FWSM Transparent firewall query

Unanswered Question
Oct 29th, 2007
User Badges:

Customer has over 50 vlans with fwsm inside as below.

WAN --- MSFC ---IDSM-2 --- FWSM --- Inside network (multiple vlans)

Customer wants all internal vlan communication to be inspected by FWSM. What will be the best option - transparent firewall or routed mode and how will this work?



  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)
Jon Marshall Mon, 10/29/2007 - 00:56
User Badges:
  • Super Blue, 32500 points or more
  • Hall of Fame,

    Founding Member

  • Cisco Designated VIP,

    2017 LAN, WAN

Hi Vinod

I would suggest using routed mode. The outside interface of your FWSM will be in the same IP subnet as the MSFC interface but in a different vlan ie. you create 2 vlans with the same IP subnet, the MSFC is in one vlan and the FWSM is in the other vlan and you bridge the 2 vlans together with the IDSM-2 eg.

MSFC ( - vlan 10) -> IDSM-2 -> ( - vlan 11) FWSM.

With this setup all traffic to any of the FWSM inside vlans will have to go through the IDSM-2 and then through the FWSM.



vinod.rathi Mon, 10/29/2007 - 04:58
User Badges:

Hi Jon,

Thanks for your valuable suggestion.

My customer has FWSM IDSM and NAM module with 6500 switch and has the following requirement.

1- Inter VLAN communication needs to be protected by FWSM and IDSM (only inline mode). I have never seen IDSM-2 with inline setup in any of my previous HLD's.

2- Customer has collapsed core architecture with access switches terminating at 6509 directly to FWSM (facing inside). With FWSM running inside, I only have 2 options for redundancy. Either use routed mode and run ospf at the access layer (eigrp not supported on FWSM) or run FWSM in transparent mode.

If you have ever faced such scenario, would appreciate if you could share your experience.




This Discussion