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I am implementing IPv6 in my network and for now I have my own routable IPv6 /48 block, Cisco routers, Cisco switches, OSPF between them and several hosts. Its all working fine, but there is something confusing, like:

  1. Most utilities I can use are showing link-local addresses (LL) and I see no fast way to determine which host own it. For example I want to know what router was chosen by host and I use netstat -r6 and see some LL or two. To understand which host it is I have to login onto any possible router to see what link-level address it own. I see possible options to solve this:

    • Host can register LL in DNS. However I think its quite improbable because address assigning is usually not a userland function.

    • There may be a utility which can search through network and say something about LL.

    • I can assign manual LL address for routers which will be more readable.

    • I can make routers to do RAs with unique address instead of LL. Some people says its always LL, but I am not sure (details follow).

  2. Its always said that local routes are done with local address, but it seem to be not always true:

switch#show ipv6 route      
ON2 ::/0 [110/1]
     via 2001:DB8:FFFF:27::E, Vlan27
ON2 2001:DB8:FFFF:20::/64 [110/20]
     via FE80::223:5DFF:FE0A:B95B, Vlan27
C   2001:DB8:FFFF:27::/64 [0/0]
     via Vlan27, directly connected

The one sending default route via OSPF with unique is Cisco ISR G2 router, and the one sending route with LL is Cisco 3750-E switch. The question are:

  • is it OK to have route destination as a unique address? I always thought that destination address is always local because it demand zero effort to determine MAC and send packet since every host have neighbor table with LL<->MAC.
  • am I missing some configuration which can use unique addresses in RAs and OSPF destination or its just different behavior and does not matter?
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    If you are just meaning routers, then I see a lot of people assign fe80::1 to all the Router 1 interfaces, and fe80::2 to all the router 2 interfaces, etc. If you assign Router IDs in the OSPFv3 configuration, then you will see those in the OSPF database. – Ron Maupin♦ May 21 '20 at 18:17
  • Yes, of course I don't care about messy address for any host. Do I understand correctly that your advice is to assign manual link-local address for any router so they always are understandable and that conform to all the standards? – kab00m May 21 '20 at 21:42
  • That is my observation about what I have seen others do. In the (extremely large) company where I work, we do not mess with such details. In the various standard network topologies we have for sites, we are more concerned about having a route, and there will only be two possible ways the route could be pointed. More in depth analysis would be to look at the OSPF or BGP tables, and those would be looking at the assigned Router IDs. – Ron Maupin♦ May 21 '20 at 21:50

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