David Ahern says:
====================
net: ipv6: Improve user experience with multipath routes
This series closes a couple of gaps between IPv4 and IPv6 with respect
to multipath routes:
1. IPv4 allows all nexthops of multipath routes to be deleted using just
the prefix and length; IPv6 only deletes the first nexthop for the
route if only the prefix and length are given.
2. IPv4 returns multipath routes encoded in the RTA_MULTIPATH attribute.
IPv6 returns a series of routes with the same prefix and length - one
for each nexthop. This happens for both dumps and notifications.
IPv6 does accept RTA_MULTIPATH encoded routes, but installs them as a
series of routes.
Patch 1 addresses the first item by allowing IPv6 multipath routes to be
deleted using just the prefix and length. Patch 2 addresses the second
allowing IPv6 multipath routes to be returned encoded in the RTA_MULTIPATH.
Patches 3 and 4 upate the RTM_{NEW,DEL}ROUTE notifications to generate
1 notification with RTA_MULTIPATH where applicable.
Patch 5 prints IPv6 addresses in compressed format when showing route
replace errors. This was noticed testing REPLACE failures.
The end result for multipath routes:
1. Dump
- RTA_MULTIPATH used for multipath routes
$ ip -6 ro ls vrf red
2001:db8:1::/120 dev eth1 proto kernel metric 256 pref medium
2001:db8:2::/120 dev eth2 proto kernel metric 256 pref medium
2001:db8:200::/120 metric 1024
nexthop via 2001:db8:1::2 dev eth1 weight 1
nexthop via 2001:db8:2::2 dev eth2 weight 1
...
2. Route Add
- one notification with RTA_MULTIPATH attribute
$ ip -6 ro add vrf red 2001:db8:200::/120 nexthop via 2001:db8:1::2 nexthop via 2001:db8:2::2
$ ip mon route
2001:db8:200::/120 table red metric 1024
nexthop via 2001:db8:1::2 dev eth1 weight 1
nexthop via 2001:db8:2::2 dev eth2 weight 1
2. Route Replace
- one notification with RTA_MULTIPATH attribute
$ ip -6 ro replace vrf red 2001:db8:200::/120 nexthop via 2001:db8:1::16 nexthop via 2001:db8:2::16
$ ip mon route
Replaced 2001:db8:200::/120 table red metric 1024
nexthop via 2001:db8:1::16 dev eth1 weight 1
nexthop via 2001:db8:2::16 dev eth2 weight 1
- on a failure after the insertion of the first nexthop (which means
the original route has been replaced in the FIB), a notification is
sent with the successful nexthops and then the nexthops are deleted
with one notification per hop. This is consistent with how it works
today except the successful additions are coalesced into 1
notification.
3. Route Delete
- delete of entire multipath route using prefix/length only 1
notification is generated:
$ ip -6 ro del vrf red 2001:db8:200::/120
$ ip mon route
Deleted 2001:db8:200::/120 table red metric 1024
nexthop via 2001:db8:1::16 dev eth1 weight 1
nexthop via 2001:db8:2::16 dev eth2 weight 1
- if a delete request contains nexthops one notification is
generated per nexthop deleted. This is unavoidable since IPv6
alllows a single nexthop to be deleted within a multipath route
4. Route Appends
- IPv6 allows nexthops to be appended to an existing route. In this
case one notification is sent for the new route with the append
flag set.
$ ip -6 ro append vrf red 2001:db8:200::/120 nexthop via 2001:db8:2::20 nexthop via 2001:db8:1::20
$ ip mon route
Append 2001:db8:200::/120 table red metric 1024
nexthop via 2001:db8:1::2 dev eth1 weight 1
nexthop via 2001:db8:2::2 dev eth2 weight 1
nexthop via 2001:db8:2::20 dev eth2 weight 1
nexthop via 2001:db8:1::20 dev eth1 weight 1
- on failure of an append, a notification is sent with the route
containing all of the nexthops successfully added, and it is
followed by delete notifications as the hops are removed
returning the route to its prior state. This is consistent with
how it works today except the successful additions are coalesced
into 1 notification.
Addresses some of the inconsistencies also noted by Roopa at netdev0.1:
https://www.netdev01.org/docs/prabhu-linux_ipv4_ipv6_inconsistencies_talk_slides.pdf
v4
- changed series to do encoding in 1 patch and updating notificatons
in separate patches to make it easier to review and understand
- 1 notification for delete when using prefix/length; 1 notification for
append
- handle delete of a single nexthop without RTA_MULTIPATH in delete request
- upated commit messages and cover letter
v3
- removed the need for a user API to opt-in to change. Requiring an
API just shifts the difference from same API with different
behavior to different API to achieve equivalent behavior
- route notifications changed to use RTA_MULTIPATH for add and replace
- upated commit messages and cover letter
v2
- fixed locking in patch 1 as noted by DaveM
- changed user API for patch 2 to require an rtmsg with RTM_F_ALL_NEXTHOPS
set in rtm_flags
- revamped explanation of patch 2 and cover letter
====================
Signed-off-by: David S. Miller <davem@davemloft.net>