y LA Primary Up/down Up/up .1 VIP EIGRP 100 VIP .1 NY-Backup LA-Backup Figure 13-6. Better failover design using EIGRP Nexus and HSRP As with many protocols on Nexus, you must first enable the HSRP feature with the feature hsrp command. NX-OS adds some functionality to HSRP when you're using vPCs. In short, when a packet is received on a routed (nonswitch) port and is destined for the HSRP VIP con- figured on the router, the packet will terminate on that router, even if it is not the active HSRP router. Packets received on Layer-2 interfaces will be forwarded to the active router. Why is this important? First, this will help to eliminate traffic on interrouter links. Second, if you're not aware of this behavior, you may go quite mad trying to figure out where traffic is flowing when you think it works the traditional way. You have been warned. vPCs between two Nexus switches will forward traffic through both the active and standby routers. Cisco documentation recommends that you configure the HSRP active router to be the same device as the primary vPC peer. GLBP (Gateway Load Balancing Protocol) is similar to HSRP and VRRP, but with the addition of load balancing between group members. With HSRP and VRRP, there is only one active member, while the other member or members forward no traffic. With GLBP, each member may forward traffic and can even be weighted. Weighting the gateway members allows you to have, for example, three gateways active with 50% of traffic going to one and 25% going to each of the other two. You can have a maximum of 1,024 GLBP groups per router interface with up to four virtual forwarders per group. Let's look at an example. Figure 13-7 shows a simple network containing five hosts with three routers. Each of these three routers will participate in GLBP, and we will actively forward traffic through all three. We'll configure R1 to take 50% of the load, while R2 and R3 will take 25% each. bb.bb.bb.bb.bb.bb aa.aa.aa.aa.aa.aa CC.CC.CC.CC.CC.CC VIP:. .1 10.0.0.0/24 1.105 Host-1 Host-2 Host-3 Hos