Specifications

CHAPTER 5
Implementing High Availability
There must be a physical link between distribution switches, and it should be a L2 trunk. Without that link, any traffic
between switches must go through an access switch. Additionally, failure of one of the access-to-distribution uplinks
causes packets to be dropped until the FHRP dead timer expires.
Figure 5-3 shows the recommended design when using L2 access switches. Each VLAN is local to one switch. The
FHRP Active and STP Root must still be the same switch. They are still statically configured per VLAN so that traffic
flow will be deterministic. Because the link between distribution switches is L3, there are no L2 loops. Thus no links are
blocked by STP. However, traffic does not load balance between links because each switch forwards traffic only over the
link to its HSRP Active and STP Root switch. RSTP is still used for faster convergence.
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CCNP SWITCH 642-813 Quick Reference by Denise Donohue
FIGURE 5-2
Layer 2 Access
Switches with
Distributed VLANs
STP
Blocked
Links
VLAN 10VLAN 10
L2 Trunk
L3
Distribution
L2
Access
HSRP Active
and STP Root