cnWave IP Network Planning
cnWave is a Layer 3, routed IPv6 network technology where cnWave nodes incorporate an RF radio and an IP router. This section focuses on the IP routing aspect of cnWave nodes. cnWave uses Border Gateway Protocol (BGP) as the exterior gateway protocol (EGP) and Open/R as the interior gateway protocol (IGP).
The network prefix (also called Seed prefix) in cnWave is usually a /56 allocation, which is further divided into /64 prefixes to be assigned to individual nodes. The network prefix bounds the maximum possible number of radios in the deployment. A /56 network, for example, will yield 256 distinct /64 allocations.
Where possible, it is advisable to choose a network prefix space much larger than the anticipated number of deployed nodes (e.g. to account for future network expansion), and which yields at least twice as many allocations as the number of nodes (e.g. to support network-wide address reassignment). Below are some commonly used IPv6 network prefixes used in cnWave.
|Prefix||Max Number of Radios|
Each cnWave node is assigned an IPv6 /64 prefix as the loopback interface. This loopback interface address is used by the E2E controller to address the node. Prefix allocation to the nodes are centrally done through the E2E controller. The /64 address prefix also enables the node to address downstream CPEs using Stateless Auto Configuration (SLAAC) via router advertisements.
While cnWave is a wireless technology, there must be at least one wired cnWave PoP node that connects to an upstream IPv6-enabled network. cnWave PoP nodes peer with an upstream router using BGP. In the BGP implementation, the PoP node advertises the cnWave network prefix (or a subset of the prefix) and expects to receive a default route from the upstream router. Upon receiving this default route, the cnWave PoP advertises the default route in the Open/R protocol. This ensures that the rest of the nodes in the network have an egress path to reach upstream networks. When the network consists of single PoP, static routing option can be used (instead of BGP). Upstream router’s IP address can be manually configured in the PoP as gateway address and static route can be added in the router.
cnWave networking has two limitations:
The subnet size of the cnWave PoP radio and the upstream router must be /64, as variable length subnetting is not supported.
All cnWave PoP nodes must be connected to the same Layer 2 broadcast domain. This allows cnWave PoP nodes to forward traffic to other cnWave PoP nodes via a wired connection when the routing path of the other PoP node is closer to the traffic’s destination. This concept is known as tromboning, because the traffic enters a PoP node and then leaves toward another PoP node.
Layer 2 Bridging
While cnWave is a IPv6 layer 3 based technology, IPv4 is supported with the use of Layer 2 tunnels. When L2 is enabled, each node automatically forms a Layer 2 tunnel to the PoP node and transports user traffic. Downstream CPEs obtain IP address from the DHCP server running in the operator’s network.