Re: Some thoughts about "path failover"

RE: [Mobike] Some thoughts about "path failover"Dear Jing,

See, this is exactly the problem. If YOU want to send path testing packets out simultaneously, that's great, but if (insert the name of a major ISP here) craters and ALL their customers decide to simultaneously test ALL their alternative paths, that's not something I'm looking forward to.

We're really spoiled by overprovisioned network paths. Sometimes we're spoiled enough to forget that when we lose path connectivity, we may not be the only ones affected, and the exact moment when everybody is selecting new paths that are now carrying more traffic, because the new paths still work, is exactly the wrong time to start throwing more traffic into the network.

Synchronization is good in swimming and not good in path failover.

Spencer
  ----- Original Message ----- 
  From: Jing Xiang 
  To: [email protected] ; [email protected] ; [email protected] 
  Sent: Friday, April 23, 2004 9:18 AM
  Subject: RE: [Mobike] Some thoughts about "path failover"




  Spencer/Pasi, 

  I think sending packets over all paths simultaneously or sequentially can be useful 
  depending on circumstances. e.g. some customers might want to recover the connection 
  ASAP at any cost, in this case sending path testing packets out simultaneously might 
  make sense. In other cases, some customer might prefer certain paths because of cost and 
  not care much about recovering speed, then sending path testing packets sequentially 
  (subject to retry interval & retries) might make sense. 
  It should not be that hard to have the protocol accormodate both cases. I don't see 
  any reasons we need to exclude either case in our considerations. 

  Regards! 
  /Jing 

  -----Original Message----- 
  From: [email protected] [mailto:[email protected]]On 
  Behalf Of [email protected] 
  Sent: Wednesday, April 21, 2004 9:55 AM 
  To: [email protected]; [email protected] 
  Subject: RE: [Mobike] Some thoughts about "path failover" 



  Hi Spencer, 

  I think we should consider this somehow. At least we should not 
  send the path testing packets over all paths simultaneously, but 
  instead separated by a short interval (since the paths could 
  share links). 

  My guess is that this is closer to RTO, but then again, window 
  size in IKEv2 is not really related to congestion control (though 
  in some sense, "path failover" is trying to detect if the missing 
  packets were due to congestion, a broken link, or a dead peer). 

  (I created new issue #14 about this so we don't forget this.) 

  Best regards, 
  Pasi 

  > -----Original Message----- 
  > From: [email protected] on behalf Of Spencer Dawkins 
  > Sent: Friday, April 16, 2004 2:20 PM 
  > To: [email protected] 
  > Subject: Re: [Mobike] Some thoughts about "path failover" 
  > 
  > 
  > 
  > > >    - Initiator sends the previous IKEv2 request (not a new one, 
  > > >      to avoid problems with window size) over all the paths. 
  > 
  > I know the Internet has changed a bit since Slow Start was introduced 
  > :-} 
  > 
  > but my impression was that if you think you have a problem, sending 
  > multiple packets into the network is not the right thing to so. You're 
  > talking about sending single packets over multiple paths, but we don't 
  > know how disjoint the paths are (so they may all traverse one link 
  > somewhere on the way). Should we ignore this, or think about it? 
  > 
  > Pasi, do you have a sense that we're talking about a recovery 
  > mechanism that we use during Fast Recovery, or during RTO (to put 
  > things in TCP-speak)? 
  > 
  > Spencer 
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