Cisco Updated 300-420 Exam Questions and Answers by cory

The RPF check is performed against the RP address when the PIM router has shared-tree state. In PIM sparse mode, multicast traffic initially flows through the rendezvous point using the shared tree, represented as (*,G) state. For shared-tree traffic, the router verifies that packets arrive from the direction of the RP, because the RP is the root of the shared distribution tree. When the router has source-tree state, represented as (S,G), the RPF check is performed against the multicast source address instead. Dense mode behavior and directly connected membership are not the determining conditions in this question. The key distinction is whether forwarding state is shared-tree or source-tree. Cisco multicast design relies on this behavior to keep PIM forwarding loop free as traffic transitions from shared-tree delivery to shortest-path tree delivery where applicable. Selecting the shared-tree state option correctly identifies when the RP address is used for the RPF calculation. Reference topics: PIM sparse mode, shared tree, source tree, RPF toward RP, (*,G) and (S,G) state.

Human Resources: 10.1.1.112/29; Facilities: 10.1.1.64/27; Engineering: 10.1.1.0/26; Finance: 10.1.1.96/28.

The addressing plan must use VLSM and assign the smallest subnet that satisfies each department’s host requirement without overlapping inside the single /24 block. Engineering needs 32 hosts, so a /27 is not enough because it provides only 30 usable addresses. The smallest listed subnet that satisfies Engineering is 10.1.1.0/26, which provides 62 usable addresses. Facilities needs 18 hosts, so a /27 is appropriate; 10.1.1.64/27 provides 30 usable addresses. Finance needs 12 hosts, so a /28 is sufficient because it provides 14 usable addresses; the matching listed subnet is 10.1.1.96/28. Human Resources needs 5 hosts, so a /29 is sufficient because it provides 6 usable addresses; the matching listed subnet is 10.1.1.112/29. The unused options either overlap with selected ranges, provide too few hosts for the department, or waste address space unnecessarily. Cisco addressing design favors hierarchical, nonoverlapping, right-sized prefixes so the plan remains scalable and easy to summarize where possible.

Gateway Load Balancing Protocol is the first-hop redundancy protocol that provides load balancing while presenting a single default gateway IP address to hosts. Cisco’s GLBP documentation states that GLBP “provides load balancing over multiple routers using a single virtual IP address and multiple virtual MAC addresses.” That wording directly matches the requirement in the question. In a GLBP group, the active virtual gateway answers ARP requests for the virtual IP address and can return different virtual MAC addresses associated with active virtual forwarders. As a result, multiple routers forward traffic for the same subnet rather than leaving one router idle during normal operation. HSRP and VRRP provide first-hop redundancy, but their basic operation uses one active or master forwarding device for a virtual IP at a time unless multiple groups are manually engineered per VLAN. IRDP is not the Cisco campus FHRP used for this design. Therefore, when the requirement is automatic load balancing across multiple routers using one virtual IP and multiple virtual MAC addresses, GLBP is the correct protocol.

The selected IPv6 summary must be the smallest prefix that covers all of the site subnets in the exhibit while not including unnecessary additional networks. IPv6 route summarization works by identifying the common high-order bits shared by the component prefixes and advertising the shortest aggregate that contains them all. Cisco routing design uses summarization at WAN or aggregation boundaries to reduce routing-table size, contain convergence events, and simplify policy. Option C is retained because it represents the aggregate identified by the exhibit answer set. Option A is a different /60 boundary and would be correct only if all component subnets fell under that exact nibble range. Option B is not a usable summary route in normal IPv6 prefix notation as written. Option D is too broad or malformed for a precise site summary. The professional design rule is to summarize on valid nibble or bit boundaries and verify that every component prefix is included without accidentally absorbing unrelated site networks. Reference topics: IPv6 summarization, prefix aggregation, route boundary calculation, WAN route scale, convergence containment.