Subject: flappers

From: Dave Thaler <[email-masked]>
Date: Sat, 27 Sep 1997 15:09:45 -0400 (EDT)

I've been looking at some route flapping again today...

The top two sites with flapping routes (as seen from U. Michigan) at the 
moment are:

Iowa State University (AS93, AS6122)

 CycleTime Route           #changes  MeanUpTime  MeanDownTm  Elapsed
    573.37 205.221.187/24        38     479.47      93.90     472
    573.42 205.221.190/23        38     479.27      94.15     472
    573.73 205.221.192/22        38     489.58      84.15     472
    638.04 205.221.150/24        36     513.24     121.05     532
    638.04 205.221.151/24        36     505.18     127.50     532
    641.11 205.221.174/24        38     519.93     118.77     532
    ...

Data Research Associates Inc. (AS1746)

 CycleTime Route           #changes  MeanUpTime  MeanDownTm  Elapsed
    587.27 206.187.176/24        37     500.01      87.26      44
    587.27 206.187.178/24        37     500.01      87.26      44
    587.27 206.187.179/24        37     500.01      87.26      44
    587.27 206.187.180/24        37     515.63      71.64      44
    616.15 206.187.169/24        35     530.27      85.88      44
    ...

Times are in seconds, so routes with a cycle time of < 600 are flapping
more often than every 10 minutes.

Both of these sites are injecting a large number of /24's (most of
which aren't included above) with the same metric.  Can these be 
aggregated into a single /16 (which is what both sites own according 
to Internic)?  Since both seem to always have some routes reachable,
the aggregate should be stable.

It looks like both of them get service through MCI.

-Dave

---

From: Bill Fenner <[email-masked]>
Date: Mon, 29 Sep 1997 09:16:57 PDT

>The top two sites with flapping routes (as seen from U. Michigan) at the 

Our experience in doing detailed analysis during the summer has been
that the top flappers are either victims of the Cisco "blaster" bug, or
of the Bay Networks overlapping route bug.  A Cisco unicast/DVMRP
distance configuration error is a distant third.  Aggregation certainly
does help reduce the instability, since it means there will be one
unstable route instead of hundreds, but from our data, huge
instabilities are due to bugs and not to unstable networks.

I'm in favor of aggregating, but I doubt that it will solve the
instability problem for either site.

We're planning to post a weekly list of the top N flapping routes, in
the hopes that it will encourage the owners of the flapping networks to
find out why their networks are flapping and perhaps even fix it.

  Bill

---

From: Dave Thaler <[email-masked]>
Date: Mon, 29 Sep 1997 12:20:24 -0400 (EDT)

Bill wrote:
> distance configuration error is a distant third.

Someone from Iowa State U. indicated to me in email (or at least this
is how I interpreted their email...) that their routes weren't supposed 
to be advertised into the MBone in the first place, so there's at
least a fourth problem.

-Dave

---

From: "Jeffrey C. Ollie" <[email-masked]>
Date: Mon, 29 Sep 1997 20:25:08 -0500

-----BEGIN PGP SIGNED MESSAGE-----

Bill Fenner <[email-masked]> wrote:
>
> the Bay Networks overlapping route bug.

I am curious, as we run Bay Networks routers here, if you can tell me
which versions of the Bay router code suffer from this bug and if it
has been fixed what version was it fixed in?  I hope to get our mbone
connection going again and I want to make sure that I don't cause
problems for others.  FYI, the routers that have DVMRP enabled here
are running version 11.02/2.

[A copy of the headers and the PGP signature follow.]

Cc: [email-masked]
Date: Mon, 29 Sep 1997 20:25:08 -0500
From: "Jeffrey C. Ollie" <[email-masked]>
In-Reply-To: <[email-masked]>
References: <[email-masked]>
	<[email-masked]>
Subject: Re: flappers
To: Bill Fenner <[email-masked]>

-- 
Jeffrey C. Ollie                     |            Should Work Now (TM)

---

From: Bill Fenner <[email-masked]>
Date: Mon, 29 Sep 1997 18:48:25 PDT

"Jeffrey C. Ollie" <[email-masked]> wrote:
>has been fixed what version was it fixed in?

I have no idea.  Bay is unable to replicate the bug so they closed the
bug report.

  Bill