ASA 5505 to allow 2nd network segment through mpls

Question

I have been having a heck of a time trying to configure my 5505 to allow the second segment on my network to use the internet.
Office 1 has a fiber internet connection, and all traffic flows fine.
Office 2 had gotten it's internet from AT&T, via a network based firewall injecting a default route into the mpls cloud.
both offices connunicate to each other through the mpls.
When we added the fiber to office 1, we had the mpls people change the default internet route to the inside address of the 5505 and things worked fine.
when AT&T attempted to remove the NBF defaut route, and inject the 5505's address as default, things didn't go so well.
AT&T claims that it is within my nat cmmands on the 5505, but won't tell me anything else.  I assume that they are correct, and I assume that I am not good enough with the 5505 ASDM to tell it what to do.
Office 1 uses 10.10.30.xx addresses and Office 2 uses 10.10.10.xx - the 5505 inside interface is 10.10.30.2 the internal interfaces of the mpls are 10.10.30.1 and 10.10.10.1
I don't know what other information you would need, but am stuck here at Office 1 until I can get this working.
Thanks

Answer 1

Hi,
Ok, so IF I have not understood anything wrong (which is still possible ), it would seem to me that the network mask of the ASA is atleast one reason that will cause problems for WI LAN if they try to use the Internet through the ASA5505 on the PA site.
This is what I would presume will happen when a host on the WI LAN initiates a connection to the Internet
WI PC 10.10.10.10 sends a TCP SYN to initiate/open a TCP connection with a Web server on the Internet
The TCP SYN gets forwarded to the default gateway of the PC which is 10.10.10.1
The TCP SYN packet traverses the ISP MPLS network all the way to the PA Site
The PA Site 3900 has a default route probably towards PA ASA 10.10.30.2
TCP SYN gets forwarded from the PA 3900 to the PA ASA according to the above mentioned default route on the PA 3900
TCP SYN arrives on the ASA and gets forwarded to the Internet
TCP SYN,ACK from the Web server arrives on the ASA
ASA will ARP for the MAC address of the WI PC IP address of 10.10.10.10 because it thinks that the host is directly connected to the ASAs "inside" interface because of the "inside" interfaces large /16 network mask which contains addresses between 10.10.0.0 - 10.10.255.255
The ARP request sent from the ASA never receives a reply since the WI PC isnt directly connected
PA ASA will never be able to forward the traffic to the WI PC which is trying to open the connection to the Internet because of the above mentioned problem. Therefore the TCP connection from WI PC never succeeds and timeouts.
Now you might ask, why does the connections between the PA and WI LAN work. To my understanding is that because the traffic from the PA hosts gets first forwarded to the PA 3900 then they have a working route to the WI LAN. The same way the WI LAN has a working route towards the PA LAN since the ASA isnt not involed in anyway.
The PA Internet connection naturally works as the 10.10.30.0/24 hosts are directly connected to the ASA so the above mentioned ARP will not fail on their part and traffic is forwarded just fine between the PA LAN and the Internet.
So to my understanding the solution to this problem would be to change the PA ASA "inside" subnet mask from 255.255.0.0 to 255.255.255.0.
If you are unsure of the of this change I would suggest you do it when there is low network use (so you can revernt the change) Naturally if you are on the PA LAN then you can probably access the Console connection if something were to go wrong. I cant see any configurations on the PA ASA which would imply that you configure the device remotely through the Internet.
Hope I made sense and hope this helps
Naturally ask more if needed
- Jouni