This post shows how Windows Server DHCP service deals with lease expirations and deletions.
About Windows DHCP Server Lease Expirations
Network Interface Name Sorting in Python
Evergreen problem in sorting strings: How do you implement human-expected ordering when the strings have varying-length numbers in them? Prime example in the networking world is network interface naming in various devices. Example: >>> interfaces = [“1/1/1”, “1/1/2”, “1/1/10”, “1/1/11”, “1/1/10.32”, “1/1/10.311”, “1/1/10.312”, “eth-1/1/1.1”, “eth-1/1/1.2”, “eth-1/1/1.10”]>>> print(“\n”.join(sorted(interfaces)))1/1/11/1/101/1/10.3111/1/10.3121/1/10.321/1/111/1/2eth-1/1/1.1eth-1/1/1.10eth-1/1/1.2>>> That’s not ideal as the default string sorting […]
Troubleshooting Zabbix Agent with Wireshark
A user has a Zabbix agent that collects the used disk space information on a host. The item interval is one minute: However, the user complains that Zabbix fails to collect to data appropriately as the graph has empty areas with occasional dots: In Zabbix implementations with very high NVPS (new values per second) this […]
Change History for Zabbix Protocols
All the information on this page is gathered from the official Zabbix documentation about the protocols and the upgrade notes. I’m using this information to assist with the Zabbix protocol dissector development in Wireshark, thus not all possible protocol change details will be documented here but mostly only those that affect the dissector. Server-proxy data […]
Lease Time One Hour with Windows DHCP Servers
Interesting question: Why does Windows DHCP server first assign me a lease for only one hour, and after that extend it to one day (or whatever was actually configured in the DHCP scope)? First, let’s see that it really happens as described. Replicating the setup from my previous DHCP posts, I have here two VLANs: […]
DHCP Relay, Part 3: Two Relays, Two Servers
This is part three of the DHCP relay mini-series: In this setup we still have two DHCP servers in load balancing configuration, but we also have two routers in the DHCP client subnet acting as DHCP relays. The routers are running HSRP (Hot Standby Routing Protocol) for first-hop routing redundancy, but it’s really not relevant […]
DHCP Relay, Part 2: One Relay, Two Servers
This is part two of the DHCP relay mini-series: In this setup there are two DHCP servers in load balancing configuration, so the DHCP relay has been configured with two DHCP server IP addresses where to forward the DHCP packets to: 10.0.41.10 and 10.0.41.11. The methodology from the first post is followed: the DHCP client […]
DHCP Relay, Part 1: One Relay, One Server
This is part one of the DHCP relay mini-series: In VLAN 60 there is a DHCP (Dynamic Host Configuration Protocol) client that will try to get an IP address from a DHCP server. There is no DHCP server in VLAN 60, but there is a DHCP relay configured on the router, and it will forward […]
Tools for Debian Packages
Debian has been my primary Linux distribution of choice since 2003. That’s twenty years! How time flies! I haven’t ever worked as full-time server administrator but running and operating various kinds of systems have always been part of my skills, and it has made it possible for me to leverage wide range of tooling required […]
Capturing Packets on Windows with Packet Monitor (Pktmon)
As https://learn.microsoft.com/en-us/windows-server/networking/technologies/pktmon/pktmon puts it: Packet Monitor (Pktmon) is an in-box, cross-component network diagnostics tool for Windows. It can be used for packet capture, packet drop detection, packet filtering and counting. Nice thing about it is that it is present by default on all modern Windows versions, so you can do a quick packet capture when […]