Which two of these practices are considered to be best practices when designing the access layer
for the enterprise campus?(Choose two.)
A.
Implement all of the services (QoS, security, STP, and so on) in the access layer, offloading the
work from the distribution and core layers.
B.
Always use a Spanning Tree Protocol; preferred is Rapid PVST+.
C.
Use automatic VLAN pruning to prune unused VLANs from trunked interfaces to avoid
broadcast propagation.
D.
Avoid wasted processing by disabling STP where loops are not possible.
E.
Use VTP transparent mode to decrease the potential for operational error.
Explanation:
When designing the building access layer, you must consider the number of users or ports
required to size up the LAN switch. Connectivity speed for each host should also be considered.Hosts might be connected using various technologies such as Fast Ethernet, Gigabit Ethernet, or
port channels. The planned VLANs enter into the design.
Performance in the access layer is also important. Redundancy and QoS features should be
considered.
The following are recommended best practices for the building access layer:
• Limit VLANs to a single closet when possible to provide the most deterministic and highly
available topology.
• Use Rapid Per-VLAN Spanning Tree Plus (RPVST+) if STP is required. It provides the faster
convergence than traditional 802.1d default timers.
• Set trunks to ON and ON with no-negotiate.
• Manually prune unused VLANs to avoid broadcast propagation (commonly done on the
distribution switch).
• Use VLAN Trunking Protocol (VTP) Transparent mode, because there is little need for a
common VLAN database in hierarchical networks.
• Disable trunking on host ports, because it is not necessary. Doing so provides more security and
speeds up PortFast.
• Consider implementing routing in the access layer to provide fast convergence and Layer 3 load
balancing.
• Use the switchport host commands on server and end-user ports to enable PortFast and disable
channeling on these ports.
• Use Cisco STP Toolkit, which provides
• PortFast: Bypass listening-learning phase for access ports
• Loop Guard: Prevents alternate or root port from becoming designated in absence of bridge
protocol data units (BPDU)
• Root Guard: Prevents external switches from becoming root
• BPDU Guard: Disables PortFast-enabled port if a BPDU is received
Cisco Press CCDA 640-864 Official Certification Guide Fourth Edition, Chapter 3, Page 85