Answers: HSRP 1

Wendell
By Wendell December 23, 2015 09:05

This #HSRP lab requires just a few lines of configuration, using defaults for pretty much every option. Check here for the original lab, and check your answers in this post below the fold.

Figure 1: HSRP Design, One LAN Switch

 

Figure 2: HSRP Design, Two LAN Switches

 

Answers

 

Example 3: R1 Config

Example 4: R2 Config

 

Commentary

Hot Standby Router Protocol (HSRP) is a Cisco proprietary First Hop Redundancy Protocol (FHRP) that enables hosts to have redundant gateways. This is important because many LANs are configured with a single gateway that is used by all devices; if this single gateway were to fail, then all of the devices are left without access to external networks (not on the local LAN).

With HSRP, multiple routers reference a single IP address to be used as the default gateway. One router actively provides the data plane function of receiving packets from hosts, while the other waits to take over if the first router fails.

In this example, both R1 and R2 would be configured with a HSRP virtual IP address of 192.168.100.1. Note that the instructions said to use the lowest available IP address; R1 and R2 use two high values in the subnet, so with no other information available, it appears that 192.168.100.1 is available. Both routers must use the same HSRP group number in order to cooperate to create the same HSRP group, so both routers use the command standby 10 ip 192.168.100.1.

Note that HSRP routers choose the router with the highest interface address as the HSRP active router, unless one router is configured with a higher HSRP priority than than the other router. In this case, with neither router configured with an standby priority interface subcommand, both routers use a default priority of 100, therefore relying on the tiebreaker. The tiebreaker is to pick the router with the highest interface IP address; R2 wins in this case, meeting the requirement that R2 be the active router under normal conditions. This means that all of the traffic coming from PC1 will go through R2 unless there is a failure. Note that if you configured on R2 a command like standby 10 priority 101 (or any value greater than 100), I would count it as correct.

OSPF Interface Config 2
HSRP 1
Wendell
By Wendell December 23, 2015 09:05
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9 Comments

  1. Kram December 20, 10:37

    Your answer states “The tiebreaker is to pick the router with the highest interface IP address; R2 wins in this case”

    But according to the config the IP addresses are:
    R1 192.168.100.254
    R2 192.168.100.253

    So wouldn’t R1 win? (254>253)

    Reply to this comment
  2. Viktor February 10, 03:06

    Hi. In the answer you assign 192.168.100.1 for the VIP as the smallest IP in the subnet, but in Host device info from the question we see that 192.168.100.1 and 192.168.100.2 have already been assigned to P1 and PC2. So, following the logic from the task, I suppose the VIP should be 192.168.100.3…

    Reply to this comment
    • certskills February 13, 07:42

      Hi Viktor,
      You are correct. I meant for the lab statement to show .254 and .253 as the last octet of the interface addresses. (Actually, the VIRL file showed those; just didn’t make it into the wordpress post.) Anyway, I changed the lab post to use .254 and .253, so the .1 as VIP here in the answer is now good to use. Thanks for the heads up.
      Regards,
      Wendell

      Reply to this comment
  3. ccentpil May 26, 03:11

    Hello,
    if R1 is still active when R2 is powered on, which router will be the active router ? If I understand the book, in Chapter 20, step 3, A., R1 will be the active router.

    Thanks,

    Reply to this comment
  4. Gabriel Moran November 13, 21:24

    As mentioned by another student, the config for R2 is missing ‘standby 10 preempt’ in the config to make sure it always becomes active.

    Reply to this comment
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