netdev - Re: [PATCH] bonding: send IPv6 neighbor advertisement on failover

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Message-ID: <17192.1223490884@death.nxdomain.ibm.com>
Date:	Wed, 08 Oct 2008 11:34:44 -0700
From:	Jay Vosburgh <fubar@...ibm.com>
To:	Vlad Yasevich <vladislav.yasevich@...com>
cc:	Brian Haley <brian.haley@...com>,
	David Miller <davem@...emloft.net>,
	Simon Horman <horms@...ge.net.au>,
	Alex Sidorenko <alexandre.sidorenko@...com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH] bonding: send IPv6 neighbor advertisement on failover

Vlad Yasevich <vladislav.yasevich@...com> wrote:

>> +
>> +	list_for_each_entry(bond, &bond_dev_list, bond_list) {
>> +		if (bond->dev == event_dev) {
>> +			switch (event) {
>> +			case NETDEV_UP:
>> +				ipv6_addr_copy(&bond->master_ipv6, &ifa->addr);
>> +				return NOTIFY_OK;
>
>I think you want to store the first address configured on the device (most
>likely link-local), and not overwrite it every time  a new address is
>configured.  Since new addresses can be configured rather often (think
>temporary, new RAs, etc) we really want the most stable address we can have.
>Also, since ND is a link protocol, link-local is sufficient.

	That depends upon how the IPv6 unsolicited NAs are handled by
the switch.  For IPv4, we issue a gratuitous ARP for one of the IP
addresses on the interface to update the switch's MAC table; for this
case, it doesn't matter which IP address is used.

	If IPv6-smart switches snoop the same way, then it again doesn't
matter which IPv6 address is used; this is just to update the MAC table.
I'll agree that it's logically sensible to use a link-local, though.
If, on the other hand, IPv6 needs an update for each configured address,
then storing just one IPv6 address is insufficient (as we'd need an NA
for each address).

	-J

---
	-Jay Vosburgh, IBM Linux Technology Center, fubar@...ibm.com
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