On 2019-05-20 22:53, Michal Kubecek wrote:
On Mon, May 20, 2019 at 10:23:03PM +0200, M. Buecher wrote:
Used feature is the label option of `ip`, which works for IPv4, but
not with
IPv6.
The only reason for having these labels is to allow old tools like
ifconfig to partially work even if the underlying implementation
changed. There is no need for labels with IPv6 as even ifconfig (and
the
ioctl interface it uses) does not pretend there are virtual interfaces
and 1:1 mapping between interfaces and addresses and usess add/remove
to
add or remove addresses to/from the list.
Goal: Use virtual interfaces to run separate instances of a service on
different IP addresses on the same machine.
For example with dnsmasq I use `-interface ens192` for the normal main
instance, while using `-interface ens192:0` and `-interfaces ens192:1`
for
special instances only assigned to specific machines via their MAC
addresses.
Configuration syntax based on "listening on an interface" is in most
cases a historical relic because this "interface" is just used to get
the address the daemon is to listen on (bind the listening socket to).
Most daemons support also identifying the listening address(es)
directly
which should be preferred as then your configuration matches what the
daemon is actually doing. (There are exceptions, e.g. "ping -I eth1"
does something different than "ping -I 1.2.3.4" but these are rather
rare.) Any daemon supporting IPv6 should definitely support setting the
listening address(es) directly.
"Listening on an interface" is extremly convenient: configure/change ip
addresses on the "label", then just reload/signal the services.
No tedious tasks needed to define each and every IP address (v4+v6) for
each and every service.
Therefore I prefer the "oldschool" way of "listening on an interface".
Especially with the standard multi-homing of IPv6 I still vote for the
old style and introducing labels also for IPv6.
Otherwise I just have to obey the decisions of the Kernel team and adopt
my setups.
All explanation have been much appreciated from everybody that answered.
This helped me to understand the topic much better. Thanks a lot.
Btw today ping doesn't work anymore with "labels", e.g. "-I eth0:0", as
it incorrectly assumes an IP address due to the colon, although an IPv6
address has always at least two colons in it (::1,
2001:0DB8:3:4:1:2:3:4)
What is the correct name when I use the label option of the ip
command?
The "IP-Aliasing" doc was the only one I could find on kernel.org that
fit
the way labels are assigned with ip.
They are just labels. The term "IP aliasing" denotes the older
implementation in 2.0 kernels where there were actual virtual
interfaces, allowing you to assign the extra addresses to them. Since
kernel 2.2, it's no longer the case, there is just the actual interface
and it has a list of IPv4 addresses.
Michal Kubecek
