What is end-of-row switch?

Answer 1

End-of-row switching is the most traditional approach, where a single large chassis-based switch such as the Cisco Catalyst® 6500 Series Switch is used to support one or more racks. Because the Catalyst 6500 Series can support considerable density, this approach is usually the most cost-effective in terms of delivering the highest level of switch and port utilization, especially when coupled with the rich set of network virtualization services available in the Catalyst 6500 Series. Because it also supports a wide variety of service modules, the Catalyst 6500 Series also simplifies pushing security and application networking services into the access layer, which can be a significant advantage from a compliance and security perspective.

The end-of-row approach is also the most server-independent, so it provides maximum flexibility to support a broad range of servers. In certain scenarios, end-of-row switching can provide performance advantages, because two servers that exchange large volumes of information can be placed on the same line card to take advantage of the low latency of port-to-port switching (as opposed to card-to-card or switch-to-switch, which will be slower).

The primary disadvantage of end-of-row switching is the need to run cable back to the switch. Assuming every server is connected to redundant switches, this cabling can incur considerable costs and add operational complexity. Also, the physical volume of the cable wastes valuable rack space and may impede efficient equipment cooling. And, going forward, any significant move to 10 Gigabit Ethernet for servers will present some challenges.

Top-of-rack switching is a viable choice for dense 1 rack unit (1RU) server environments. In this approach the 1RU Cisco Catalyst 4948 Switch is placed at the top of the rack and all the servers in the rack are cabled to the switch, which then has one uplink to the aggregation layer. In some instances a pair of Catalyst 4948 Switches are used for high-availability purposes. This approach significantly simplifies cable management and avoids the rack space and cooling issues of end-of-row switching. This approach also provides some architectural advantages such as fast port-to-port switching for servers within the rack, predictable oversubscription of the uplink and smaller switching domains (one per rack) to aid in fault isolation and containment.

The common challenge with the top-of-rack approach is suboptimal port utilization - not enough servers to fill the switch. One option is to put one top-of-rack switch server in an adjacent rack: this preserves the advantages of the top-of-rack switch while increasing port utilization. However this approach should be done sparingly and with good discipline to avoid devolving into a poorly executed end-of-row arrangement. Finally, with a top-of-rack approach, attention must be paid to ensure that commonly used or high-volume data pathways do not end up spanning multiple racks and thus multiple switches.