Dynamic Host Configuration Protocol for IPv6 (DHCPv6) is just that: a protocol that can be used for host configuration, defined in RFC 8415. In this post I will introduce some basics of the protocol. DHCPv6 protocol A DHCPv6 message for client-server conversation consists of message type (1 byte), transaction ID (3 bytes) and variable number […]
In my earlier posts I have shown the Microsoft Windows DHCP server failover configuration behavior where the servers independently decide who will answer to which DHCP clients, using a hashing algorithm based on client hardware address field (usually containing MAC address) in the DHCP packets. In this post I will show how the failover system […]
One of the built-in security features in Zabbix is TLS (Transport Layer Security) support for external connections. This means that when your distributed Zabbix proxies or Zabbix agents connect to the Zabbix server (or vice versa), TLS can be used to encrypt all the connections. When the connections are encrypted, third parties cannot read the […]
In a network I was faced with exceptionally large number of IP address DHCP leases for short-time usage. Even though the lease duration was set as relatively short, the DHCP server still occasionally complained about the DHCP scope being full, being unable to assign an IP address to a client. Let’s demonstrate the situation with […]
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 […]
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 […]