Good question, RFC2526 hs more meat concerning anycast reserver addresses, I have a couple questions too;
1) Can you allocate additional anycast addresses out of the unicast space other than the 127-n bits identified? 2) how does your client machine behave when a reservered anycast address is used? On Thu, Sep 2, 2010 at 7:53 AM, Philipp Geschke <[email protected]>wrote: > Hello, > > I seem to have issues understanding IPv6 anycast on NI MLX/XMR. > My understanding is, that any router that does have an IPv6 address in a > subnet should be listening on the Subnet-Router anycast address (RFC3513 > section 2.6.1). > > When I configure an IPv6 unicast address on a MLX VE it shows that it > joins the Subnet-Router anycast address (2001:db8:f1:c:: [Anycast]): > > Interface VE 200 is up, line protocol is up > [...] > IPv6 is enabled, link-local address is fe80::20c:dbff:fee1:2f00 > [Preferred] > Global unicast address(es): > 2001:db8:f1:c::2 [Preferred], subnet is 2001:db8:f1:c::/64 > 2001:db8:f1:c:: [Anycast], subnet is 2001:db8:f1:c::/64 > 2001:db8:f1:c::1 [Anycast], subnet is 2001:db8:f1:c::/64 > 2001:db8:f1:c:: [Anycast], subnet is 2001:db8:f1:c::/64 > Joined group address(es): > ff02::1:ff00:1 > ff02::1:ff00:0 > ff02::1:ff00:2 > ff02::1:ffe1:2f00 > ff02::2 > ff02::1 > [...] > > Now when I try to ping that address from a client within the network > 2001:db8:f1:c::/64, I get a neighbour advertisement from the MLX announcing > it's UNIcast address: > > 16:02:40.548719 IP6 (hlim 255, next-header ICMPv6 (58) payload length: 32) > 2001:db8:f1:c::160 > ff02::1:ff00:0: [icmp6 sum ok] ICMP6, neighbor > solicitation, length 32, who has 2001:db8:f1:c:: > source link-address option (1), length 8 (1): 00:16:3e:19:16:a9 > 0x0000: 0016 3e19 16a9 > 16:02:40.548719 IP6 (class 0xc0, hlim 255, next-header ICMPv6 (58) payload > length: 32) 2001:db8:f1:c::2 > 2001:db8:f1:c::160: [icmp6 sum ok] ICMP6, > neighbor advertisement, length 32, tgt is 2001:db8:f1:c::2, Flags [router, > solicited] > destination link-address option (2), length 8 (1): > 00:0c:db:e1:2f:00 > 0x0000: 000c dbe1 2f00 > > This causes the asking client to create an entry in its neighbour cache > for the routers unicast address, but not realising, that this was the > answer to its question, hence it keeps on sending solicitation messages for > the anycast address. > In my understanding the neighbour advertisement should have the unicast > address as source, but should announce the anycast address. > > If I take a Linux box and enable ip6 forwarding in the kernel, it also > joins that very same anycast group. If I do the same test again, you can > see, > that the Linux box answers with its unicast address, announcing the > anycast address: > > 12:50:36.194948 IP6 (hlim 255, next-header ICMPv6 (58) payload length: 32) > 2001:db8:f1:c::160 > 2001:db8:f1:c::21: [icmp6 sum ok] ICMP6, neighbor > advertisement, length 32, tgt is 2001:db8:f1:c::, Flags [router, solicited] > destination link-address option (2), length 8 (1): > 00:16:3e:19:16:a9 > 0x0000: 0016 3e19 16a9 > > This works and the client creates an entry in its neighbour cache for the > anycast address and can now communicate with the address. > > Same goes for the explicitly configured anycast address 2001:db8:f1:c::1 > you can see in the output of the interface. > > If it matters, I do have ipv6 nd suppress-ra active on that VE. > > > So what does this mean, is it > > a) Me not understanding the concept of the anycast address (basicaly I > want to use it as a default gateway)? > b) A problem with my configuration (which is pretty plain for v6 right > now)? > c) A bug? > d) ?? > > Does anyone have experience with that they are able to share? > > > Thanks for any hints, > Philipp > > _______________________________________________ > foundry-nsp mailing list > [email protected] > http://puck.nether.net/mailman/listinfo/foundry-nsp >
_______________________________________________ foundry-nsp mailing list [email protected] http://puck.nether.net/mailman/listinfo/foundry-nsp
