the configuration in SolarWinds to identify the devices with unknown engine IDs.

Step 6: Configure SNMP Engine IDs in SolarWinds:

Once you have identified the devices with unknown engine IDs, you can configure these engine IDs in SolarWinds:

1. Log in to the SolarWinds Orion Web Console.
2. Go to “Settings” > “All Settings.”
3. Under “Product Specific Settings,” click on “Manage SNMP Credentials.”
4. Edit the SNMP credentials for the affected devices and enter the correct engine IDs.

Step 7: Verify and Monitor:

After configuring the correct engine IDs in SolarWinds, verify that the “engine ID that was not configured” error no longer occurs. Monitor SNMP traps and polls to ensure the issue is resolved.