Single-Attached Router and Server

In Figure 11-6, the link between SW-A1 and SW-D2 fails. Because no connection exists between SW-D1 and SW-D2 carrying VLAN 101, and no inter-VLAN routing has been configured, Host 1 cannot communicate with the server in VLAN 401 or R2. It may seem obvious to avoid these kinds of single-attached configurations by dual attaching each router and dual attaching each server, but, often times, the responsibility of overall network administration is segmented into LAN, WAN, and application teams. In some circumstances, servers might get added without the knowledge of the LAN team, and problems do not surface unless a failure of the LAN infrastructure occurs. The next section, "Campus Design," outlines a few options to prevent such problems from occurring.