Re: [dhcwg] DHCPv6 Failover -- LAST CHANCE

perl-list <> Thu, 08 September 2016 13:25 UTC

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Date: Thu, 08 Sep 2016 09:09:19 -0400
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Thread-Topic: DHCPv6 Failover -- LAST CHANCE
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Cc: dhcwg <>, Kim Kinnear <>
Subject: Re: [dhcwg] DHCPv6 Failover -- LAST CHANCE
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> From: "tianxiang li" <>
> To: "Kim Kinnear" <>
> Cc: "dhcwg" <>
> Sent: Wednesday, September 7, 2016 10:37:06 PM
> Subject: Re: [dhcwg] DHCPv6 Failover -- LAST CHANCE
> 4.2.1 Independent allocation

> “In this allocation scheme, used for allocating individual IPv6 addresses,
> available IPv6 addresses are permanently (until server configuration changes)
> split between servers…”

> If active-passive mode is used, it would mean that the addresses in the
> secondary server would not be used unless the primary server fails. In that
> case, wouldn’t permanently splitting the addresses between the primary and
> secondary server a waste of addresses?

> If the address pool in the primary server becomes scarce, wouldn’t a rebalancing
> mechanism be useful?

I read this section as just a codifying of what we do now without failover. We put half the /64 on the "primary" and half on the "secondary". It provides for some enhanced behavior where clients won't need to get a new address in the case of server failure as the remaining server can renew addresses. Also, you wouldn't need to do any math as the server would arithmetically split in half for you any subnets that are marked for this behavior. If offered a choice in the future, I would probably choose this method as it is the simplest. 

Also, this bit here: "It also assumes that the pool assigned to each server will never deplete." negates your comment about addresses becoming scarce. It is highly recommended (by all articles and documentation that I've seen) that all end networks be configured as /64 subnets. There are quite a lot of addresses in a /64. More than are in the entire IPv4 address space, is my understanding. It is unlikely that a /64 will experience IP address scarcity.