I'm trying to set up a public subnet A.B.C.128/29, the manual implies I need to configure a second LAN, but the tick boxes to enable LAN2, LAN 3 and LAN 4 are greyed out.

Any advice on how to configure a public subnet on the 2830?

MTIA

the solution was to configure the "IP routed subnet" to A.B.C.134 (the router's external address) with a netmask of 255.255.255.248, I'd set the IP address to the network address of A.B.C.128.

This subnet can be configured under the IP routed subnet options within the LAN general setup page.

Alternatively if you wish to use LANs 2,3,4,5,6 then you can enable the VLAN options to un-grey out these options.