AS7170 flaps and resulting non-event

John Todd jtodd at
Thu Dec 2 16:15:13 UTC 1999

Thanks for the info!  I'll drop them a line.

I'm actually not worried about their route flaps per se; I'm more 
interested in why it's not been noticed by anyone else who actually 
peers with them.  I received another message that may explain that: 
at least one private peer with 7170 has reported no such flapping.

My not-so-easy-to-see point was "If this fairly large AS is flapping 
so hard, and it's flapping to all it's peers, and nobody is noticing, 
does this indicate a fundamental change in what is permissible or at 
least tolerated?  Is this tolerance due to fatter, faster routers or 
simply aggressive dampening?"

I think the answer is "Not enough data to go on from this example." 
because part of that line of "if"s above was not met (7170 is 
apparently not flapping all it's sessions; perhaps this is just a 
Merit-specific problem.)


>AT&T-DISC is an AT&T Network that is specifically for DREN/DISC DoD 
>Government use.
>It is not their public/commercial IP service offering.
>What is DREN:
>What is DISC:
>For a while now I understand this network is working with a skeleton 
>operations crew and none of the original architects have been there 
>for a long time. And some of the Merit folks that were under 
>contract to AT&T DISC as advisors also have left Merit recently.
>It is probally best to take up any issues you have with the DISC 
>HELP DESK information available at:
>They are located either in Vienna, VA off Gallows Rd (right near 
>MAE-EAST) or Oakton VA (Down Rt 123 - again near MAE-EAST).
>and/or also take up the issue with the Technical Advisory Panel at 
>the same time:
>And I see that this list is out of date.
>hope this helps you getting your concern resolved.
>23:22 -0800 12/01/1999, John Todd wrote:
>>Starting on the 19th of this month, the Merit routing report shows 
>>that AT&T-DISC(AS7170) is having some serious flapping issues with 
>>the Merit route server at the MAE-East (ten million updates in a 
>>day, as an example.)  Among other things, I'm interested if these 
>>flaps are being made to all peers of AS7170 at the MAE-East.  If 
>>that is the case, then nobody has noticed, or nobody cares, or 
>>nobody has raised it in a public forum yet.  If the silence has 
>>been caused by one of the first two situations, I'm interested in 
>>which is the true reason that there has been no hue and cry over 
>>this abnormal number of route insertions/removals.
>>A few questions and items to chew on:
>> 1: Is this something that anyone other than Merit is noticing? 
>>Could it be that AS7170 just doesn't have that many peers, or that 
>>the routes are flapping only to Merit's route server?
>> 2: Is this just being dampened to the point where nobody notices?
>> 3: Is the silence on this issue somehow indicative of the 
>>increased speed/memory of core routers in the North American and 
>>other routing structures?  [main point] If so, then this changes 
>>some arguments about who and why one will/will not peer, as well as 
>>dragging the corpse of "Sprint filtering" out of the grave.[/main 
>> 4: Am I just reading this data incorrectly?  I don't have a direct 
>>peer with 7170 anywhere, so I can't look at my own records for 
>>Side notes:
>> A: This isn't AT&T's only AS number - they have two others (7018 
>>and 5075) that seem to be used for quite a few announcements.  In 
>>fact, 7170 may not be the "primary" AS for AT&T - again, I don't 
>>have a crystal ball to see how they structure their announcements 
>>across the multiple AS'es.
>> B: It's not easily possible for me to find which routes were 
>>flapping; could this be just a few routes out of the N that 7170 
>>announces?  (See 
>>ast.7170.view.991128 for an exhaustive list of 7170's routes to 
>>Merit on the 28th)  If it's only a few of the routes, then perhaps 
>>dampening by peers simply quashed the rogue networks into oblivion 
>>without anyone noticing that these few routes were missing.
>> C: Could this be related? 
>>  I 
>>don't think so, but it's an interesting note nonetheless.  I don't 
>>see how DNS could be attached to the route flaps, but again I don't 
>>have a crystal ball into AT&T's network.
>>I've included selected sections from Merit's daily route flap mail. 
>>To see a complete list of the messages, browse to 
>> for more 
>>Largest Sources of BGP Instability
>>(announcements + withdraws = total)
>>Dec 01: 1.  AT&T-DISC (AS7170) at Mae-East 10432535 + 36800 = 
>>10469335 BGP prefix updates
>>Nov 30: 1.  AT&T-DISC (AS7170) at Mae-East 10432535 + 36800 = 
>>10469335 BGP prefix updates
>>Nov 29: 1.  AT&T-DISC (AS7170) at Mae-East 11122216 + 16465 = 
>>11138681 BGP prefix updates
>>Nov 28: 1.  AT&T-DISC (AS7170) at Mae-East 10256555 + 17732 = 
>>10274287 BGP prefix updates
>>Nov 27: 1.  AT&T-DISC (AS7170) at Mae-East 9882016 + 23527 = 
>>9905543 BGP prefix updates
>>. [similar results in here]
>>Nov 19: 1.  AT&T-DISC (AS7170) at Mae-East 2462647 + 93171 = 
>>2555818 BGP prefix updates
>>[AT&T-DISC does not show up in the mail from the 18th or 17th, 
>>leading me to think these flaps started during the measured 
>>interval reported on the 19th.]
>>jtodd at

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