7.2 IP Routers

IP routers are distinguished from switches by the presence of WAN interfaces and routing services optimized for Internet or wide area connectivity. IP router products range from middling-performance small office devices to sophisticated director-class data center units. An IP router may also be an Ethernet switch within the local environment, providing layer 2 switch ports for end device attachment. Unlike an Ethernet switch, however, an IP router provides one or more wide area ports that enable attachment to a carrier service. The WAN interfaces can be Packet over SONET (POS), ATM, ISDN, frame relay, or point-to-point and can drive bandwidth ranging from T1 to OC-192c.

For basic routing functions, an IP router is not concerned with the type of IP data it is forwarding. Higher-level services can be applied to specific types of data so that, for example, voice over IP meets its delivery requirements. For layer 3 routing, calculation of best paths via the OSPF protocol and maintenance of route tables ensures that incoming packets are forwarded expeditiously to the next hop in the network.

For wide area storage applications, the main requirement for IP routers is simply that they route efficiently and impose minimal latency. A small, low-cost IP router with a single Gigabit Ethernet port and T3 WAN interface may be entirely adequate for remote tape vaulting or resource sharing from a branch office. At the data center, director-class IP routers can receive storage streams from hundreds of remote locations or drive high-performance OC-48 links for disaster recovery between the data center and one or more recovery sites.

Some IP router models also provide options for implementing IPSec over the wide area link, or multiprotocol label switching to enforce QoS requirements. These enhanced services further simplify design and implementation of storage over distance, provided that you have the budget to acquire them.