Route to 203.146.224.0/21 Flapping?

Unanswered Question
Mar 19th, 2007

May i know if in our area, you experience the same? I have it suppressed on my router due to dampening, unfortunately it's the route used to our Thailand office.

I have this problem too.
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sundar.palaniappan Mon, 03/19/2007 - 20:20

Here's the status from looking glass.

The route has been stable for over 3 weeks. Check for problems on your end.

route-server>show ip route 203.146.224.0

Routing entry for 203.146.224.0/21, supernet

Known via "bgp 65000", distance 20, metric 0

Tag 7018, type external

Last update from 12.123.1.236 3w4d ago

Routing Descriptor Blocks:

* 12.123.1.236, from 12.123.1.236, 3w4d ago

Route metric is 0, traffic share count is 1

AS Hops 3

Route tag 7018

HTH

Sundar

nojpt Mon, 03/19/2007 - 20:37

Hello Sundar,

May i know which router server you used? Would it be possible that at your side of the world it may not flap, while it is flapping on my side?

Thanks!

sundar.palaniappan Mon, 03/19/2007 - 20:50

It was ATT.

Though what you are saying is possible but I doubt that may be the case. If that was the case then the provider you are peering with may have already dampened that prefix. Here's a list of looking glass sites that you may want to take a look.

http://www.nanog.org/lookingglass.html

HTH

Sundar

nojpt Tue, 03/20/2007 - 23:52

I was thinking more like, the frequent advertisement and withdrawal came from my ISP that caused the suppression. I looked into my router's damped routes, i have something like 30 thousand lines of prefixes. Is this normal?

mheusinger Wed, 03/21/2007 - 05:56

Hi,

just a side note: route flap dampening is officially NOT recommended any more. There are more problems than gain. Have a look f.e. at RIPE document 378 explaining this recommendation:

http://ripe.net/ripe/docs/ripe-378.html

Excerpt:

4.0 Recommendation

This Routing Working Group document proposes that with the current implementations of BGP flap damping, the application of flap damping in ISP networks is NOT recommended. The recommendations given in ripe-229 and previous documents [2] are considered obsolete henceforth.

If flap damping is implemented, the ISP operating that network will cause side-effects to their customers and the Internet users of their customers' content and services as described in the previous sections. These side-effects would quite likely be worse than the impact caused by simply not running flap damping at all.

So I would turn it off immediately, to avoid connectivity issues. If you have concerns about BGP CPU usage, you could use a route-map to exclude certain networks from dampening. Example configs can also be found online following the links in the above mentioned document.

Hope this helps! Please use the rating system.

Regards, Martin

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