DHCP failover doesn't receive DHCP requests in secondary server

Gregory Sloop gregs at sloop.net
Thu Aug 16 17:05:20 UTC 2018

But I believe it's always [at least for a long time] been available. IIRC it wasn't recommended to use any split other than even, but it was possible. 
The way it seemed to me was, that there was almost no conceivable situation where it made sense to run it other than an even split. 

...because the only reason I can see to have it run with more leases to one peer vs the other would be if one of the peers couldn't handle all the load, while running even. But then how in the world would one expect the machine that can't even handle half the load to survive when in a peer-down situation where it has to handle ALL the load, and likely more heavy than "normal," since all the non owned leases would get renewed at the MCLT time instead of the full regular lease time.

So I'm probably not thinking of some corner case, but I honestly can't think of a case where a non-even split makes the slightest sense. Thus the option, while nice - doesn't seem to have any real-world practical use.

Sorry to the OP for the digression... :)

I saw it recently in the release notes. 

split bits;

The split statement specifies the split between the primary and secondary for the purposes of load balancing. Whenever a client makes a DHCP request, the DHCP server runs a hash on the client identification, resulting in value from 0 to 255. This is used as an index into a 256 bit field. If the bit at that index is set, the primary is responsible. If the bit at that index is not set, the secondary is responsible. The split value determines how many of the leading bits are set to one. So, in practice, higher split values will cause the primary to serve more clients than the secondary. Lower split values, the converse. Legal values are between 0 and 256 inclusive, of which the most reasonable is 128. Note that a value of 0 makes the secondary responsible for all clients and a value of 256 makes the primary responsible for all 

Source: https://www.isc.org/wp-content/uploads/2018/02/dhcp44.html

On Thu, 16 Aug 2018 at 16:23, Anders Löwinger <anders at abundo.se> wrote:
On 8/15/18 6:19 PM, Philippe Maechler wrote:
> iirc with the latest patch, only the primary server replies to clients 
> when the split value is set to 255

When was this added?


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