[colug-432] IPv6 adventures

[R P Herrold]

On Mon, 31 Aug 2015, Rob Funk wrote:

> Jim Wildman wrote:
> > yes.  <dev> of the nic on the ipv6 network
> > 
> > and you need that when ip -6 route doesn't have a default route set
> > yet (because there is no radvd running, no router, etc)
> 
> Hm. If I'm reading it right, both fe80::/64 and my TW-assigned /64
> route to eth0, and I have a default route pointing to my router's
> link-local address (which I still need a -I to ping).

I do not have a reference to an implementation memo or RFC 
'best practices' document, but I believe, in a native ipv6 
environment, that the radvd hands out default routes through 
the link-local IPv6 series, rather than the externally known 
ipv6 address (which may vary over time as links come and go in 
terms of availability)

(from a native ipv6 setup at PMman:

[root at charles ~]# netstat -A inet6 -rn | tail -3 
ff02::1:ffb2:e7f0/128                       ff02::1:ffb2:e7f0                       
UC    0      1        0 eth0    
ff00::/8                                    ::                                      
U     256    0        0 eth0    
ff00::/8                                    ::                                      
U     256    0        0 eth1    

[root at charles ~]# ip addr show eth0
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc 
pfifo_fast state UP qlen 1000
    link/ether 00:16:3e:31:f4:fb brd ff:ff:ff:ff:ff:ff
    inet 198.49.244.251/24 brd 198.49.244.255 scope global eth0
    inet6 2605:4400:1:781:216:3eff:fe31:f4fb/64 scope global dynamic 
       valid_lft 2591943sec preferred_lft 604743sec
    inet6 fe80::216:3eff:fe31:f4fb/64 scope link 
       valid_lft forever preferred_lft forever
[root at charles ~]# 

so: MAC address: 00:16:3e:     31:f4:fb (I set off the last 6 octets)
link-local: fe80::216:3eff: fe 31 f4 fb (so I can show alignment)

and thus its derivation from the MAC address

The link local is 'forever'; the 2605::/16 is mutable, (thus: 
dynamic)

As the 'next hop router' (and usually the radvd)  is always 
accessible in the local network collision domain: 
ff::/8 and fe::/8, this makes sense as an approach

but I write as a practitioner, and not a theoretician

-- Russ herrold