An advanced systems administration and networking series covering network bonding, firewalling, DNS resolution, enterprise storage, web services, and security hardening.
IPv6 is not an incremental upgrade to IPv4. It is a replacement for the network layer of the internet, designed because IPv4’s 32-bit address space could not support the number of devices that would eventually need to connect. The exhaustion was not speculative. On February 3, 2011, IANA allocated the final five /8 blocks from…
IPv6 addresses are 128-bit identifiers, four times the length of their IPv4 counterparts. That length is not merely a larger number; it is the space in which the protocol’s addressing architecture is carved. Every IPv6 address belongs to one of three types—unicast, anycast, or multicast—and within those types, specific prefixes define scope and purpose. Unlike…
IPv6 configuration on Linux is not a single command. It is a sequence: verify the kernel has IPv6 enabled, assign addresses to interfaces, enable forwarding if the host is a router, and distribute prefixes to clients if the network uses stateless autoconfiguration. Every modern Linux kernel enables IPv6 by default and assigns a link-local address…
Static routing is the manual configuration of a path through a network. An administrator tells the kernel: “To reach this destination network, send packets to this gateway, or out this interface.” The kernel stores that instruction in its routing table, and every packet destined for that network follows it until the route is removed or…
Configuration is where static routing theory becomes kernel state. The previous chapter established why static routes exist and how the kernel selects them by longest prefix match. This chapter is the operational counterpart: the exact commands to add, verify, replace, and remove routes, the flags that handle gateways outside connected subnets, and the persistence mechanisms…
The default gateway is the route of last resort. When the kernel examines a packet’s destination and finds no matching entry in the routing table, it forwards the packet to the default gateway. This single route is what connects a host or a local network to everything beyond its directly attached subnets. Without it, the…
Classic routing makes a decision based solely on the destination address. A packet arrives, the kernel searches its routing table for the longest matching prefix, and forwards the packet accordingly. This model assumes that every packet destined for the same network should follow the same path. Policy routing breaks that assumption. It allows the administrator…
The previous chapter established the routing policy database and the rule selectors that drive it. This chapter is the operational counterpart: creating custom routing tables, populating them with routes, writing rules that direct specific traffic to them, and ensuring the entire configuration survives a reboot. A single policy rule is a proof of concept. A…
A Linux bridge is a software switch. It connects two or more network interfaces at Layer 2, forwarding Ethernet frames between them based on MAC addresses, not IP addresses. The bridge itself becomes a logical interface—typically br0—that carries an IP address, while the physical interfaces attached to it become ports, stripped of their own addresses…
The previous chapter established what a bridge is: a software switch that forwards frames between ports based on a learned MAC address table. This chapter is the operational sequence. Creating a bridge is a single command; making it work correctly requires a specific order of operations, and making it persist requires the correct configuration for…