point to point router configuration

i have a few questions about a two site point to point setup.

i have two sites: site A - flat network - 172.17.x.x/18 - where the default gateway is the firewall.  site B - flat network - 172.16.x.x/18 - where the default gateway is the firewall.  we currently have a point to point t1 line in place, but it has been giving us problems.  it is a true T1 and was installed four years ago, so the equipment is aging - hence my post... i need to replace the routers on each end and verizon has not been very helpful with pertinent information regarding the circuit.

currently the point to point routers are configured with lan addresses on the inside and are plugged into the network (ex site A - has internal address, site B has internal address and we manage the route through our firewall (routes on either end pointing traffic from one subnet to the next through the lan router address, but are tied to the default lan interface on the gateway).

my questions are:
is this the most effective setup?  i want to know if it would be better to configure the routers to be directly connected to our firewall/gateway and manage the route through the firewall interface (as opposed to the lan address and interface).  if so how should the addressing scheme look?

since this is a closed circuit, do i need ip information from my isp?  or can i make up arbitrary addresses on the same subnet on each end?

i have two cisco 1700 routers each with a csu/dsu card in it.  i'm pretty sure i need the csu/dsu cards to capture traffic on the point to point, but what is the right way to configure the wan(csu/dsu) interface and the lan interface?
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jhaffConnect With a Mentor Author Commented:
thanks for the response.  in my scenario each site also has its own internet connection.  i only want inter-site traffic to flow across the point to point.  

can i set it up like this:

inter-office subnet: (site A) ------ (Site B)

firewall interface address: (site A) and (site B)

then routes setup on each firewall that direct traffic from Site A to Site B through the P2P firewall interface address on firewall A, and vice versa, Site B to Site A through P2P firewall interface address on firewall B.

Or should the P2P routers just be plugged into the existing subnet (172.17.x.x at Site A and 172.16.x.x at Site B) and the route directs traffic to that internal lan address?

Fred MarshallPrincipalCommented:
It seems to me that this is a very reasonable topology.  I'm using exactly the same thing between 3 sites.

If it's a private link provided by the ISP - which may be called MPLS technology or a VLAN or .... then, at least in my case, the inter-office subnet is whatever you want.

So, I have / 24 /24 /24
on the LAN sides.

There is an RV042 router at each side to interface to the links.
The inter-office subnet is: /24

The respective RV042 addresses are:

Because these are not only inter-site links but also are internet links for two of the sites, the main site (with internet gateway) has the RV042 WAN pointing INTO the LAN and the LAN on the interoffice side.
At the other two sites, the RV042 LAN is on the site LAN and the RV042 WAN is on the interoffice side.

The only caution is that the firewalls may have stateful packet inspection on the LAN packets - which will block traffic from site to site.  This has to be turned off.
The RV042s are working in Router mode - no NAT.
Ernie BeekExpertCommented:
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