Intersubnet

Intersubnet refers to communication between devices on different IP subnets. In typical IP networks, subnets partition address space to improve management, security, and performance. Because hosts on different subnets are separated at layer 3, intersubnet communication requires routing through a router or layer-3 switch.

How it works: Each subnet defines a range via its network address and subnet mask (or prefix in IPv6). Hosts send packets destined for other subnets to their default gateway. The gateway uses its routing table to select the next hop toward the destination, forwarding the packet across routers or layer-3 devices until it reaches the destination subnet.

Routing methods: Static routes specify fixed paths, while dynamic routing protocols such as OSPF, IS-IS, EIGRP, or BGP exchange topology information and adjust to failures or topology changes. In many networks, inter-subnet routing is performed by edge routers or multilayer switches, and it is distinct from inter-VLAN routing, which occurs inside a switch for different subnets within the same broadcast domain.

Security and design: Inter-subnet traffic is commonly filtered by access control lists or firewalls. Subnet design, route aggregation, and, where applicable, virtual routing and forwarding (VRF) help control scope and improve scalability. In IPv6, similar principles apply with prefix lengths instead of masks.

Common challenges include misconfigured subnet masks, MTU issues, asymmetrical routing, and misrouted traffic. Proper design and monitoring are essential to maintain performance, reachability, and security across subnets. Typical use cases include enterprise networks with multiple subnets per department, data centers, and multi-site WANs.