Date: Mon, 02 Sep 2019 04:41:35 +0900 (JST) From: Hiroki Sato <hrs@allbsd.org> To: vas@mpeks.tomsk.su Cc: freebsd-net@freebsd.org Subject: Re: Several IPv6 routers and default gateway choice Message-ID: <20190902.044135.1812305046881448068.hrs@allbsd.org> In-Reply-To: <20190901141047.GA56954@admin.sibptus.ru> References: <20190830021228.GA66465@admin.sibptus.ru> <20190830.121543.1108900942284640156.hrs@allbsd.org> <20190901141047.GA56954@admin.sibptus.ru>
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----Security_Multipart(Mon_Sep__2_04_41_35_2019_771)-- Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Victor Sudakov <vas@mpeks.tomsk.su> wrote in <20190901141047.GA56954@admin.sibptus.ru>: va> Hiroki Sato wrote: va> > Another way to realize failover is to use a common anycast address on va> > multiple routers. For example, a router is always able to have va> > fe80::/64 as an anycast address like this: va> > va> > router# ifconfig igb0 inet6 fe80::/64 anycast va> > va> > and you can simply configure fe80::/64 as the default router on the va> > hosts. Multiple routers with the same fe80::/64 can coexist on the va> > same segment, and hosts will choose one of them with no further va> > configuration. A caveat in this case is that the first router always va> > wins and there is no knob to set the preferences across the routers va> > with the same anycast address configured. va> va> Thank you Hiroki, this was very informative and useful. va> va> Can any IPv6 unicast or link-local address be configured as an anycast va> address of a router? Yes. There is no restriction about address scope. You might want to read RFC 4291, which defines Subnet-Router anycast address, and RFC 2526, which defines the other reserved IPv6 subnet anycast addresses. In general, the former one can be used for routing purpose. va> address of a router? Is this a replacement for VRRP and carp(4)? Mostly yes. VRRP and CARP use a virtual IP address and active heartbeat packets to detect unreachability between the member NICs. They support fine-grained configurations such as heartbeat interval, password, and preference. On the other hand, anycast IPv6 default router uses built-in unreachability detection of the IPv6 core protocol. No control communication happens between NICs with the same anycast address. The client will pick up one router and use it as long as it is reachable. It is only for IPv6, of course. So the anycast address just works if you do not need password or control of the master selection. For master selection, router advertisements with different preference values can be used in combination with anycast addresses. -- Hiroki ----Security_Multipart(Mon_Sep__2_04_41_35_2019_771)-- Content-Type: application/pgp-signature Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- iMcEABMKAC0WIQRsDSNTJ8+Ax5Ae/dLbsH3Gbx9zfwUCXWwe7w8caHJzQGFsbGJz ZC5vcmcACgkQ27B9xm8fc3/MNwIHQWKy2HY3AqQ6I3GyCLW/RwR60OoGYCdQz7ed eEehPjESKFB7gv/Jbk7HkXA3empwu819Yx7pH6VDLAYPza9KVw8CBRYidmjr231e 4x/E1TUVFkO5TcBWM222xyvawDS1EqtBNUeMnGecxvzoT37mHU8mUBZ8lRkMKnOk NUZqPTbLTM6r =VqQN -----END PGP SIGNATURE----- ----Security_Multipart(Mon_Sep__2_04_41_35_2019_771)----
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