200-301 topics

200-301 topics.HSRP-activated LAN switches, which had previously been sending data frames destined for VMAC1 to router R1, must now know to send the frames to the newly activated router.To cause the switch to change the MAC address table entry for VMAC1, R2 sends an Ethernet data frame with VMAC1 as its source MAC address. The switch is informed of the source MAC address (VMAC1) as usual, but the new port points to R2. the data frame is still a LAN broadcast, so all switches are informed of the MAC table entry for VMAC1 pointing to R2. (Incidentally, this Ethernet data frame contains an ARPReply message called "unnecessary" ARP, because the router does not actually need to receive an ARPRequest first to send it.) HSRP Load BalancingThe HSRP activation/standby model means that all hosts in a subnet send their out-of-subnet packets through only one router. In other words, there is no load sharing among the routers; instead, one router handles all packets. For example, if we look back at Figure 6-5, R1 is an active router, so all hosts in the subnet send packets through R1, and none of the hosts in the subnet send packets through R2.HSRP picks different routers in different subnets as active routers to support load balancing, and most sites that need a second redundant router are usually large enough to use multiple VLANs, subnets, and sites. These two routers will be connected to all VLANs and will be the default router for each VLAN. HSRP can then be configured so that one router in each VLAN is active to balance the traffic.For example, Figure 6-7 shows a redesigned LAN that now has two hosts in each of VLAN1 and VLAN2.Both R1 and R2 are connected to the LAN, and both use a VLAN trunking and single-arm routing (ROAS) configuration. Both routers use HSRP in each subnet and support each other. However, configuring R1 is done intentionally so that it can win the negotiation and become the HSRP-active router in VLAN1, while configuring R2 is configured to become the HSRP-active router in VLAN2.Note that having each router be an HSRP-activated router in a particular subnet allows the design to take full advantage of the two-hop link between these two routers and the WAN.133 Chapter 6 Creating Redundant First-Hop RoutersTip: For designs that use a Layer 3 switch, the Layer 3 switch is the default router for the host. In this use case, the HSRP configuration is performed on the Layer 3 switch. Figure 6-7 shows an alternative, using a Layer 2 switch in the UKN, which uses VLAN trunking on the router.VLAN 1 subnet