Chapter 5. Rack planning 143Table 5-10 Part number for Rear Door Heat eXchanger for IBM 42U 1100 mm rackFor more information, see Rear Door Heat eXchanger V2 Type 1756 Installationand Maintenance Guide, which is available at this website:http://www.ibm.com/support/entry/portal/docdisplay?lndocid=migr-50895755.6 Top of rack switchesThe IBM NeXtScale System does not include integrated switching in the chassis,unlike IBM BladeCenter or IBM Flex Systems. This was done to maximize themodularity and flexibility of the system and prevent any chassis-level networkingcontention. The IBM Intelligent Cluster offering includes various switches fromIBM System Networking and others that can be configured and ordered as anintegrated solution. People that are building solutions (including NeXtScalesystems) can combine them with switches of their own choosing. In the followingsections, we describe the switches that are available from IBM.5.6.1 Ethernet switchesThe IBM NeXtScale System features forward-facing cabling. To connect cablesfrom the NeXtScale servers to Ethernet switches, it is easiest to mount theswitches in the racks with the switch ports facing the front of the racks as well.It is important that the cooling air for the switches flow from the front (port side) ofthe switch to the rear (non-port side). The switches that are listed in Table 5-11on page 144 meet this criteria. Switches that are cooled from rear to front can beused, but these must be mounted facing the rear of the rack, and all the cablesfrom the servers are routed from the front of the rack to the back to connect.Part number Description175642X Rear Door Heat eXchanger for IBM 42U 1100 mm Enterprise V2Dynamic RacksNote: There is no rule that smaller rack mountable switches (typically 1U or2U) must be mounted in the top of a rack, but “top-of-rack” is the commonname they were given. This is in contrast to larger switches that are deployedfor rows of rack-mounted servers, which are referred to as “end-of-row”switches; or the often large, modular switches, which also often containrouting functionality, which are commonly called “core switches”.
