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Date:	Wed, 29 Oct 2014 15:37:32 +0100
From:	Hannes Frederic Sowa <>
To:	Erik Kline <>
Subject: Re: [PATCH v2 net-next] net: ipv6: Add a sysctl to make optimistic
 addresses useful candidates

On Di, 2014-10-28 at 18:11 +0900, Erik Kline wrote:
> Add a sysctl that causes an interface's optimistic addresses
> to be considered equivalent to other non-deprecated addresses
> for source address selection purposes.  Preferred addresses
> will still take precedence over optimistic addresses, subject
> to other ranking in the source address selection algorithm.
> This is useful where different interfaces are connected to
> different networks from different ISPs (e.g., a cell network
> and a home wifi network).
> The current behaviour complies with RFC 3484/6724, and it
> makes sense if the host has only one interface, or has
> multiple interfaces on the same network (same or cooperating
> administrative domain(s), but not in the multiple distinct
> networks case.
> For example, if a mobile device has an IPv6 address on an LTE
> network and then connects to IPv6-enabled wifi, while the wifi
> IPv6 address is undergoing DAD, IPv6 connections will try use
> the wifi default route with the LTE IPv6 address, and will get
> stuck until they time out.
> Also, because optimistic nodes can receive frames, issue
> an RTM_NEWADDR as soon as DAD starts (with the IFA_F_OPTIMSTIC
> flag appropriately set).  A second RTM_NEWADDR is sent if DAD
> completes (the address flags have changed), otherwise an
> RTM_DELADDR is sent.
> Also: add an entry in ip-sysctl.txt for optimistic_dad.
> Signed-off-by: Erik Kline <>
> ---
> [...]
> +static inline bool ipv6_use_optimistic_addr(struct inet6_dev *idev)
> +{
> +	return idev && idev->cnf.optimistic_dad && idev->cnf.use_optimistic;

Just a small nit: is this idev != NULL check necessary?

Acked-by: Hannes Frederic Sowa <>


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