An MC Question with STP, 802.1Q, ARP, and MAC tables
Today’s post is a question that comes with the ICND2 Official Cert Guide. A reader had sent in an errata email, claiming the question was wrong (it wasn’t in this case), but this question is packed with tons of learning points. I thought it’d be a good one to review here in the blog. I’ll post the question today, and work through a couple of the answers in the coming posts.
The figure shows a LAN with three switches, a router using 802.1Q trunking, and VLANs 11 and 13. Subnet 10.1.1.0/24 is on VLAN 11, and subnet 10.1.3.0/24 is on VLAN 13. The STP topology has converged for each VLAN, with SW1 blocking on fa0/2 for VLAN 11, and SW2 blocking on fa0/3 for VLAN 13. Assume that the PCs and router have complete and full information in their ARP tables, and that all three switches have current and valid MAC address table entries for the MAC addresses of the PCs and the router. Under those conditions, which of the following statements best describes the MAC address tables used in each VLAN?
a) SW2’s MAC table for VLAN 13 lists R1’s MAC with interface F0/11
b) SW2’s MAC table for VLAN 13 lists PC3’s MAC with interface F0/3
c) A frame that R1 forwards to PC1 passes over the trunk from SW2 to SW1
d) A frame that R1 forwards to PC3 passes over the trunk from SW2 to SW1
e) When PC2 pings PC3, the ICMP Echo Request passes through SW1