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: […]
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 […]
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 […]
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 […]
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 […]
Short one: How to make a serial console server (or terminal server) with a Raspberry Pi and USB-serial adapter. Connect the serial port to whatever device you want to use for testing, and use any telnet-compatible client (like PuTTY) to connect to your Pi’s IP address and the configured port (2000, 3000 or 4000 in […]
Let’s see how the Zabbix active agent autoregistration works in the communication. I have configured the Zabbix agent (version 6.2.3) on the Linux host at 192.168.7.17 with this configuration: ServerActive=192.168.7.15 Hostname=Test-agent After restarting the agent, the Zabbix server (version 6.2.3) at 192.168.7.15 logged immediately in /var/log/zabbix/zabbix_server.log: cannot send list of active checks to “192.168.7.17”: host […]
I’ve done countless troubleshooting sessions so that I’m having Wireshark open with a relevant capture file and either I’m showing my findings to the other participants or doing straight up live packet analysis. Sometimes the sessions are followed up with questions about how did I actually have Wireshark configured because it looked different on their […]
This is a memo and reminder about the routing limitations that I stumbled into when working with Nexus 9000 series switches running NX-OS. Feature Limitation Link to documentation PBR You cannot configure PBR on port-channel subinterfaces Interfaces configuration guide for 9.3(x) QoS You cannot configure QoS on port-channel subinterfaces QoS configuration guide for 9.3(x) QoS […]
In this post I’ll discuss a reality that is often overlooked when talking about using cloud services: Network latency matters. Here is the test network: On Your Marks Let’s first imagine that the hosts HostA and HostB are near each other, like in the same data center. The latency between the hosts is negligible: markku@HostA:/mnt$ […]