[LARTC] Problem with duplicate route entry (2. TRY) / Route on

[Sven Anders <anders@anduras.de>]

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Hello!

* I modified this a little bit and added some command to make it clearer. *

I have a problem with a duplicate route entry, when using a pre-installed route
and automatic take-over by the "heartbeat" daemon, which adds an address and
the kernel adds an route automatically.

Maybe anyone has an explanation...


> ip addr
1: lo: <LOOPBACK,UP> mtu 16436 qdisc noqueue
    inet 127.0.0.1/8 scope host lo
2: eth0: <BROADCAST,MULTICAST,UP> mtu 1514 qdisc pfifo_fast qlen 1000
    inet 10.10.20.100/32 scope global eth0
> ip route
127.0.0.0 dev lo  scope link
10.10.20.0/24 dev eth0  scope link
default via 10.10.20.1 dev eth0

- -- Now I add a route for my ha net:

> ip route add 10.100.0.0/24 dev eth0 proto kernel scope link
> ip route
127.0.0.0 dev lo  scope link
10.10.20.0/24 dev eth0  scope link
10.100.0.0/24 dev eth0  proto kernel  scope link
default via 10.10.20.1 dev eth0

- -- The 'heartbeat' will add an address on switch-over:
> ip addr add 10.100.0.1/24 brd 10.100.0.255 dev eth0
ip addr
1: lo: <LOOPBACK,UP> mtu 16436 qdisc noqueue
    inet 127.0.0.1/8 scope host lo
2: eth0: <BROADCAST,MULTICAST,UP> mtu 1514 qdisc pfifo_fast qlen 1000
    inet 10.10.20.100/32 scope global eth0
    inet 10.100.0.1/24 brd 10.100.0.255 scope global eth0
> ip route
127.0.0.0 dev lo  scope link
10.10.20.0/24 dev eth0  scope link
10.100.0.0/24 dev eth0  proto kernel  scope link
10.100.0.0/24 dev eth0  proto kernel  scope link  src 10.100.0.1
default via 10.10.20.1 dev eth0

My question is:
 Why did the kernel add a duplicate routing entry, shouldn't it notice the
 existance and avoid this??
 Is this a bug of the kernel?


| "Radoslaw Horodniczy" answered:
|
| This is not a bug, as you see there are 2 different routes


Ok, then try this:

> ip route del 10.100.0.0/24 dev eth0  proto kernel  scope link
> ip route
127.0.0.0 dev lo  scope link
10.10.20.0/24 dev eth0  scope link
10.100.0.0/24 dev eth0  proto kernel  scope link  src 10.100.0.1
default via 10.10.20.1 dev eth0

Now I removed my manually set route. It succeeds.

If I then try to readd it, it fails. But why?

> ip route add 10.100.0.0/24 dev eth0 proto kernel scope link
RTNETLINK answers: File exists

I thought they are different!?!
Is here any difference I did not see?
If they are not different, why does the kernel not recognize it
(see above) and avoid the duplicate entry?

- --------

Another question:

 Why can't I set a route on an interface that is down?
 I can set an address, so why not a route?
 I there a reason for that?

Example:
> ip link set down dev eth0
> ip addr add 10.100.0.1/24 dev eth0
> ip route add 10.100.0.0/24 dev eth0  proto kernel  scope link
RTNETLINK answers: Network is down

- --------

PS: I'm running Linux 2.6.15.1


Regards
 Sven Anders

- --
 Sven Anders <anders@anduras.de>                 () Ascii Ribbon Campaign
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