Subject: Re: [PATCH net-next 0/5] net: Extend address label support

From: Petr Machata <[email-masked]>
Date: Mon, 13 Mar 2023 14:17:25 +0100

Stephen Hemminger <[email-masked]> writes:

> On Fri, 10 Mar 2023 12:44:53 +0100
> Petr Machata <[email-masked]> wrote:
>
>> IPv4 addresses can be tagged with label strings. Unlike IPv6 addrlabels,
>> which are used for prioritization of IPv6 addresses, these "ip address
>> labels" are simply tags that the userspace can assign to IP addresses
>> arbitrarily.
>> 
>> IPv4 has had support for these tags since before Linux was tracked in GIT.
>> However it has never been possible to change the label after it is once
>> defined. This limits usefulness of this feature. A userspace that wants to
>> change a label might drop and recreate the address, but that disrupts
>> routing and is just impractical.
>> 
>> IPv6 addresses lack support for address labels (in the sense of address
>> tags) altogether.
>> 
>> In this patchset, extend IPv4 to allow changing the label defined at an
>> address (in patch #1). Then, in patches #2 and #3, extend IPv6 with a suite
>> of address label operations fully analogous with those defined for IPv4.
>> Then in patches #4 and #5 add selftest coverage for the feature.
>> 
>> An example session with the feature in action:
>> 
>> 	# ip address add dev d 2001:db8:1::1/64 label foo
>> 	# ip address show dev d
>> 	4: d: <BROADCAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc [...]
>> 	    link/ether 06:29:74:fd:1f:eb brd ff:ff:ff:ff:ff:ff
>> 	    inet6 2001:db8:1::1/64 scope global foo <--
>> 	    valid_lft forever preferred_lft forever
>> 	    inet6 fe80::429:74ff:fefd:1feb/64 scope link d
>> 	    valid_lft forever preferred_lft forever
>> 
>> 	# ip address replace dev d 2001:db8:1::1/64 label bar
>> 	# ip address show dev d
>> 	4: d: <BROADCAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc [...]
>> 	    link/ether 06:29:74:fd:1f:eb brd ff:ff:ff:ff:ff:ff
>> 	    inet6 2001:db8:1::1/64 scope global bar <--
>> 	    valid_lft forever preferred_lft forever
>> 	    inet6 fe80::429:74ff:fefd:1feb/64 scope link d
>> 	    valid_lft forever preferred_lft forever
>> 
>> 	# ip address del dev d 2001:db8:1::1/64 label foo
>> 	RTNETLINK answers: Cannot assign requested address
>> 	# ip address del dev d 2001:db8:1::1/64 label bar
>
> This would add a lot of naming confusion with existing IPv6 address labels.
> And MPLS labels.

The confusion, if any, already exists. ip-address just describes address
labels without any regard to ip-addrlabel, and vice versa. I can
actually add verbiage here to make it clear that these are separate
concepts. Likewise for UAPI headers.

> See man ip-addrlabel for more info.  Can't think of better term for this.
> Tag would raise conflicts with vlan/vxlan tag term.
> Name would be confusing vs DNS naming.
>
> Also, most of the real world manages addresses through automated services so
> doing it with ip address isn't going to help.

Yeah. IFA_LABEL exists now, and likely isn't going away.

FWIW I think all it takes to clear up any confusion is a bit of
documentation in man pages and headers.