Vlan – Need help converting ASA 5505 config to ASA 5512

Best practice wise - should I let the router or the ASA handle NAT (Overloading)?

In the most general of design best practices NAT is performed between an inside and outside network. NAT overloading is generally performed at the edge when there is limited public IP address space. You can learn more about NAT overloading, also known as Port Address Translation or PAT, in RFC 2663 (PAT is referred to as Network Address Port Translation (NAPT) in section 4.1.2).

In this particular scenario you can argue that you have two inside and outside networks and will need to perform some form of NAT on both the ASA (whether that is the NAT overloading you're using now, NAT exemption, static NAT, etc) and the Cisco Router.

I can ping the 172.16.2.2 interface but not 172.16.2.1 from a pc connected to one of the layer 2 switches (proves intervlan routing is working -- i have a 172.20.100.8 address on the PC). Why can't I ping 172.16.2.1 from a PC but I can from the Layer 3 Switch?

The ASA 172.16.2.2 is receiving the ICMP echo-request but does not have a route back to 172.20.100.0/27. The echo-reply is actually being forwarded to the Router 172.16.1.1 via the default route.

And most of all -- Why can't I get out to the Internet from the Layer 3 switch?

Currently your ASA and Cisco Router do not have routes to internal devices other than their connected routes.

Your ASA configuration:

route outside 0.0.0.0 0.0.0.0 172.16.1.1 1

This will provide a default route via the outside interface, but how will the ASA know how to reach subnets residing behind the Layer 3 Distribution Switch?

You'll need to add routes to the internal subnets via the inside interface using the Layer 3 Distribution Switch as the next-hop IP address.

ASA static routing example:

route inside 172.19.12.0 255.255.255.240 172.16.2.2
route inside 172.19.3.0 255.255.255.0 172.16.2.2
route inside 172.20.100.0 255.255.255.224 172.16.2.2

Further reading: ASA static routing

Your Cisco Router's configuration:

ip route 0.0.0.0 0.0.0.0 200.200.200.200

Additionally, how will your border router know how to reach subnets other than it's connected routes, and the catch all default route via the outside interface's next-hop address 200.200.200.200?

Router static routing example:

ip route 172.19.12.0 255.255.255.240 172.16.1.10
ip route 172.19.3.0 255.255.255.0 172.16.1.10
ip route 172.19.100.0 255.255.255.224 172.16.1.10
ip route 172.16.2.0 255.255.255.224 172.16.1.10

Further reading: ISR static routing

I cannot get an ip address right now from the DHCP server (Windows). Any insight into why?

Ensure you have end-to-end IP reachability between the client(s) sending DHCP discover messages and the DHCP server.

From what I can gather from your topology and configuration, the subnets 172.19.3.0/24, 172.19.12.0/28 and 172.20.100.0/27 should have no issues connecting to each other (assuming they are configured to use their respective default gateways) from a networking perspective.

You can remove the ip helper-address syntax from the SVI 100 given that the DHCP server is on the same segment and that command is used for a DHCP server(s) that is on a different segment.

interface Vlan100
ip address 172.20.100.1 255.255.255.224
ip helper-address 172.20.100.27

This is an old question, but I recently ran into this same issue, and after some trial and error, I was able to come up with a solution. The following applies to ASA Version 9.1. I have two VLANs on our network: one for PCs, and one for VoIP. I wanted the VoIP VLAN to use its own outside address, separate from the outside address used by the PCs. Here's what the configuration ended up looking like (IP addresses have been obfuscated slightly). These are only the pertinent parts of the configuration, not a complete dump:

: ASA Version 9.1(2) 

interface Ethernet0/0
!
interface Ethernet0/1
 switchport access vlan 2
!
interface Ethernet0/6
 switchport access vlan 50
!
interface Vlan1
  nameif outside
  security-level 0
  ip address 65.65.65.10 255.255.255.192 
!
interface Vlan2
 nameif net-inside
 security-level 100
 ip address 10.1.10.1 255.255.248.0 
!
interface Vlan50
 nameif net-voip
 security-level 100
 ip address 172.16.0.1 255.255.255.0 
!
object network net-voip
 subnet 172.16.0.0 255.255.255.0
 nat (net-voip,outside) dynamic 65.65.65.20
!
nat (net-inside,outside) after-auto source dynamic any interface
!
dhcpd ping_timeout 750
dhcpd auto_config outside
dhcpd address 172.16.0.100-172.16.0.127 net-voip
dhcpd dns 8.8.8.8 interface net-voip
dhcpd enable net-voip

I also included the part of my configuration which sets up DHCP on the VoIP VLAN for the phones. One snag I ran into (which should've been obvious in retrospect), the net-voip VLAN needs to have a security level higher than the outside VLAN, otherwise it won't be allowed out.