[GLLUG] basic IPv6 questions

Carles Pina i Estany carles at pina.cat
Sun Oct 3 12:58:51 UTC 2021


If I remember correctly I've seen excellent threads here about ipv6 (and
ipv4 :-) ). I'm now (yes, very late) starting to use ipv6 myself and I
thought of asking a few things to learn it a bit better.

I have a Raspberry pi connected to a BT router that recently has
"switched" to ipv6 only (yay?!). This is helping me to test a Gandi
server ipv6 configuration.

Raspberry pi: /sbin/ifconfig eth0:

eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet6 fe80::56d8:5a6c:fc11:16f1  prefixlen 64  scopeid 0x20<link>
        inet6 2a00:23c6:2c01:b801:2817:ffe3:d3aa:5d8c  prefixlen 64  scopeid 0x0<global>
        ether b8:27:eb:b0:9d:76  txqueuelen 1000  (Ethernet)

I've also have a Gandi server with ipv4 and ipv6 (I've been setting up
the ipv6 parts: enabling it on postfix, SPF, nginx SSL certs using the
ipv6 binding port as well, etc.).

Gandi server: /sbin/ifconfig eth0:
eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet  netmask  broadcast
        inet6 2001:4b98:dc2:53:216:3eff:fe82:b1fb  prefixlen 64  scopeid 0x0<global>
        inet6 fe80::216:3eff:fe82:b1fb  prefixlen 64  scopeid 0x20<link>
	ether 00:16:3e:82:b1:fb  txqueuelen 1000  (Ethernet)

My understading / questions all mixed up (please correct me if I'm
wrong, or confirm?):
-inet6 2a00 and 2001 ipv6 addresses: they are global ipv6 routeable from
 the internet (google.com is 20aa:..., dns.google is 2001:...).
 by the DHCP server of each network (or static configuration).
-Any difference between 2a00 and 2001? Any other addresses like this?
-From the server I would be able to ping
 2a00:23c6:2c01:b801:2817:ffe3:d3aa:5d8c if BT wanted (can I ask them?
 is it in the router configuration? Doing a traceroute I don't quite get
 into the local home router IP, I don't think so)
-fe80:: are local in the network IPs. For Gandi: this gets generated out
 of the MAC address. And not for the Pi, why not? (how to set this up?)

About the routing:

In the Raspberry Pi I see:
pi at raspberrypi:~ $ /sbin/route -n -6
Kernel IPv6 routing table
Destination                    Next Hop                   Flag Met Ref Use If
::1/128                        ::                         U    256 2     0 lo
2a00:23c6:2c01:b801::/64       ::                         U    202 1     0 eth0
fe80::/64                      ::                         U    256 5     0 eth0
fe80::/64                      ::                         U    256 1     0 tun0
::/0                           fe80::ee6c:9aff:fea3:a231  UG   202 5     0 eth0
::1/128                        ::                         Un   0   7     0 lo
2a00:23c6:2c01:b801:2817:ffe3:d3aa:5d8c/128 ::                         Un   0   3     0 eth0
fe80::56d8:5a6c:fc11:16f1/128  ::                         Un   0   4     0 eth0
fe80::e573:8e71:2128:3a11/128  ::                         Un   0   2     0 tun0
ff00::/8                       ::                         U    256 6     0 eth0
ff00::/8                       ::                         U    256 1     0 tun0
::/0                           ::                         !n   -1  1     0 lo
pi at raspberrypi:~ $ traceroute -n -6 google.com
traceroute to google.com (2a00:1450:4009:817::200e), 30 hops max, 80 byte packets
 1  2a00:23c6:2c01:b801:ee6c:9aff:fea3:a231  5.056 ms  4.732 ms  4.549 ms

I'm not quite matching the first hop with the routing table. Why not? In
ipv4 I would be able to see the gateway there (unless the gateway is not
answering ICMP, but if it's fe80::ee6c:9aff:fea3:a231 it does answer

If you have some good resource that answers all of this: please let me
know and I'll happily read. I've been Googling a bit and not finding

Thank you every so much!

Carles Pina i Estany

More information about the GLLUG mailing list