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

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

Quoted 8 lines

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

Quoted 6 lines

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.

Quoted 8 lines · On Fri, 11 Apr 2014 17:15:48 +0800 zhuyj <[email protected]> wrote:

Quoted 8 lines

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

Quoted 6 lines

Quoted 6 lines

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.

With IPv4 there are several cases where there is a non-notified implicit route withdrawal. This is not something that can be fixed. There are two issues:
1. with large backbone size route tables (ie 1M routes), the number of notification messages becomes a bottleneck and would be unreliable
2. the existing routing daemons (quagga, bird, etc) all understand/expect the existing semantics