[Kde-hardware-devel] IPv6 basics

[Stefan Winter]

> manually_configured_addr. I'll send an ifconfig output of my work
> workstation tomorrow to illustrate this.

Ah, the wonders of VPN and SSH. So here's a typical ifconfig for dual-stack 
(IPv4 and IPv6) interfaces even before I get back to work:

aragorn ~ # ifconfig
eth0      Link encap:Ethernet  HWaddr 00:05:5D:A1:C5:41
          inet addr:158.64.1.155  Bcast:0.0.0.0  Mask:255.255.255.192
          inet6 addr: 2001:a18:1:8::155/64 Scope:Global
          inet6 addr: 2001:a18:1:8:205:5dff:fea1:c541/64 Scope:Global
          inet6 addr: fe80::205:5dff:fea1:c541/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:4510250 errors:0 dropped:0 overruns:0 frame:0
          TX packets:4825893 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:2615569527 (2494.4 Mb)  TX bytes:654655630 (624.3 Mb)
          Interrupt:16 Base address:0x4f00

(Oops, I should fix my IPv4 broadcast address)

As you see, auto-configured addresses look sucky 
(2001:a18:1:8:205:5dff:fea1:c541/64). That's why I configured a different 
one. Has the advantage that the address is constant even when the hardware 
changes. And that this constant IP address has a reverse DNS entry, as 
opposed to the dynamically generated one. Opposed to IPv4, the idea of having 
more than one layer 3 address is in IPv6 pretty much since day 1.
In Solid, I would need to store three IPv6 addresses and thus a QStringList, 
and this is not a server usage case, but a simple workstation.

And here you see why it's handy to have the pretty-print interface name handy 
for link-local addresses (pinging a different workstation on the LAN):

aragorn ~ # ping6 fe80::200:e2ff:fe95:4a8f
connect: Invalid argument

aragorn ~ # ping6 -I eth0 fe80::200:e2ff:fe95:4a8f
PING fe80::200:e2ff:fe95:4a8f(fe80::200:e2ff:fe95:4a8f) from 
fe80::205:5dff:fea1:c541 eth0: 56 data bytes
64 bytes from fe80::200:e2ff:fe95:4a8f: icmp_seq=1 ttl=64 time=0.222 ms

A ping request without the interface identifier just is not a valid operation 
with IPv6 if the address to be pinged is a link-local one. Scope Id's are 
important in that case (though I'll admit they are seldomly used).

Greetings,

Stefan

-- 
The K Desktop Environment
- Stefan Winter -
Areas of Activity:
kdenetwork/wifi (KWiFiManager)
kde-i18n/de (German translation)
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