Date: Thu, 12 Sep 2019 12:32:49 +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: <20190912.123249.93293774363511628.hrs@allbsd.org> In-Reply-To: <20190906035608.GA45741@admin.sibptus.ru> References: <20190901141047.GA56954@admin.sibptus.ru> <20190902.044135.1812305046881448068.hrs@allbsd.org> <20190906035608.GA45741@admin.sibptus.ru>
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----Security_Multipart(Thu_Sep_12_12_32_49_2019_424)-- Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Victor Sudakov <vas@mpeks.tomsk.su> wrote in <20190906035608.GA45741@admin.sibptus.ru>: va> Hiroki Sato wrote: va> > va> Can any IPv6 unicast or link-local address be configured as an anycast va> > va> address of a router? va> > va> > Yes. There is no restriction about address scope. va> > va> > You might want to read RFC 4291, which defines Subnet-Router anycast va> > address, and RFC 2526, which defines the other reserved IPv6 subnet va> > anycast addresses. In general, the former one can be used for va> > routing purpose. va> va> Interestingly, RFC4291 says that "All routers are required to support va> the Subnet-Router anycast addresses for the subnets to which they have va> interfaces." In practice, I don't observe this. A FreeBSD router does va> not configure such an address automatically, for example. They will be automatically configured when an ipv6_prefix_IF rc.conf(5) variable is used to configure a prefix: ----(from rc.conf(5) man page)---- ipv6_prefix_ed0="2001:db8:1:0 2001:db8:2:0" is equivalent to the following: ifconfig_ed0_alias0="inet6 2001:db8:1:: eui64 prefixlen 64" ifconfig_ed0_alias1="inet6 2001:db8:1:: prefixlen 64 anycast" ifconfig_ed0_alias2="inet6 2001:db8:2:: eui64 prefixlen 64" ifconfig_ed0_alias3="inet6 2001:db8:2:: prefixlen 64 anycast" These Subnet-Router anycast addresses will be added only when ipv6_gateway_enable is YES. ---------------------------------- va> RFC2526 is dim, I think it's because of this RFC the last usable address va> on a subnet ends in ff7f instead of ffff. I wonder if anyone anywhere va> uses those subnet anycast addresses. That is because there are few practical applications of the IPv6 anycast address other than failover across multiple routers. -- Hiroki ----Security_Multipart(Thu_Sep_12_12_32_49_2019_424)-- Content-Type: application/pgp-signature Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- iMgEABMKAC0WIQRsDSNTJ8+Ax5Ae/dLbsH3Gbx9zfwUCXXm8YQ8caHJzQGFsbGJz ZC5vcmcACgkQ27B9xm8fc38S/gIJAcwUb3Ryw6kARieLYhNOMv5BH0VsyVVuXNHu xqnZvUX2OuzHOdXEWPSKSifKarzg/dzbaQJQfvb6Tv6tfnF+382TAgiChka4ljSk BAWxqFtRSOQCTLi1MaJ/5U5XNnTAH/+uRLpZfcXofojot20SCkOeIF4tFGxJ+hb9 Aafc4L7UMWBOcw== =9znI -----END PGP SIGNATURE----- ----Security_Multipart(Thu_Sep_12_12_32_49_2019_424)----
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