In DHCP servers you can configure IP address reservations, meaning that you statically configure the IP addresses that you want the specific DHCP clients to get. This is sometimes desirable when you know your devices and want to ensure that their DHCP-assigned IP addresses won’t change, because of, you know, reasons. (Printers may or may […]
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 […]
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 […]
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 […]
Simple example how to send a UDP packet with Scapy in a Python application: When using sendp() it is necessary to construct the full packet, starting from L2 Ethernet frame. The “/” operator is cleverly used when combining the layers of the packet.
At some point I tried to configure Juniper SRX100 with DHCPv6 server, with no luck. The configurations didn’t just work. I gave up at that time, but returned to the matter some days ago. I realized something in Junos DHCP configurations: people are talking about “old” and “new” ways to configure DHCP server and client […]