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Hold timer,invalid timer,flush timer,what are the differences between


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#1 Even_Zhang

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Posted 27 November 2008 - 01:52 AM

Take the RIP protocol as example,by default,invalid timer is 180s,hold down timer is 180s,flush timer is 240s.
If a route is down,then the local router notice and begin counting.After 180 seconds passed,the route would be tagged as invalid.Then hold down timer will be started?After next 240 seconds,this route will be flushed(or cleared)?
I am puzzled how long it takes to delete a route.30s(update timer)+150s+180(hold down timer)+60s=420s
Am i right?anyone could help me?
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#2 TESLA.COIL

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Posted 27 November 2008 - 07:50 AM

i had a similar confusion regarding the timers.420sec is 7minutes and its correct,its easier to understand if u divide those 420 seconds into various phases of timers that the routers undergoes.

that invalid timer of 180 seconds is inclusive of those 30 seconds underwhich an update is to be expected.

1)0 - 30 ( normal periodic timer)
2)31-180 secs( total of 150 secs) = 3 minutes( invalid timer,incl.of (1) ) changes the status to possibly down
3)181-359 =6minutes (waiting for an update & status should be possibly down)
4)360-420 = 7minutes (after all those 420 seconds are counted the route is flushed from the routing table)

initially i just added 180+180+240 = 600 secs = 10 mins hehe which is wrong.

Edited by TESLA.COIL, 27 November 2008 - 07:53 AM.

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#3 Even_Zhang

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Posted 27 November 2008 - 10:26 AM

i had a similar confusion regarding the timers.420sec is 7minutes and its correct,its easier to understand if u divide those 420 seconds into various phases of timers that the routers undergoes.

that invalid timer of 180 seconds is inclusive of those 30 seconds underwhich an update is to be expected.

1)0 - 30 ( normal periodic timer)
2)31-180 secs( total of 150 secs) = 3 minutes( invalid timer,incl.of (1) ) changes the status to possibly down
3)181-359 =6minutes (waiting for an update & status should be possibly down)
4)360-420 = 7minutes (after all those 420 seconds are counted the route is flushed from the routing table)

initially i just added 180+180+240 = 600 secs = 10 mins hehe which is wrong.


Could we see the status using "debug" command?
However,when I use GNS sofware,I can't find any information about that.
Do you have a good idea to monitor these status?
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#4 weak ale

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Posted 27 November 2008 - 10:29 AM

It's actually 4 min until a route is flushed. 30 sec is the regular update interval. If after 180 secs there is no update, the route is poisoned. If after a total of 240 secs nothing changes, the route is flushed from the cache. Hold down is a separate timer that says that the router won't accept any new advertisement for a poisoned route until that timer has elapsed.
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#5 TESLA.COIL

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Posted 27 November 2008 - 10:44 AM

i used the packet tracer and it was 7 minutes time it took the delete the route. you can see by usng the command show ip route and show ip protocols ,for the amt of time it takes.

Edited by TESLA.COIL, 27 November 2008 - 10:48 AM.

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#6 weak ale

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Posted 27 November 2008 - 03:44 PM

All I can say is that's strange and doesn't match my experience at all. You might try it again - setup two routers connected via ethernet and setup a few loopbacks on one router, then setup rip for those networks. Run "debug ip rip" on the router w/o loopbacks, and then shutdown the ethernet on the router with loopbacks. watch the debugs and occasionally run "show ip route" on the router w/o loopbacks. I'm guessing the routes to your loopbacks are marked inaccessible around 3 to 3.5 min and disappear somewhere around the 4 min mark.
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