Subject: RE: [dhcwg] Failover: transition out of potential-conflict.

From: "Bernie Volz (EUD)" <[email-masked]>
Date: Mon, 5 Nov 2001 13:30:45 -0600

I'm a bit confused as to what the problem really is. When both servers contact
each other, the primary will request the secondary to send it full details. Once
the primary has done that, why can it not lease out addresses? It has all of the
information in order to do this.

In your message Ted, you state:

"Since the network partition has healed, the primary can hear requests
from all networks, and one of the first leases it assigns happens to be
the same free lease that the secondary reclaimed and assigned.   This
creates a needless conflict.   The conflict will be caught during the
secondary's update, but this is cold comfort, since we potentially have
an address conflict at this point."

The primary doesn't leave Potential-Conflict until it has received ALL BNDUPDs
from the secondary. And, it can't do any leasing in the Potential-Conflict state.
So, how possibly can the primary assign "the same free lease that the secondary
reclaimed and assigned"? Since the secondary sent that BNDUPD to the primary
before the primary entered NORMAL, why would the primary give that
address to any other client?

- Bernie

-----Original Message-----
From: Ted Lemon [mailto:[email-masked]]
Sent: Monday, November 05, 2001 1:59 PM
To: Kim Kinnear
Cc: [email-masked]
Subject: Re: [dhcwg] Failover: transition out of potential-conflict.

>
>         But, I think the primary would not actually assign the IP
>         address to anyone after it goes into NORMAL state.  Part
>         of the work of the primary processing the secondary's
>         lease database is for the primary to resolve conflicts in
>         real time while receiving the BNDUPD's.  The secondary
>         cannot send the UPDDONE until the primary has processed
>         all of the BNDUPD's in some way.

I misspoke slightly there - I said "NORMAL" when I meant "CONFLICT-DONE."   
The primary will think that the address is in the free state until it gets 
the update from the secondary telling it that the secondary assigned it to 
a client.   So there's a window, potentially fairly long at a large 
installation, in which the primary can allocate that address, thinking it 
is free.   If it does so, the problem will be discovered during the 
resolution process, but it'll be too late at that point - two clients will 
have been assigned the same IP address.

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---

From: Ted Lemon <[email-masked]>
Date: Mon, 5 Nov 2001 13:13:46 -0700

> information in order to do this.

D'oh!   My brain appears to have been operating on only one cylinder.   You 
are quite correct.   I'm sorry for the confusion that I may have caused by 
bringing this up.