hsrp config

[Network Pro]

Hi,

i have a confusion regaridng hsrp. is the config below correct?

Core 1

interface Vlan 100

ip address 10.10.10.2
no ip redirects
no ip unreachables
no ip proxy-arp
ip flow ingress
ip route-cache policy

standby 1 priority 100 (default)
standby 1 ip 10.10.10.1

standby 1 preempt

Core 2  ---- primary

interface Vlan 100

ip address 10.10.10.3
no ip redirects
no ip unreachables
no ip proxy-arp
ip flow ingress
ip route-cache policy
standby 1 ip 10.10.10.1

standby 1 priority 105
standby 1 preempt

I read on cisco website the priority being 110 (Active) and 100 (standby) - i thought it should be 105 and 100 as the decrement value is 10 - am i correct ?

Thanks

[Sandeep Choudhary]

Hi ,

Here is the sample config for HSRP:

CORE1

interface Vlan10

ip address 10.10.10.1 255.255.255.0

standby 1 ip 10.10.10.10

standby 1 priority 150

standby 1 preempt

standby 2 ip 10.10.10.20

standby 2 preempt

end

CORE2

interface Vlan10

ip address 10.10.10.2 255.255.255.0

standby 1 ip 10.10.10.10

standby 1 preempt

standby 2 ip 10.10.10.20

standby 2 priority 150

standby 2 preempt

end

u can check the status by

CORE1#sh stand

CORE2#sh stand

follow this link ....u will find the solution:

http://journey2ccie.blogspot.de/2010/05/hsrp-on-svi-vlan-interface.html

Regards

Please rate if it helps.

[turnera]

I believe you are tracking correctly.

http://www.cisco.com/en/US/tech/tk648/tk362/technologies_tech_note09186a0080094e8c.shtml

The above link covers a scenario similar to yours. I think that the bottom line is to ensure you have a value that will ensure the standby takes over as a primary HSRP link once the primary has detected a link failure.

[Network Pro]

hi

thanks for youre replies...i am not tracking..i know preempt is not needed if you are not tracking but just got it in case.

i am confused by the priority values...(should the active be 105 or 110 or 120 if the standby priority is 100) - without tracking command does it decrement automatically ?

[Sandeep Choudhary · Accepted solution]

HI ,

yes you are right .

It should be 105.

http://en.wikipedia.org/wiki/Hot_Standby_Router_Protocol

Regards

Please rate if it helps.

[Network Pro]

ok i think i figured out the answer.

If we use the tracking command then we need decrement value (Default 10). so if active is 105 and standby is default (100) then if we use traccking command with a default decrement of 10 then active will go to 95 (105-10) thus the standby will be 100 which is higher than 95 so this will be active

but if we dont use tracking then i think we can use 105 or 110 or 120 or more for active router and standby as 100 or less because in this case we are not tracking so no decrement value...the standby will take over only if active router fails or crashes or if the hsrp address is not pingable then no matter what the value is the standby is, it will take over because the primary has failed.

is my thoery right ?

[Sandeep Choudhary]

You are right,

Assigning priority helps select the active and standby routers. If preemption is enabled, the router with the highest priority becomes the designated active router. If priorities are equal, the primary IP addresses are compared, and the higher IP address has priority.

http://www.ciscozine.com/2008/11/01/how-to-optimize-hsrp/

he HSRP prefers the router with higher priority and, if it is equal, it prefers the highter IP address.

so even if you will not mention the proirity in backyp swicth , it will work perfectly.

Configure tracking, authentication, and timers on the primary router using the following commands:

- standby group_number track interface_name [cost]

- When HSRP tracks an interface, it tells the HSRP process to decrement 10 from the priority if the interface goes down. This command can force the HSRP group to switch its primary and secondary routers based on whether an interface is active. The default cost is 10 and can be modified.

- standby group_number authentication character_string

This command establishes authentication messages to be included in the HSRP multicast. This ensures that only authorized routers can become part of the HSRP group. The string must match all routers in the HSRP group.

Regards

[turnera]

Preemption enables the HSRP router with the highest priority to immediately become the active router.

Priority is determined first by the configured priority value, and then by the IP address. In case of ties,

the primary IP addresses are compared, and the higher IP address has priority. In each case, a higher

value is of greater priority. If you do not use the standby preempt interface configuration command in

the configuration for a router, that router will not become the active router, even if its priority is higher

than all other routers.

A standby router with equal priority but a higher IP address will not preempt the active router.

When a router first comes up, it does not have a complete routing table. You can set a preemption delay

that allows preemption to be delayed for a configurable time period. This delay period allows the router

to populate its routing table before becoming the active router.

If preemption is not enabled, then a router may appear to preempt the active router if it does not receive

any Hello messages from the active router.

Using 110 or 105 will work. However using 105 will ensure that when the deduction of '10' takes place, the new value will be 95, this will ensure that the standby configuration will be a higher(lower) priority value and take over as the primary link.

[Network Pro]

yes but without using hte tracking command does hsrp automatcially decrement by 10? i dont htink this will be the case because hsrp decrements by 10 or whatever value configured only when tracking command is used, isnt it ?

so with out tracking command i think it does not matter what value you use 110 or 120 because the standby will be active only if the primary (ex-active) crashes or if the link fails

let me know if i am wrong ?

[turnera · Accepted solution]

That is correct, without tracking configured, the standby will become the active link upon an active link failure regardless of the values.

[Network Pro]

thanks :)

[Sandeep Choudhary]

Dont forget to rate this post and marked the question as answered.