Subject: Should linux send netlink message as it is deleting that routing entry?

From: zhuyj <[email-masked]>
Date: Thu, 10 Apr 2014 16:23:26 +0800

Hi, David

With ubuntu 12.04, I run the following to reproduce this defect.

1) Configure an interface
ifconfig eth1 150.0.0.1/24 up

2) Add routing entry via that interface address
route add -net 200.0.0.0/24 gw 150.0.0.1

3) Change the ip address on that interface as shown below.
ifconfig eth1 151.0.0.1/24 up

4) Check netlink messages with "ip monitor all". There is no route 
delete netlink message.

[ADDR]Deleted 3: eth1    inet 150.0.0.1/24 brd 150.0.0.255 scope global eth1
[ROUTE]Deleted 150.0.0.0/24 dev eth1  proto kernel  scope link  src 
150.0.0.1
[ROUTE]Deleted broadcast 150.0.0.255 dev eth1  table local  proto 
kernel  scope link  src 150.0.0.1
[ROUTE]Deleted broadcast 150.0.0.0 dev eth1  table local  proto kernel  
scope link  src 150.0.0.1
[ROUTE]Deleted local 150.0.0.1 dev eth1  table local  proto kernel scope 
host  src 150.0.0.1
[NEIGH]224.0.0.251 dev eth1 lladdr 01:00:5e:00:00:fb NOARP
[NEIGH]224.0.0.22 dev eth1 lladdr 01:00:5e:00:00:16 NOARP
[ADDR]3: eth1    inet 151.0.0.1/16 brd 151.0.255.255 scope global eth1
[ROUTE]local 151.0.0.1 dev eth1  table local  proto kernel  scope host  
src 151.0.0.1
[ROUTE]broadcast 151.0.255.255 dev eth1  table local  proto kernel scope 
link  src 151.0.0.1
[ROUTE]151.0.0.0/16 dev eth1  proto kernel  scope link  src 151.0.0.1
[ROUTE]broadcast 151.0.0.0 dev eth1  table local  proto kernel scope 
link  src 151.0.0.1
[ADDR]Deleted 3: eth1    inet 151.0.0.1/16 brd 151.0.255.255 scope 
global eth1
[ROUTE]Deleted 151.0.0.0/16 dev eth1  proto kernel  scope link  src 
151.0.0.1
[ROUTE]Deleted broadcast 151.0.255.255 dev eth1  table local  proto 
kernel  scope link  src 151.0.0.1
[ROUTE]Deleted broadcast 151.0.0.0 dev eth1  table local  proto kernel  
scope link  src 151.0.0.1
[ROUTE]Deleted local 151.0.0.1 dev eth1  table local  proto kernel scope 
host  src 151.0.0.1
[NEIGH]224.0.0.22 dev eth1 lladdr 01:00:5e:00:00:16 NOARP
[ADDR]3: eth1    inet 151.0.0.1/24 brd 151.0.0.255 scope global eth1
[ROUTE]local 151.0.0.1 dev eth1  table local  proto kernel  scope host  
src 151.0.0.1
[ROUTE]broadcast 151.0.0.255 dev eth1  table local  proto kernel scope 
link  src 151.0.0.1
[ROUTE]151.0.0.0/24 dev eth1  proto kernel  scope link  src 151.0.0.1
[ROUTE]broadcast 151.0.0.0 dev eth1  table local  proto kernel scope 
link  src 151.0.0.1

There is no netlink message to notify that 200.0.0.0/24 is deleted. But 
in fact, this 200.0.0.0/24 route item disappears.

I checked the source code, and I found the following is the process to 
delete static routes when the attached interface is deleted.

  1)               |  fib_netdev_event() {
  1)               |    fib_disable_ip() {
  1)   1.284 us    |      fib_sync_down_dev();
  1)               |      fib_flush() {
  1)               |        fib_table_flush() {
  1)   0.129 us    |          fib_release_info();
  1)   0.351 us    |          fib_release_info();
  1)   4.605 us    |        }
  1)               |        fib_table_flush() {
  1)   0.096 us    |          fib_release_info();
  1)   0.255 us    |          fib_release_info();
  1)   4.770 us    |        }
  1) + 11.787 us   |      }
  1) ! 315.273 us  |    }
  1) ! 315.888 us  |  }

But there is no netlink message sent here.

Should linux send netlink message as it is deleting that 200.0.0.0/24 
routing entry?

Best Regards!
Zhu Yanjun