How to Configure Router for Metro Ethernet - which router to choose ?

I am not a router expert!    So, I am running a simple business network:  35 PC's including 2 servers behind a Juniper NS5GT "router/firewall" - using NAT (internally everyone is 192.168.0.x).    Email is routed through the firewall to the exchange server.   Majority of usage is outbound web browsing.

So, we have ordered and had installed a new 10MB Metro Ethernet fiber link from Comcast.   This fiber link will also be handling the phones - but that is not my concern at this time.

Here's the problem:   Comcast is giving me a WAN block of IP addresses as well as a LAN block of IP addresses.
WAN Block:  50.207.18/212/30  (GW is the .213, IP is .214)
LAN Block:      Usable: .241 thru .246

So...    Can I use the Juniper NS5GT ?     How can I configure it to do the job?   I thought at first that I could just ignore the LAN Block and assign the Juniper the address with gateway   In fact, I tried that with a Cisco RV120W (spare available to me to test at the time) and it seemed to work.   However, Comcast is telling me that this is not a valid configuration.   Thoughts?

If the Juniper 5GT will not work, which router would you recommend for this very simple configuration?
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JohnBusiness Consultant (Owner)Commented:
I use Juniper NS5GT and later SSG5 at clients. The configuration you have for one IP and gateway should be valid. For the IP, I would just use a single IP and not a range. Perhaps that is what Comcast is referring to .
ponedogAuthor Commented:
John Hurst:   Are you on a Metro Ethernet link as well (with both a WAN block and a LAN block)?
JohnBusiness Consultant (Owner)Commented:
No. I am in a different country in North America and the local ISP's are not Metro Ethernet.

However my clients have a block of several IP addresses and I just use one.
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ponedogAuthor Commented:
John Hurst:  thanks for your comments.   However, the key problem here is that the WAN Block and the LAN Block are 2 different disjoint block of addresses.  I am not sure how to tell the Juniper how to handle this situation...
JohnBusiness Consultant (Owner)Commented:
Juniper NS needs one IP from the WAN Block  the same as you had before Metro. Same settings except use

The LAN block is of course different. That is the internal setup 192.168.0.x as before. In theory, nothing here changes.

The only change is the hookup to the WAN.

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ponedogAuthor Commented:
John Hurst:   I just talked to a support engineer at Comcast.   Given our needs, he said that we can just ignore the LAN IP block (hmmm....   I think that is exactly what you said!).      I am closing the case and awarding the points to you - thanks a million !!
JohnBusiness Consultant (Owner)Commented:
@ponedog  - Thanks for the update and I was happy to help.
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