In order to do a network installation, you must provide the MAC address of the adapter that you want to boot from.
This information can either be found using the SMS menu or using the Open Firmware prompt.

To show the MAC address of a specific adapter use the dev <DEVICE> .properties command.
FYI: If you are not sure about the <DEVICE>, use ls to get a list of all devices in the system.

0 > dev /vdevice/l-lan@30000004 .properties
ibm,loc-code U9123.710.1008E7A-V3-C4-T1
reg 30000004
ibm,my-drc-index 30000004
ibm,phandle 30000004
interrupts 000a0004 00000000
ibm,#dma-address-cells 00000002
ibm,#dma-size-cells 00000002
ibm,my-dma-window 10000004 00000000 00000000 00000000 10000000
name l-lan
device_type network
compatible IBM,l-lan
local-mac-address ee82a000 3004
mac-address ee82a000 3004
ibm,mac-address-filters 000000ff
ibm,vserver

Another method:
0 > dev packages/gui
ok
0 > display_boot_devices #network

SMS Macro Operation Succeeded.
Device Current Device
Number Position Name
1. 2 Interpartition Logical LAN ( loc=U8246.L2B.06009AA-V1-C3-T1 )
2. – Interpartition Logical LAN ( loc=U8246.L2B.06009AA-V1-C4-T1 )
3. – Interpartition Logical LAN ( loc=U8246.L2B.06009AA-V1-C5-T1 )
4. – Interpartition Logical LAN ( loc=U8246.L2B.06009AA-V1-C6-T1 )
5. – PORT – 1 IBM Host Ethernet Adapter ( loc=U78AB.001.WZSGK0Z-P1-C2-T1 )
6. – PORT – 2 IBM Host Ethernet Adapter ( loc=U78AB.001.WZSGK0Z-P1-C2-T2 )
ok
0 > display_mac_address U78AB.001.WZSGK0Z-P1-C2-T1
SMS Macro Operation Succeeded.
MAC-ADDRESS = 5cf3fc85f240
ok