Field notes
Blog
Articles on networking, security and the internet.
Results: 54
Latency and jitter: why averaging isn't enough
Low average latency alone does not guarantee that voice calls will be uninterrupted. Changes in packet latency over time also affect the experience.
Bufferbloat: why does ping increase during upload?
If your connection is fast but the game or conversation crashes when the backup starts, examine the latency under load. The issue may not just be the amount of bandwidth.
How to measure packet loss and avoid misinterpretation?
Packet loss percentage is only meaningful with the target, duration and number of samples of the test. Losing one in four pings does not prove a 25 percent long-term loss.
How to read Traceroute stars and changing paths?
Asterisks in Traceroute output do not always indicate that the connection was lost at that point. Devices on the road may treat diagnostic messages differently.
MTU issue: why does the large transfer get stuck while the small request is running?
Partial opening of a page or major transmission interruption over VPN may be related to packet size. Conduct MTU probe separate from DNS and service access.
Inventory with SNMP: what information comes from where?
Managed network devices can present identity, interface, and operational information over SNMP. When using this data, the access authority and the source of the information must be visible.
Choosing the right SNMPv3 security levels
Two installations said to use SNMPv3 may not have the same security features. It is necessary to separately check the level of authentication and confidentiality.
Does the MAC forwarding table prove physical connectivity?
The MAC table on the switch can indicate which direction a device is located. However, not every record refers to a single device plugged directly into that port.
Visibility and access difference in ONVIF camera discovery
Just because a camera appears in the discovery list does not mean that the video stream can be opened. Treat discovery, device information, and media access as separate phases.
RTSP port open: is this device a real camera?
Precisely determining the device type from an open media port may produce inaccurate inventory. Use the port number as a starting clue and look for independent evidence.
HTTP 401, 403 and 404: network failure or application response?
Seeing an error page in the browser does not mean that the network connection cannot be established. The HTTP status code provides valuable information about what stage the request has reached.
Distinguish TLS certificate error from network problem
The browser may show a certificate error even though a TCP connection to the server can be established. In this case, the name, time, trust chain and service configuration should be examined.