Subject: route flap monitor web page

From: Dave Thaler <[email-masked]>
Date: Fri, 3 Oct 1997 17:43:49 -0400 (EDT)

http://sydney.eecs.umich.edu/flappers.txt 
gives a list of the top 100 flapping routes as seen from U. Michigan.  
This page is automatically updated every 10 minutes.  The route flap 
monitor has been running since about a week ago (so the # changes are 
since then).

The output looks like the report I posted to the list last week:

 CycleTime Route              #Chgs MeanUpTime MeanDnTime Elapsed
    217.65 204.200.244/24      1730     156.43      61.22     111
    218.76 204.162.119.0/28    1572     157.78      60.98     111
    218.77 204.161.60.32/27    1650     157.31      61.46     111
...

where all times are in seconds.  Routes are ranked by "CycleTime"
which is the mean time to toggle between reachable, unreachable,
and reachable again (or vice versa).

CycleTime, MeanUpTime, and MeanDnTime are all moving averages,
where each observation counts for 20% of the average.
 (new average = 0.8 * old average + 0.2 * observation)
   
"# Chgs" is the number of changes since the flap monitor started up.

Elapsed is the number of seconds since the last change in reachability
status.

-Dave

---

From: Bill Fenner <[email-masked]>
Date: Fri, 3 Oct 1997 16:19:07 PDT

There is a lot of routing instability in the MBone that you can miss if
all you look at is reachability.  The fact that IOS does not trigger
routing updates means that counting to infinity is almost guaranteed to
happen whenever a route goes away, so you may never see short-lived
instability that doesn't finish counting to infinity before the
unstable route comes back.

Two Cisco bugs and one Bay Networks bug which are responsible for a
large percentage of the instability in the MBone are described at
http://ganef.cs.ucla.edu/~masseyd/Route/bugs.html .  Further information
on DVMRP route flapping is at http://ganef.cs.ucla.edu/~masseyd/Route/ .
The most unstable routes (those which change metric more than 60 times
in one hour) are in the "Frequent Flappers Club".

We plan to post a weekly list of the 90th percentile unstable routes;
hopefully eventually we will get the bug-induced noise down to the
point where instability in DVMRP is due to link or router problems and
not implementation bugs.

  Bill