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New Member

Rip command

router rip

flash-update-threshold 10 .

Please what is the effect of the above command on the periodic routing update.

5 REPLIES

Re: Rip command

From:

http://www.cisco.com/en/US/docs/ios/iproute/command/reference/irp_rip.html#wp1011167

flash-update-threshold

To suppress regularly scheduled flash updates, use the flash-update-threshold command in router configuration mode. To return to the default state, use the no form of this command.

flash-update-threshold seconds

no flash-update-threshold

Syntax Description

seconds

The time interval in seconds for which the suppression of flash updates can be configured. The range is from 1 to 30 seconds.

Defaults

This command is disabled by default.

Command Modes

Router configuration

Command History

Release Modification

12.0

This command was introduced.

12.2(33)SRA

This command was integrated into Cisco IOS Release 12.2(33)SRA.

12.2SX

This command is supported in the Cisco IOS Release 12.2SX train. Support in a specific 12.2SX release of this train depends on your feature set, platform, and platform hardware.

Usage Guidelines

This command suppresses flash updates when the arrival of a regularly scheduled update matches the number of seconds that is configured with the seconds argument. The range of seconds that can be configure is from 0 to 30 seconds. If the number of seconds matches the number of seconds or is less than the number seconds that is configured with the seconds argument, the flash update is suppressed. If the numbers seconds until the flash update arrives exceeds the number of seconds that is configured with the seconds argument, the flash update is not suppressed. The regular scheduled interval for flash updates and the configuration of the suppression of flash updates can be verified with the show ip protocol command.

Examples

The following example configures a router to suppress a regularly scheduled flash update if the update is due in 10 seconds or less:

router rip

flash-update-threshold 10

Related Commands

Command Description

show ip protocols

Displays the parameters and current state of the active routing protocol process.

New Member

Re: Rip command

This is just a lift from doc cd. I have seen it , and didnt understand...that why I posted the question....please give brief explanation.

Super Bronze

Re: Rip command

RIP router updates (assuming your not using the triggered option) reoccur on a scheduled time interval (Cisco default - every 30 seconds). In addition to these reoccuring updates, RIP can send an immediate update when there's a route change, a "flash" update. This command provides the option to suppress the "flash" update if it's within so many seconds of the regular scheduled update.

The example if the reference doc shows the flash update being suppressed if it occurs within 10 seconds of the schedule. So, if the next scheduled update occurs 33 seconds after the minute, suppress (do not send the flash update) if the clock is between 23 and 33 seconds after the minute, but send the flash update if the clock is between 3 and 23 seconds after the minute.

You might wonder why you would want to delay a route update. Well, often for reasons why Cisco RIP timers default to 30 seconds, i.e. (from same doc [under timers]: "Note By setting a short update period, you run the risk of congesting slow-speed serial lines. A short update period can be a concern on faster-speed Ethernets and T1-rate serial lines. Also, if you have many routes in your updates, you can cause the routers to spend an excessive amount of time processing updates. "

Re: Rip command

I wouldnt say I lifted anything, hence why I copied the web page URL for your additional reference.

Bronze

Re: Rip command

RIP sends routing update based on 2 conditions:

1) Regular 30 second interval (by default)

2) When there is a change to the topology

So if we use 0 as our start time, in a stable network, RIP will send out a copy of its routing table every 30 seconds, so one at 30 seconds, one at 60 seconds etc.

Now if there is a change in the network topology at 27 seconds, RIP will send its full routing table, and then again at the 30 second interval, so in 3 seconds 2 of the exact same messages were sent, if you have a large routing table, you can see how this can waste bandwidth especially on slower links.

So to compensate you can set the flash-update-timer.

In your example you provided it sets the timer to 10 seconds, so if a routing change occurs within 10 seconds of the normal update interval (every 30 seconds) it will prevent the router from sending that update out, and will just include the new change in it's regular interval.

So if a change occurs at 19 seconds, then it will send its routing table, and then again at 30 seconds it will send its regular update interval.

If a change occurs at 20 seconds, it will suppress that update, and just send the update with the regular 30 second interval.

This can help on low bandwidth inks, but can impact network convergence time (time it takes for all devices to be aware of a change). You can see how multiple flash-update-timers in a network with several routers can save a lot of bandwidth, but can also cascade the delay in updates.

If R1 had a topology change at 20 seconds, there would be a 10 second delay to R2, then if R2 also had a flash update timer configured, it could take up to another 10 seconds (for a total of 20 seconds) to update R3.

HTH,

Craig

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