NTL Cable modem question

Can I plug a network switch into the RJ11 port on the back of the cable modem and it'll work, or do I need a router to do this?

I susspect its an RJ45 port and no it wont work, you will need a cable router, sometimes (confusingly) referred to as a cable/DSL router.
Not to be confused with an ADSL router which will be no good to you.

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sometimes (confusingly) referred to as a cable/DSL router

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... or even Broadband routers, no less ambiguously. (To the OP) Have a browse here for example.

What about if I plug a wireless access point into the cable modem?
Would that allow multiple wireless adaptors to access the web or just a single one?

Just a single device, the cable provider will only give out one ip address (TW used to provide 2 if you had a gaming account).

... however using an access point allows you to swap between WiFi clients without having to reboot the cable modem, as long as the access point is configured to present it's own mac address to the modem rather than those of the clients.

Some wireless access points act as DHCP servers (my old Netgear WG602 does) normally the DHCP is disabled allowing the router to supply IP addresses to the network, but if you enabled the DHCP in the access point wouldn

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Some wireless access points act as DHCP servers (my old Netgear WG602 does)

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Are you certain? There have been a number of variants of the WG602, but I've never seen one that provides a DHCP service.

A DHCP service alone wouldn't help anyway, as the cable broadband network wouldn't know anything about the IP addresses allocated by DHCP. You would need address translation (NAT) as well, effectively making the wireless access point into a router rather than a simple access point.

Some wireless access points act as DHCP servers (my old Netgear WG602 does) normally the DHCP is disabled allowing the router to supply IP addresses to the network, but if you enabled the DHCP in the access point wouldn

The DHCP client is different. This is the WG602 itself needing an IP address for management purposes. If it finds a DHCP service on the network then it will allocate it's own IP address from this, if not then it automatically allocates a default static address for it's own management.

There is an obscure reference to the WG602 itself acting as a DHCP server in Appendix C, but this also says that that it provides NAT and at the start of the appendix it talks about the WG602 being a 'small office router'. Strangely though there's nothing elsewhere in the manual about how to configure this capability. I guess that either it has a router mode that can be switched on in an undocumented interface, or the technical author just imported a standard reference section from a router manual and mistakenly swapped the device reference to WG602 rather than referring to an external router. A later version of the manual has this removed entirely, so I suspect it's just a mistake.

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