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New Member

ASA-TMG-CoreSwitch

Hi,I need to introduce a TMG inside one of our branches networks so  the default internet traffic pass through TMG and then to the ASA as per  the new standard. I am new to TMG and playing with few  designs on how  to set TMG up as painless as possible  in to the production environment.

My question is this:

As of now  we have ASA firewall  that connects with a trunk to our  core switch. Vlan x.x.x.x used as a core vlan that the core switch and  ASA being managed through also hosting few lync  servers. Right now ASA  does the NATing for outgoing  internet traffic and  several static NATs for servers on VLANx.x.x.x    What i need is to put a TMG in between ASA and the core switch so all  traffic bound for internet will pass through the TMG while still being  able to keep ASAs internal interface  on VLAN X.X.X.X without being worried about routing issues.

My Idea is to create a new L3 vlan on the core switch (192.168.x.x)  and assign it to the  external interface of the TMG, then give the  Internal Interface of the TMG an IP address within the X.X.X  vlan.  But  without PBR on the core switch  i will cause routing issues if i will  put a default route on the  coreswitch for all  0.0.0.0  traffic to the TMG Internal  and on the  same switch  a Static route for all incoming traffic from the ASA   towards the External TMG.  And if i will extend that 192.168 vlan  in to the Trunk  towards the  ASA i will  have to lose the ASAs interface on vlan X.X.X as to not  cause routing issues with traffic going through ASA towards the TMG. So i  am in a pickle here.... 

how do i preserve ASAs X.X.X interface  and route traffic through it to TMG and back ?

I also will have to disable NAT on TMG so all NAT will be done on the  ASA and  TMG will just be routing all traffic from ASA towards the   X.X.X vlan   through the  Internal Int.  and routing all Internet bound  traffic towards  ASA throught External interface.  I will also have an issue of spoofing  if i will go with my initial config as  vlan X.X.X.X  will be seen on  both internal and external interfaces unless i trunk  it all the way to  ASA.

any ideas will be appreciated.

5 REPLIES
New Member

ASA-TMG-CoreSwitch

If you don't need the X, Y, and Z vlan's to be firewalled you can move them back into the core switch as normal routed vlan's. If you do need one or two of those vlan's to be firewalled you can keep them on the ASA but you won't be able to route their Internet traffic through the TMG - just the internal network(s). You can either put TMG between ASA and core switch which forces you to move X, Y, and Z vlan's to core switch or move TMG between the ASA and the Internet (isn't recommended).

Another solution is to straddle the DMZ and internal networks on the TMG giving it multiple legs. The DMZ leg will connect directly to a DMZ switch feeding the DMZ servers. For this option, your DMZ servers will point their default gateway to the TMG server not the ASA. The ASA will route to the TMG for the DMZ servers on the internal interface. Something like this...

Internet----ASA----TMG----CoreSwitch

                                   |

                                   |

                          DMZSwitch

                                  |

                                  |

                          DMZServers

New Member

ASA-TMG-CoreSwitch

thats where the problem lies...

i have to have Y and Z vlans routed  by ASA (secure segments) and  ASA has to have a leg ( sub int)  in X vlan as if  i need to bypass TMG to staticaly route and staticaly NAT directly to servers in X vlan....

so i am tied by policies of the company and not really able to "move" many things around.

I still have to make sure all default internet traffic  to have the following flow -  Users -> core switch - > TMG --> ASA

while making sure that i have access to ASA ( even throught management interface) from other networks that  are connected or routed to X vlan  by a separate connection ( MPLS)

so in best case scenerio  i can connect management interface  to vlan x  and cut the  vlan x leg off the ASA .. but then i will have two identical routes on ASA:

route (TMG vlan) 10.0.0.0 0.0.0.0 towards the  TMG IP

route (management) 10.0.0.0  0.0.0.0 towards the CoreSwitch.

that brings one more question ...  will the management route create  my routing issues with my  traffic or will the  management-only take care of it  and will only be used to access that interface?

New Member

ASA-TMG-CoreSwitch

Your routing suggestions aren't going to work. The management port is what it is a non-routed port just for directly connected management of the firewall - unless you removed management-only from it.

You can achieve what you're talking about by doing the following design, granted your Y and Z server/LAN traffic will traverse TMG but there's no way around that unless you have a Cisco router in the mix doing some fancy policy based routing. You can still NAT Y/Z servers through ASA and reach the same servers through TMG (without NAT) for internal connectivity and management.

           Y-Servers

                 |

                 |

Internet----ASA----TMG----CoreSwitch----UserVlan's

                 |

                 |

           Z-Servers

Another solution is you can move Y and Z Servers to their own leg on the TMG but you'll be managing two sets of firewall rules (ASA + TMG) for these servers.

                     Y-Servers

                            |

                            |

Internet----ASA----TMG----CoreSwitch----UserVlan's

                            |

                            |

                      Z-Servers

New Member

ASA-TMG-CoreSwitch

my ascii drawings didn't come out right:

top drawing should show Y/Z Servers hanging off ASA

bottom drawing should show Y/Z Servers hanging off TMG

New Member

ASA-TMG-CoreSwitch

i know that what ever traffic that is going to need to reach my users will have to pass throught TMG if i dont have PBR on my CSW, and i need Manangement  int  on ASA justfor that .. to manage it but   what i encountered was that people comming from networks that  are not directly connected to the  core switch  cannot reach the  ASA by its Management  Interface  unless i put a  route management  x.x.x.x/24  next hop core switch IP on X vlan. ( as in ASA doesnt know what lies behind the core switch on management and tries to push all traffic throught the  TMG.

So my question is  if i have two  routes on ASA one on TMG vlan and one on management interface  that are practicaly the same  route .... will ASA know not to push any traffic but the management through it  so it wont cause any issues for me but mgmt int will still be available from remote networks? ( by remote i mean  MPLS behind the core switch , and not through vpn/ASA)

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