I add a relation with the feature I asked few days ago. This one express much more clearly the issue than the one I wrote :)

I took what an additional host interface looks like in Foreman today:

[{"name":"s01","ip":"10.7.18.21","id":3,"subnet_id":1,"updated_at":"2013-02-26T18:21:16Z","mac":"00:11:22:33:44:55","attrs":null,"created_at":"2013-02-26T18:21:16Z","domain_id":1,"host_id":34}]

And kind of mocked up an idea of what I was thinking the interface array might look like (with some spaces just for sanity) so that people could do bonding and sub-interfaces. One thing about this is that it includes the 'primary interface', versus how it is outside of the array created today. I guess that's not too much of an issue as long as it can be made part of bonds, etc.

As far as UI, it might be easier to select whether the interface you are creating is a standard interface, bonding slave, bonding master, or sub-interface and filling out any mandatory or optional fields for each that way. I'm not really too worried about Foreman validating the configs that I enter either, though down the road it may be nice. But I don't believe cobbler is doing that right now, probably because it would be a bit difficult to validate.

Also, after talking to Sam today I realized that people might see value in being able to create bridges and assign interfaces to a bridge, and though it is not something we do today, others might certainly see value in that.

[ {"device":"eth0","bonding-opts":"","bonding-master":"bond0","bonding-mode":"slave","name":"somehost","ip":"10.7.18.21","id":3,"subnet_id":1,"updated_at":"2013-02-26T18:21:16Z","mac":"00:11:22:33:44:55","attrs":null,"created_at":"2013-02-26T18:21:16Z","domain_id":1,"host_id":34},

{"device":"eth1","bonding-opts":"","bonding-master":"bond0","bonding-mode":"slave","name":"somehost","ip":"10.7.18.21","id":3,"subnet_id":1,"updated_at":"2013-02-26T18:21:16Z","mac":"00:11:22:33:44:56","attrs":null,"created_at":"2013-02-26T18:21:16Z","domain_id":1,"host_id":34},

{"device":"bond0","bonding-opts":"mode=1 miimon=500","bonding-master":null,"bonding-mode":"master","name":"somehost","ip":"10.7.18.21","id":3,"subnet_id":1,"updated_at":"2013-02-26T18:21:16Z","mac":null,"attrs":null,"created_at":"2013-02-26T18:21:16Z","domain_id":1,"host_id":34},

{"device":"bond0:1","bonding-opts":"","bonding-master":"","bonding-mode":"","name":"somehost-vhost","ip":"10.7.18.22","id":3,"subnet_id":1,"updated_at":"2013-02-26T18:21:16Z","mac":null,"attrs":null,"created_at":"2013-02-26T18:21:16Z","domain_id":1,"host_id":34}
]

This is something that i've created a snippet for, ideally this needs to be a plugin really to foreman, which i did want to create but not had time.

So far i have used parameters defined at a host / host group level.

The layout i chose was:
device_name
device_address
device_gateway
device_netmask

Then for bonding the extras would be:
bond_interfaces
bond_name
bond_options

And for vlans, the extras would be:
vlan_name
vlan_device

i.e. eth1_name, eth1_address , eth1_gateway. eth1_netmask

for bonding it would be

bond0_interfaces="eth0,eth1"
bond0_name="some name of the bond"
bond0_options="mode=1 miimon=100 downdelay=200 primary=eth0"

Or if the bond was to have a specific iP:
bond0_interfaces="eth0,eth1"
bond0_address = "10.123.3.4"
bond0_netmask = "255.255.255.0"
bond0_gateway = "10.123.3.1"
bond0_options = "mode=1 miimon=100 downdelay=200 updelay=200 primary=eth2 use_carrier=1 primary_reselect=2"options
bond0_name = "Some name"

1. Vlan interface with IP configuration
   vlan123_name = "Some vlan name"
   vlan123_device = "bond1"
   vlan123_address = "10.123.3.4"
   vlan123_netmask = "255.255.255.0"
   vlan123_gateway = "10.123.3.1"

1. VLAN interface with no IP config
   vlan1234_name = "Some vlan name"
   vlan1234_device = "bond0"

Basically all of the networking is done at build time so this doesn't need to be managed elsewhere with puppet, which can be a bit of a nightmare to do i.e. rejigging interfaces when puppet requires network connectivity is not always the easiest approach.