NM 0.7 : how to add routes?

From command line i use this :
route add -net 192.168.0.0 netmask 255.255.240.0 gw 192.168.6.2 dev eth0

i want to do this through the Network manager Gui options but i'm a little confused about how to add routes.
i edit eth0 through NM 0.7 , i go to 'Ipv4 Settings' Tab and i click on 'routes' .
Then i see this :

      Address | Prefix | Gateway | Metric

but where i have to put the netmask ???
in 'prefix' maybe ? if yes in what format?

Question information

Language:
English Edit question
Status:
Solved
For:
Ubuntu network-manager Edit question
Assignee:
No assignee Edit question
Solved by:
Albert Damen
Solved:
2008-09-15
Last query:
2008-09-15
Last reply:
2008-09-03
Best Albert Damen (albrt) said : #1

You will need to fill in Prefix. Prefix is a different notation of netmask.
For your netmask 255.255.240.0 the corresponding prefix is 20.

If you want to know why: 255.255.240.0 is written binary as
11111111.11111111.11110000.00000000.

Now count the 1's and you get 20.

Thanks Albert Damen, that solved my question.