Adding network switch to external WAN to increase number of ports available

Question

This may be a stupid question but this has kinda been landed on me so I'll ask anyway.
We have a Cisco router with ethernet connection to our provider's NTE.  They provide us with one ethernet port on the NTE which we connect to the WAN port on our Cisco router. The WAN interface on our router is configured with a public IP address from the /29 subnet the provider assigned to us.
We have a 3rd party installing SIP connectivity for us and they need us to provide them with a public IP address and connectivity outside our router/firewall for their Session Border Controller (apparently NAT doesn't work well with SIP so we can't have it inside our network and NAT it via our existing router)
Since we only have one ethernet port presented to us by our provider, is this just a case of placing a network switch in between the router and the provider NTE then having our router connect to the switch and the 3rd party's Session Border Controller connect into the switch too?  We can then assign another IP address from our provider's /29 to the 3rd party's kit.
Is it as simple as that or am I missing something?
If it really is that simple, are there any considerations for what sort of switch I should use?  Can it be something relatively cheap and cheerful, does it even need to be a managed switch?  

Answer 1

Is it as simple as that or am I missing something?
Should be that simple although I would check with provider ie. a switch will usually send L2 protocols on the link to the provider as well as to the router so you may want to check with them they are happy for you to do it.
Although I suspect they won't care as they don't really know how you have it connected now ie. you could already be using a switch as far as they know.
Still worth running it by them though.
You only need a L2 switch so definitely no need for L3 functionality.
Some people prefer unmanaged switches outside of their network eg. in the untrusted area.
Really up to you whether you need it managed or not.
In terms of overall functionality very little is needed but you would want something reliable as it is another single point of failure.
One last thing, if this is the only connection then nothing else to do but be aware that currently if the provider NTE fails your router knows about it because it is a direct connection. With a switch in between if either side fails the other side doesn't know because it's connection to the switch is still up.
If this is your only connection to the internet then it's not an issue but if you had an alternate path you would need to track the connection to make sure you failed over properly.
Jon