Solved: hello time and hold time in hsrp

sarahr202 · ‎01-18-2009

hi every body!

My cisco press book says hold time in hsrp is 3 times the hello time.

I am just wondering if it is possible to set hold time as 50 seconds while keeping the hello time 3 seconds.

thanks a lot!

Edison Ortiz · ‎01-18-2009

Hi Sarah :)

You can change the hello and hold timers value with the standby timers command: http://www.cisco.com/en/US/docs/ios/ha/command/reference/ha_s3.html#wp1044847

However, a hold time that high can create convergence issues in your configuration.

A router will wait that long before considering a neighbor unreachable.

HTH,

__

Edison.

View solution in original post

Joseph W. Doherty · ‎01-18-2009

You could, but the reason for hold time being 3x hello time, it assumes 3 lost hellos really indicates a lost neighbor, not just a lost hello packet or two. Holding for 50 seconds would mean there were about 16 missed hellos which really probably doesn't increase the accuracy of the neighbor being down but certainly increases the wait before the HSRP shifts the IP address. If a 50 second hold time was acceptable, you could set the hello time to 16 seconds which would decrease the workload for processing HSRP. (Today, we're usually more interested in even faster reaction to failure, which is why millisecond HSRP [ver. 2] and BFD are supported on newer equipment.)

View solution in original post

crow930us · ‎01-18-2009

Ask yourself what kind of traffic is going across your network. If you are using VOIP, how much of an affect would it be if your network was down for 50 seconds, or even 10 seconds.

You need to think about what will be happening to your packets while your Active device is down and there is nothing else routing packets (black hole). Network Admins set up HSRP to provide a first-hop redundancy within a network.

If anything you would want to lower the hello timer down to 1 second and the hold timer to 4 seconds for faster failover.

View solution in original post

Edison Ortiz · ‎01-20-2009

Here we can see "Next hello sent in 00:00:00.480"

By the way what does 480 indicates?

00.480 indicates milliseconds.

Here we can see the active router does not overwrite the timer on standby-router which contradicts the statement from the link.

Am i correct?

Something is wrong with your setup there. I see the Hot Standby value different on both routers.

Anyway, here is my test:

R2#sh stand

FastEthernet0/0 - Group 0

State is Active

2 state changes, last state change 00:04:08

Virtual IP address is 192.168.12.254

Active virtual MAC address is 0000.0c07.ac00

Local virtual MAC address is 0000.0c07.ac00 (v1 default)

Hello time 3 sec, hold time 10 sec

Next hello sent in 1.592 secs

Preemption enabled

Active router is local

Standby router is 192.168.12.1, priority 100 (expires in 9.396 sec)

Priority 200 (configured 200)

IP redundancy name is "hsrp-Fa0/0-0" (default)

R1#sh stand

FastEthernet0/0 - Group 0

State is Standby

1 state change, last state change 00:03:56

Virtual IP address is 192.168.12.254

Active virtual MAC address is 0000.0c07.ac00

Local virtual MAC address is 0000.0c07.ac00 (v1 default)

Hello time 3 sec, hold time 10 sec

Next hello sent in 1.848 secs

Preemption enabled

Active router is 192.168.12.2, priority 200 (expires in 8.072 sec)

Standby router is local

Priority 100 (default 100)

IP redundancy name is "hsrp-Fa0/0-0" (default)

R2#conf t

Enter configuration commands, one per line. End with CNTL/Z.

R2(config)#int f0/0

R2(config-if)#standby timers 20 60

R2(config-if)#do show stand

FastEthernet0/0 - Group 0

State is Active

2 state changes, last state change 00:04:49

Virtual IP address is 192.168.12.254

Active virtual MAC address is 0000.0c07.ac00

Local virtual MAC address is 0000.0c07.ac00 (v1 default)

Hello time 20 sec, hold time 60 sec

Next hello sent in 19.040 secs

Preemption enabled

Active router is local

Standby router is 192.168.12.1, priority 100 (expires in 59.848 sec)

Priority 200 (configured 200)

IP redundancy name is "hsrp-Fa0/0-0" (default)

!

R1#show stand

FastEthernet0/0 - Group 0

State is Standby

1 state change, last state change 00:04:39

Virtual IP address is 192.168.12.254

Active virtual MAC address is 0000.0c07.ac00

Local virtual MAC address is 0000.0c07.ac00 (v1 default)

Hello time 20 sec, hold time 60 sec

Next hello sent in 2.168 secs

Preemption enabled

Active router is 192.168.12.2, priority 200 (expires in 41.380 sec)

Standby router is local

Priority 100 (default 100)

IP redundancy name is "hsrp-Fa0/0-0" (default)

R1#show run int f0/0

Building configuration...

Current configuration : 178 bytes

!

interface FastEthernet0/0

description R2

ip address 192.168.12.1 255.255.255.0

duplex auto

speed auto

standby ip 192.168.12.254

standby preempt

no clns route-cache

end

!

You can see no standby timers command on R1, yet it's using the Active HSRP timersâ€¦

HTH,

__

Edison.

View solution in original post

Edison Ortiz · ‎01-21-2009

It will use 3 and 10 - timers from the active router. I did a packet trace and confirmed this behavior.

The configured entry indicates the configuration is different than the current active HSRP router but this value could be the prevailing value if this router was to ever become an active HSRP router.

HTH,

__

Edison.

View solution in original post

Edison Ortiz · ‎01-18-2009

Hi Sarah :)

You can change the hello and hold timers value with the standby timers command: http://www.cisco.com/en/US/docs/ios/ha/command/reference/ha_s3.html#wp1044847

However, a hold time that high can create convergence issues in your configuration.

A router will wait that long before considering a neighbor unreachable.

HTH,

__

Edison.

sarahr202 · ‎01-19-2009

Hi Edison !

Let me quote from the link, you forwarded:

"The timers configured on the active router always override any other timer settings"

I performed a simple lab on two routers( 2500 that is all I can afford now:-), D4 and C3 both are connected via layer 2 switch. D4 is active while C3 is stand-by.

I changed the timers, hello time and hold time to 20 and 60 seconds respectively.

C3##show standby

Ethernet0 - Group 1

Local state is Standby, priority 100

Hellotime 3 holdtime 10 configured hellotime 20 sec holdtime 60 sec

Next hello sent in 00:00:00.480

Hot standby IP address is 150.150.150.150 configured

Active router is 196.196.196.4 expires in 00:00:08

Standby router is local

Here we can see "Next hello sent in 00:00:00.480"

By the way what does 480 indicates?

-------------------------------

The active router has default settings.

D4#show standby

Ethernet0 - Group 1

Local state is Active, priority 200, may preempt

Hellotime 3 holdtime 10

Next hello sent in 00:00:01

Hot standby IP address is 196.196.196.6 configured

Active router is local

Standby router is 196.196.196.3 expires in 00:00:07

--------------------------------------------------

Here we can see the active router does not overwrite the timer on standby-router which contradicts the statement from the link.

Am i correct?

thanks a lot!

Edison Ortiz · ‎01-20-2009

Here we can see "Next hello sent in 00:00:00.480"

By the way what does 480 indicates?

00.480 indicates milliseconds.

Here we can see the active router does not overwrite the timer on standby-router which contradicts the statement from the link.

Am i correct?

Something is wrong with your setup there. I see the Hot Standby value different on both routers.

Anyway, here is my test:

R2#sh stand

FastEthernet0/0 - Group 0

State is Active

2 state changes, last state change 00:04:08

Virtual IP address is 192.168.12.254

Active virtual MAC address is 0000.0c07.ac00

Local virtual MAC address is 0000.0c07.ac00 (v1 default)

Hello time 3 sec, hold time 10 sec

Next hello sent in 1.592 secs

Preemption enabled

Active router is local

Standby router is 192.168.12.1, priority 100 (expires in 9.396 sec)

Priority 200 (configured 200)

IP redundancy name is "hsrp-Fa0/0-0" (default)

R1#sh stand

FastEthernet0/0 - Group 0

State is Standby

1 state change, last state change 00:03:56

Virtual IP address is 192.168.12.254

Active virtual MAC address is 0000.0c07.ac00

Local virtual MAC address is 0000.0c07.ac00 (v1 default)

Hello time 3 sec, hold time 10 sec

Next hello sent in 1.848 secs

Preemption enabled

Active router is 192.168.12.2, priority 200 (expires in 8.072 sec)

Standby router is local

Priority 100 (default 100)

IP redundancy name is "hsrp-Fa0/0-0" (default)

R2#conf t

Enter configuration commands, one per line. End with CNTL/Z.

R2(config)#int f0/0

R2(config-if)#standby timers 20 60

R2(config-if)#do show stand

FastEthernet0/0 - Group 0

State is Active

2 state changes, last state change 00:04:49

Virtual IP address is 192.168.12.254

Active virtual MAC address is 0000.0c07.ac00

Local virtual MAC address is 0000.0c07.ac00 (v1 default)

Hello time 20 sec, hold time 60 sec

Next hello sent in 19.040 secs

Preemption enabled

Active router is local

Standby router is 192.168.12.1, priority 100 (expires in 59.848 sec)

Priority 200 (configured 200)

IP redundancy name is "hsrp-Fa0/0-0" (default)

!

R1#show stand

FastEthernet0/0 - Group 0

State is Standby

1 state change, last state change 00:04:39

Virtual IP address is 192.168.12.254

Active virtual MAC address is 0000.0c07.ac00

Local virtual MAC address is 0000.0c07.ac00 (v1 default)

Hello time 20 sec, hold time 60 sec

Next hello sent in 2.168 secs

Preemption enabled

Active router is 192.168.12.2, priority 200 (expires in 41.380 sec)

Standby router is local

Priority 100 (default 100)

IP redundancy name is "hsrp-Fa0/0-0" (default)

R1#show run int f0/0

Building configuration...

Current configuration : 178 bytes

!

interface FastEthernet0/0

description R2

ip address 192.168.12.1 255.255.255.0

duplex auto

speed auto

standby ip 192.168.12.254

standby preempt

no clns route-cache

end

!

You can see no standby timers command on R1, yet it's using the Active HSRP timersâ€¦

HTH,

__

Edison.

sarahr202 · ‎01-20-2009

Thanks a lot Edison!

sarahr202 · ‎01-21-2009

Hi Edison !

Sorry for being stubborn.

I came up with different scenario.

In your case, you changed the timer on active router. In mine i changed the timer on standby router.

D4e0-------------------sw------------e0C3

where D4 is active while C3 is standby

Here I changed the timer on C3( standby router)

C3(config)#int e0

C3(config-if)#standby 1 timer 20 60

C3(config-if)#end

show standby on C3

show standby

Ethernet0 - Group 1

Local state is Standby, priority 100

Hellotime 3 holdtime 10 configured hellotime 20 sec holdtime 60 sec

Next hello sent in 00:00:02.488

Hot standby IP address is 196.196.196.15 configured

Active router is 196.196.196.4 expires in 00:00:09

"configured hellotime 20 sec holdtime 60 sec" ,

Which timers c3 is using, the ones i configured 20 and 60 0r 3 and 10( from the active router)

Thanks a lot!

Edison Ortiz · ‎01-21-2009

It will use 3 and 10 - timers from the active router. I did a packet trace and confirmed this behavior.

The configured entry indicates the configuration is different than the current active HSRP router but this value could be the prevailing value if this router was to ever become an active HSRP router.

HTH,

__

Edison.

Joseph W. Doherty · ‎01-18-2009

You could, but the reason for hold time being 3x hello time, it assumes 3 lost hellos really indicates a lost neighbor, not just a lost hello packet or two. Holding for 50 seconds would mean there were about 16 missed hellos which really probably doesn't increase the accuracy of the neighbor being down but certainly increases the wait before the HSRP shifts the IP address. If a 50 second hold time was acceptable, you could set the hello time to 16 seconds which would decrease the workload for processing HSRP. (Today, we're usually more interested in even faster reaction to failure, which is why millisecond HSRP [ver. 2] and BFD are supported on newer equipment.)

crow930us · ‎01-18-2009

Ask yourself what kind of traffic is going across your network. If you are using VOIP, how much of an affect would it be if your network was down for 50 seconds, or even 10 seconds.

You need to think about what will be happening to your packets while your Active device is down and there is nothing else routing packets (black hole). Network Admins set up HSRP to provide a first-hop redundancy within a network.

If anything you would want to lower the hello timer down to 1 second and the hold timer to 4 seconds for faster failover.