This chapter covers the following exam topics:
3.0 IP Connectivity
3.5 Describe the purpose, functions, and concepts of First Hop Redundancy Protocols
Any host’s default router serves as the first router, or first hop, in the routing path from sender to receiver. However, IPv4 did not include high-availability and redundancy features related to the default router. IP hosts use a single setting with a single default router IP address. Also, IP did not define a backup or load-sharing mechanism for multiple routers connected to the same subnet.
First Hop Redundancy Protocols (FHRPs) add the function of redundancy and load sharing for the default router function in any subnet.
This chapter begins with the concepts central to all FHRPs. All FHRPs define how multiple routers work together to appear as a single default router, sharing responsibility. All the FHRPs hide their existence from the hosts, so there is no change to host routing logic. The second section examines the most popular FHRP: Hot Standby Router Protocol (HSRP). The final section compares HSRP with the other two FHRPs: Virtual Router Redundancy Protocol (VRRP) and Global Load Balancing Protocol (GLBP).
“Do I Know This Already?” Quiz
Take the quiz (either here or use the PTP software) if you want to use the score to help you decide how much time to spend on this chapter. The letter answers are listed at the bottom of the page following the quiz. Appendix C, found both at the end of the book as well as on the companion website, includes both the answers and explanations. You can also find both answers and explanations in the PTP testing software.
Table 16-1 “Do I Know This Already?” Foundation Topics Section-to-Question Mapping
Foundation Topics Section |
Questions |
|---|---|
First Hop Redundancy Protocols |
1, 2 |
Hot Standby Router Protocol |
3, 4 |
VRRP and GLBP Concepts |
5, 6 |
1. R1 and R2 attach to the same Ethernet VLAN, with subnet 10.1.19.0/25, with addresses 10.1.19.1 and 10.1.19.2, respectively, configured with the ip address interface subcommand. Host A refers to 10.1.19.1 as its default router, and host B refers to 10.1.19.2 as its default router. The routers do not use an FHRP. Which of the following is a problem for this LAN?
The design breaks IPv4 addressing rules because two routers cannot connect to the same LAN subnet.
If one router fails, neither host can send packets off-subnet.
If one router fails, both hosts will use the one remaining router as a default router.
If one router fails, the host that uses that router as a default router cannot send packets off-subnet.
2. R1 and R2 attach to the same Ethernet VLAN, with subnet 10.1.19.0/25, with addresses 10.1.19.1 and 10.1.19.2, respectively, configured with the ip address interface subcommand. The routers use an FHRP. Host A and host B attach to the same LAN and have correct default router settings per the FHRP configuration. Which of the following statements is true for this LAN?
The design breaks IPv4 addressing rules because two routers cannot connect to the same LAN subnet.
If one router fails, neither host can send packets off-subnet.
If one router fails, both hosts will use the one remaining router as a default router.
If one router fails, only one of the two hosts will still be able to send packets off-subnet.
3. R1 and R2 attach to the same Ethernet VLAN, with subnet 10.1.19.0/25, with addresses 10.1.19.1 and 10.1.19.2, respectively, configured with the ip address interface subcommand. The routers use HSRP. The network engineer prefers to have R1 be the default router when both R1 and R2 are up. Which of the following is the likely default router setting for hosts in this subnet?
10.1.19.1
10.1.19.2
Another IP address in subnet 10.1.19.0/25 other than 10.1.19.1 and 10.1.19.2
A host name that the FHRP mini-DNS will initially point to 10.1.19.1
4. Routers R1, R2, and R3, with addresses 10.1.1.1, 10.1.1.2, and 10.1.1.3, respectively, are in HSRPv2 group 16, and use VIP 10.1.1.8. R2 is the current HSRP active router. Which statement is true about HSRP operation in the subnet?
Traffic from hosts in the subnet balances across all routers (R1, R2, and R3).
Traffic from hosts in the subnet flows into only router R2.
Router R1 only replies to ARP requests for address 10.1.1.8.
The HSRP group uses virtual MAC 0000.0C9F.F016.
5. Routers R1, R2, and R3, with addresses 10.1.1.1, 10.1.1.2, and 10.1.1.3, respectively, are in VRRPv3 group 32. R3 is the current VRRP active router. Which statements are true about VRRP operation in the subnet? (Choose two answers.)
The current VIP may be 10.1.1.3.
The current VIP must be 10.1.1.3.
VRRP sends its group messages to multicast address 224.0.0.18.
VRRP sends its group messages to multicast address 224.0.0.2.
6. Which answer best describes a mechanism that enables GLBP to achieve active/active load balancing, with all routers in the group forwarding packets as a default router?
By configuring a VIP that matches one of the router’s interface IP addresses
By using a different VIP per router in the same group
By using a separate GLBP group for each router
By using a different virtual MAC address per router in the same group
Answers to the “Do I Know This Already?” quiz:
1 D
2 C
3 C
4 B
5 A, C
6 D