On 2/26/15, 6:03 AM, Eric W. Biederman wrote:

roopa [off-list ref] writes:

quoted

On 2/25/15, 9:19 AM, Eric W. Biederman wrote:

quoted

Unlike IPv4 this code notifies on all cases where mpls routes
are added or removed as that was the simplest to implement.

In particular routes being removed because a network interface
goes down or is removed are notified about.  Are there technical
arguments for handling this differently ? Userspace developers
don't particularly like the way IPv4 handles route removal
on ifdown.

that is true. However, from previous emails on this topic on netdev,
there is no reason to notify these deletes to userspace thereby creating a
notification storm
when userspace can figure this out. Which seems like a valid reason.
(Your approach resembles IPv6 which does generate these notifications and
userspace is usually happy with this).

Grr.  There is an even better way to do this.

The semantically best way to handle this is to simply not use routes for
forwarding where the network inteface is down, the carrier is down, or
the network device has gone away for forwarding.

agreed, And we have an internal patch that does this for regular routing
on carrier down (which we will upstream soon).

Apparently there are some multi-path scenearios that already do this
legitimately, and routes going away auto-matically can cause userspace
other kinds of problems.

In MPLS I especially don't want to free the routing table slot until I
know that the change has propagated in the network and I can be
reasonably confident that no-one will send me traffic on that label.
Otherwise there is a chance the label will be reused too soon.

ack

Grumble.  That is a code change I need to make.  Grumble.

I also need to look and see if those multi-path scenarios report a next
hop as dead or just rely on the network interface state (which I think
it is) to be sufficient information relayed to userspace

they are marked DEAD on ifdown today (AFAIR they dont generate a 
notification in IPv4)  and are skipped during route lookup.
Only when all the nexthops in a multi-path route are dead, is the route 
multipath route declared dead
and is deleted today (with no notification to userspace in the IPv4 case).

Thanks,
Roopa