Oct 09 2013

A Routing and Switching Technology Cheat Sheet

Get familiar with some of the newest networking terms IT admins must know.

Routers and switches are filled with technologies, some of which matter — and some of which don’t.

What follows are some of the newest terms network managers will run into when they’re evaluating products and building their networks.

IP Broadcast and Multicast Routing

Certain protocols, such as telephony management, multimedia streaming, file sharing and printer protocols, were designed for small LANs and depend on multicast/broadcast packet routing. In enterprises with multiple subnets, these protocols won’t work across subnets without specific routing support, as routers typically block broadcast and multicast. Network managers should carefully manage IP multicast routing in campus environments by applying consistent policy and trimming inappropriate traffic.

Bonjour and Multicast Domain Name System (mDNS)

Apple has popularized Bonjour, its implementation of a series of zero-configuration networking protocols, including mDNS for device discovery. As BYOD and mobility encourage staff to use mobile devices, protocols such as mDNS/Bonjour are used to find video devices, printers and other related peripherals. Bonjour isn’t appropriate across large networks, so network managers will need to offer compatible technologies (such as multicast DNS for service discovery) to provide a seamless experience.

Layer 3 Switching

Many switch companies have added IP routing to their switches, but they’re using the term Layer 3 switching instead of the more traditional routing. Generally, this term implies that the router has no dynamic routing capabilities and can handle only simple static routes without other common router features. It’s also used to avoid going head-to-head with Cisco and Juniper Networks by creating a new product that isn’t called a router , yet is one.

Layer 4 and Layer 7 Switching and Routing

Most IP routing happens at Layer 3 , the IP layer. However, many network applications, such as traffic interception for security purposes (URL filters, web proxies), WAN optimization and load balancing require routing above the IP layer. These requirements are generally specialized but are increasingly common at network edge (security/optimization) and in front of server farms (load balancing). Often, specialized hardware is used for Layer 7 routing, but most enterprise routers can handle some types of Layer 4 routing using either Cisco’s Web Cache Communication Protocol (WCCP) or more generic policy-based routing (PBR).

Cut-Through Switching and Routing

A switch or router often can make a routing or forwarding decision based on the first few octets of a received packet, which contain the destination MAC or IP address. This allows the switch/router to start transmitting the packet before it has been completely received, reducing latency compared with more traditional store-and-forward techniques that receive the entire packet before starting to forward it. Cut-through is most important in very-high-performance networks where every nanosecond of latency matters, making it a common technique at network cores but unusual in WAN and user access environments.

WAN Path Selection

WAN environments often have multiple outbound links. In normal WAN IP routing, all packets between two points over a stable network will use the same path. When traffic is concentrated between two sites, this can cause saturation of one link, while the other is underutilized.

WAN path selection (also called performance-based routing) can be used to balance traffic across multiple links by categorizing applications based on performance requirements, using the faster and more reliable path for applications that require higher performance or lower latency, while moving lower priority traffic to an alternative path. WAN path selection is a new area for many network vendors and enterprises. Results have been mixed; some network managers are fans, while others are disappointed.

To learn more best practices, insights and strategies on routing and switching, read our "Ultimate Guide to Routing and Switching."