Well, there were some curious situations in our network and I was trying to test them in my lab. So thats why im trying to put route into hold-down.
Most of what you have said works in practice, but it oposes to 'Jeff Doyle TCP/IPvol1' and 'Caslow, Pavlichenko - Bridges Routers and Switches for CCIE's'.
Doyle says that: "...An update with a hop count higer than the metric recorded in the routing table will cause route to go into hold-down for 180 seconds...". CCO also does not bother to provide more acurate information on that.
I suspect that RIP holddown behavior has changed in more recent releases. I have heard that with IOS 11.x RIP behaves exacactly as Doyle says. Its a pitty that Cisco does not document these things...
When a network is in hold down the network is not accessible. So any time a router receives an update from a different neighbour with a poorer metric about the same route it will be not accessible. That does not make sense.
I am an instructor for the Cisco networking academy program so I had a look through the material to see what is says. Here is what it came up with:
When a router receives an update from a neighbor indicating that a previously accessible network is now inaccessible, the router marks the route as inaccessible and starts a hold-down timer. If at any time before the hold-down timer expires an update is received from the same neighbor indicating that the network is again accessible, the router marks the network as accessible and removes the hold-down timer.
If an update arrives from a different neighboring router with a better metric than originally recorded for the network, the router marks the network as accessible and removes the hold-down timer.
If at any time before the hold-down timer expires an update is received from a different neighboring router with a poorer metric, the update is ignored. Ignoring an update with a poorer metric when a hold-down timer is in effect allows more time for the knowledge of a disruptive change to propagate through the entire network.
hope this helps
to place a bunch of networks into hold down for testing purposes. on the router you want the hold down to occour set the up date timer and hold down timer to two seconds and keep the dead timer the same
Regarding the books the poorer metric must be receved from the current next-hop for route to go to hold-down, so in theory there is no problem with availability (actualy there is less availability than only to react to unreachable metrics).
CNA RIP Curriculum has one thing that does not work in parctice - the route is not put to hold-down if it was advertized by neighbor with unachable metric. It ONLY goes to hold-down if the local invalid timer for the route expired.
If you have some small routers you can check that by yourself. I have tried this with 12.2T, and I heard rumours that older releases might behave more close to theory.
Hi everyone, I would like to thank you in advance for any help you can provide a newcomer like myself!
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