RE: VRRP - Multiple Masters Question

Here are the comments I put in my implementation. The summary is
that I slow down my timer if I hear from a higher priority system
with a slower interval. All other cases (I claim) aren't an issue.
This is the last step in packet validation:

 /* MUST verify that the Adver Interval in the packet is the same as
 ** the locally configured for this virtual router */
 /* OK, that's what the spec says, but actually it makes very
  * little sense: all it does is insure the two routers with
  * different times argue over the MAC address, etc., while
  * ignoring each other's packets. Notice that this would
  * happen while the time was being reconfigured on multiple
  * systems. So I ignore that requirement, and instead take his
  * timer value if it's larger than mine and he has higher
  * priority. (If I have higher priority, I continue using my
  * own time: I shouldn't have heard from him, anyway.) note
  * that we're checking against our configured interval, not
  * this entry's interval: this entry could have been
  * previously slowed down, only to be speeded up again
  * (possibly already the way to our configured interval, hence
  * the greater than *or equal to*).
  */
 vrrp_interval = VRRP_TIME_TO_MS( vrrp->adver_int );
 if ( ( vrrp_interval != entry->adver_int )
      && ( vrrp_interval >= vrrpd_adver_int )
      && ( vrrp->priority > entry->priority ) )
 { /* he's better than me, so just use his advertisement
    * interval, automatically changing the down interval.
    * (if he's running faster than us, it's not an issue,
    * which is good because we don't want to change our
    * scheduling rate. if he ever gets set to a lower
    * value, we'll see it and adjust again, possibly
    * making it back down to our own value (although
    * we'll never explicitly notice that.)
    */
   entry->adver_int = vrrp_interval;
 }

-don

> -----Original Message-----
> From: [email protected] [mailto:[email protected]]On Behalf Of
> Radia Perlman
> Sent: Friday, December 02, 2005 1:05 PM
> To: Hott, Robert W CIV B35-Branch
> Cc: Chappell, Brett L CIV B35-Branch; Odonoghue,Karen F CIV 
> B35-Branch;
> Plunkett,Timothy R CIV B35-Branch; [email protected]
> Subject: Re: [VRRP] VRRP - Multiple Masters Question
> 
> 
> I agree with you that protocols should be resilient to configuration 
> differences between nodes,
> and I think the ideal solution is what you suggested (use the 
> timer as 
> advertised by the master)
> rather than what's in the spec (discard messages that 
> disagree with your 
> setting, so that
> multiple masters will be elected, ignoring each others' messages). 
> Especially in conjunction with
> bridges, multiple masters are dangerous.
> 
> This was brought up on the mailing list before I was watching this 
> group, and somehow
> the discussion fizzled out. I think the subsecond timer draft 
> is a good 
> excuse to revisit this,
> and make sure, if the WG really wants to keep the behavior as it is, 
> that it is doing it
> consciously.
> 
> So please, people, speak up about which behavior you prefer:
> 
> a) discard (and log an error) if the value advertised in the VRRP 
> message disagrees with your
> configured value for hello timer....this is what is currently 
> specified
> b) use the interval advertised by the master, for as long as 
> it is master
> 
> If we switch to b), then another decision is whether that is 
> configured 
> misconfiguration or not,
> i.e., if an error should be logged.
> 
> Radia
> 
> 
> 
> 
> 
> Hott, Robert W CIV B35-Branch wrote:
> 
> > I am in the process of updating a draft for sub-second 
> timers for VRRP 
> > for IPv4. An area that I have struggled with has been how 
> to deal with 
> > legacy devices that might be on a network with devices that use 
> > sub-second timers. In thinking out this issue for this new draft, I 
> > noticed something that seems to a problem with the current RFC. The 
> > interesting area in RFC 3768 is section 7.1 on receiving 
> VRRP packets.
> >
> > The issue is this. Suppose that I have a master router 
> configured with 
> > an advertisement interval of 1 second. I have two more routers 
> > configured as backups. One is configured with an advertisement 
> > interval of 2 seconds and another is configured with an 
> advertisement 
> > interval of 3 seconds.
> >
> > I know that this is problematic but it could happen. Anyway, the 
> > master would send an advertisement. Based upon section 7.1, both of 
> > the backups would discard this advertisement and would report the 
> > misconfiguration. Since the advertisement would be discarded, both 
> > would eventually transition to masters. The end result 
> would be three 
> > masters, since the state machine would not act on the advertisement.
> >
> > Did I interpret this correctly? I would think that you 
> would not want 
> > to discard the advertisement because of the wrong setting. I would 
> > think you would want to use the interval of the master, at 
> least until 
> > you assume the role of the master.
> >
> > Bob Hott
> >
> > *Robert (Bob) W. Hott*
> > *NSWC-DD*
> > *Code B35, Bldg. 1500A/122A*
> > *17320 Dahlgren Road*
> > *Dahlgren, VA 22448-5100*
> > *540-653-1497 (W)*
> > *540-653-8673 (FAX)*
> > *[email protected] (E-mail)*
> >
> >-------------------------------------------------------------
> -----------
> >
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> >  
> >
> 
> 
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