"standby delay" command introduced in HSRP

tc-nakajima · ‎06-08-2008

Hi all,

Is "standby delay" command introduced in HSRP often used in production network(WAN edge, Campus lan, etc..)?

I don't have much knowledge about the production network so please help me with this.

Delaying the Initialization of HSRP on an Interface

http://www.cisco.com/en/US/docs/ios/ipapp/configuration/guide/ipapp_hsrp_ps6350_TSD_Products_Configuration_Guide_Chapter.html#wp1054843

Thank you,

Taichi

Pravin Phadte · ‎06-09-2008

Most IP hosts have an IP address of a single router configured as the default gateway. When HSRP is used, the HSRP virtual IP address is configured as the host's default gateway instead of the IP address of the router.

HSRP is useful for hosts that do not support a router discovery protocol (such as ICMP Router Discovery Protocol [IRDP]) and cannot switch to a new router when their selected router reloads or loses power. Because existing TCP sessions can survive the failover, this protocol also provides a more transparent recovery for hosts that dynamically choose a next hop for routing IP traffic. HSRP is useful for hosts that do not support a router discovery protocol (such as ICMP Router Discovery Protocol [IRDP]) and cannot switch to a new router when their selected router reloads or loses power. Because existing TCP sessions can survive the failover, this protocol also provides a more transparent recovery for hosts that dynamically choose a next hop for routing IP traffic.

When HSRP is configured on a network segment, it provides a virtual MAC address and an IP address that is shared among a group of routers running HSRP. The address of this HSRP group is referred to as the virtual IP address . One of these devices is selected by the protocol to be the active router. The active router receives and routes packets destined for the MAC address of the group. When HSRP is configured on a network segment, it provides a virtual MAC address and an IP address that is shared among a group of routers running HSRP. The address of this HSRP group is referred to as the virtual IP address. One of these devices is selected by the protocol to be the active router. The active router receives and routes packets destined for the MAC address of the group.

HSRP detects when the designated active router fails, at which point a selected standby router assumes control of the MAC and IP addresses of the Hot Standby group. A new standby router is also selected at that time.HSRP detects when the designated active router fails, at which point a selected standby router assumes control of the MAC and IP addresses of the Hot Standby group. A new standby router is also selected at that time.

Standby delay is a useful command when network convergence is needed in the network. This command need to be used when you are running HSRP. Mostly when you need a router or a switch to act as a primary and not a secondary device you need to have this command. For link flaps some time in eigrp or may be a possibility in lan and most of the time it happens in WAN where the link keeps on flapping. HSRP config without any standby delay would create a problem in this kind of network design.

Hope this helps.

foxbatreco · ‎06-09-2008

The standby delay command is used for delaying the pre-empting ability of the active router(with high priority),if it goes down/the interface goes down for somereason.

Say the current active router goes down/gets rebooted.By default config & if preempt is enabled, this will again regain the role of active router once it reloads conmpletely, with no delays. Typically default value is 0 seconds.

command syntax is :

standby 1 preempt delay

The delay option can be configured with values from 0 to 3600 seconds.But normally its kept to default values.

If its manually configured with a different value , say 180 seconds, this will indicate the reloading once active router ( with high priority) to wait for a time frame of 180 seconds before it again preempts existing router and attains the active state for communication with the end clients.

Enabling this with manual value depends on production criticality. If u want the environment to continue functioning with the current router only and not have a slight transition disconnection once the original active router reloads, u can specify this.

But anyhow the delay can be only max 1 hour.

Also, the state change again wont create a noticeable disconnection, if the delay is kept to default.

Pls rate if this helps!!!

tc-nakajima · ‎06-10-2008

Thanx for the comments!

I confirmed "standby delay..." is valid when interface flapped.

Tested using "standby delay minimum 10 reload 120" with "debug standby" and

flapped(shut/no shut) the interface manually.

Below message appeared when shut the interface and waited for few seconds.

*Jun 6 19:27:39.084: HSRP: Fa0/1 API Software interface coming up

*Jun 6 19:27:39.084: HSRP: Fa0/1 API Add active HSRP addresses to ARP tableshu

R2(config-if)#shutdown

*Jun 6 19:27:45.896: HSRP: Fa0/1 Interface up

*Jun 6 19:27:45.896: HSRP: Fa0/1 Starting minimum interface delay (10 secs) <<<<<<<<<<<<<<<<<<

Below message appeared when no shut the interface and waited for few seconds.

*Jun 6 19:27:50.122: HSRP: Fa0/1 API Software interface going down

*Jun 6 19:27:50.122: HSRP: Fa0/1 Interface down

*Jun 6 19:27:50.122: HSRP: Fa0/1 Stopping minimum interface delay <<<<<<<<<<<<<<<<<<

*Jun 6 19:27:50.122: HSRP: Fa0/1 API Software interface going down

*Jun 6 19:27:50.126: HSRP: Fa0/1 API Add active HSRP addresses to ARP table

*Jun 6 19:27:52.126: %LINK-5-CHANGED: Interface FastEthernet0/1, changed state to adminis

tratively down

Below message appeared when timer expired and the active router came back active again.

*Jun 6 19:54:52.590: HSRP: Fa0/1 Interface min delay expired <<<<<<<<<<<<<<<<<<

Also tested with no "standby delay..." command but this time,

shut/no shut made the HSRP state to flap.