<div>Good question, RFC2526 hs more meat concerning anycast reserver addresses, I have a couple questions too;</div>
<div> </div>
<div>1) Can you allocate additional anycast addresses out of the unicast space other than the 127-n bits identified? </div>
<div> </div>
<div>2) how does your client machine behave when a reservered anycast address is used?</div>
<div><br><br> </div>
<div class="gmail_quote">On Thu, Sep 2, 2010 at 7:53 AM, Philipp Geschke <span dir="ltr"><<a href="mailto:foundry-nsp@pgmail.net">foundry-nsp@pgmail.net</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid">Hello,<br><br>I seem to have issues understanding IPv6 anycast on NI MLX/XMR.<br>My understanding is, that any router that does have an IPv6 address in a<br>
subnet should be listening on the Subnet-Router anycast address (RFC3513<br>section 2.6.1).<br><br>When I configure an IPv6 unicast address on a MLX VE it shows that it<br>joins the Subnet-Router anycast address (2001:db8:f1:c:: [Anycast]):<br>
<br>Interface VE 200 is up, line protocol is up<br> [...]<br> IPv6 is enabled, link-local address is fe80::20c:dbff:fee1:2f00<br>[Preferred]<br> Global unicast address(es):<br> 2001:db8:f1:c::2 [Preferred], subnet is 2001:db8:f1:c::/64<br>
2001:db8:f1:c:: [Anycast], subnet is 2001:db8:f1:c::/64<br> 2001:db8:f1:c::1 [Anycast], subnet is 2001:db8:f1:c::/64<br> 2001:db8:f1:c:: [Anycast], subnet is 2001:db8:f1:c::/64<br> Joined group address(es):<br> ff02::1:ff00:1<br>
ff02::1:ff00:0<br> ff02::1:ff00:2<br> ff02::1:ffe1:2f00<br> ff02::2<br> ff02::1<br> [...]<br><br>Now when I try to ping that address from a client within the network<br>2001:db8:f1:c::/64, I get a neighbour advertisement from the MLX announcing<br>
it's UNIcast address:<br><br>16:02:40.548719 IP6 (hlim 255, next-header ICMPv6 (58) payload length: 32)<br>2001:db8:f1:c::160 > ff02::1:ff00:0: [icmp6 sum ok] ICMP6, neighbor<br>solicitation, length 32, who has 2001:db8:f1:c::<br>
source link-address option (1), length 8 (1): 00:16:3e:19:16:a9<br> 0x0000: 0016 3e19 16a9<br>16:02:40.548719 IP6 (class 0xc0, hlim 255, next-header ICMPv6 (58) payload<br>length: 32) 2001:db8:f1:c::2 > 2001:db8:f1:c::160: [icmp6 sum ok] ICMP6,<br>
neighbor advertisement, length 32, tgt is 2001:db8:f1:c::2, Flags [router,<br>solicited]<br> destination link-address option (2), length 8 (1):<br>00:0c:db:e1:2f:00<br> 0x0000: 000c dbe1 2f00<br><br>This causes the asking client to create an entry in its neighbour cache<br>
for the routers unicast address, but not realising, that this was the<br>answer to its question, hence it keeps on sending solicitation messages for<br>the anycast address.<br>In my understanding the neighbour advertisement should have the unicast<br>
address as source, but should announce the anycast address.<br><br>If I take a Linux box and enable ip6 forwarding in the kernel, it also<br>joins that very same anycast group. If I do the same test again, you can<br>see,<br>
that the Linux box answers with its unicast address, announcing the<br>anycast address:<br><br>12:50:36.194948 IP6 (hlim 255, next-header ICMPv6 (58) payload length: 32)<br>2001:db8:f1:c::160 > 2001:db8:f1:c::21: [icmp6 sum ok] ICMP6, neighbor<br>
advertisement, length 32, tgt is 2001:db8:f1:c::, Flags [router, solicited]<br> destination link-address option (2), length 8 (1):<br>00:16:3e:19:16:a9<br> 0x0000: 0016 3e19 16a9<br><br>This works and the client creates an entry in its neighbour cache for the<br>
anycast address and can now communicate with the address.<br><br>Same goes for the explicitly configured anycast address 2001:db8:f1:c::1<br>you can see in the output of the interface.<br><br>If it matters, I do have ipv6 nd suppress-ra active on that VE.<br>
<br><br>So what does this mean, is it<br><br>a) Me not understanding the concept of the anycast address (basicaly I<br>want to use it as a default gateway)?<br>b) A problem with my configuration (which is pretty plain for v6 right<br>
now)?<br>c) A bug?<br>d) ??<br><br>Does anyone have experience with that they are able to share?<br><br><br>Thanks for any hints,<br>Philipp<br><br>_______________________________________________<br>foundry-nsp mailing list<br>
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