Answers: HSRP 1
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
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1 2 |
interface GigabitEthernet0/1 standby 10 ip 192.168.100.1 |
Example 4: R2 Config
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1 2 |
interface GigabitEthernet0/1 standby 10 ip 192.168.100.1 |
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.
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)
Hi Karm,
Short answer – yep, you were right.
I changed the lab post to reverse those R1/R2 IP addresses, so that the explanation here in this post is now correct. Thanks for the note!
Wendell
Well, here: http://blog.certskills.com/ccna/cl514/,
you tell us to make R2 act as “primary”(active ?).
By “primary” you mean “active” ? If that’s the case R2 wins as stated, right?
Hi,
Yep, I meant “active”. I changed the lab post to use the more correct “active” instead of “primary”. thanks!
Wendell
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…
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
Hi Wendel
I think you didn’t get Victor’s point here or I misunderstood your answer.
In the CML File, tje preconfigured IP Adresses of PC1 is 192.168.100.1 an PC2 192.168.100.2.
So we can’t use 192.168.100.1 as HSRP virtual IP because the ip is already in use by PC1.
Markus
Markus,
Ahh, I get it now. Marked that change in the same task, should also be fixed next week.
Thanks again.
wendell
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,
Hi,
I agree! It’s due to the default setting for no preemption.
Wendell
As mentioned by another student, the config for R2 is missing ‘standby 10 preempt’ in the config to make sure it always becomes active.