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Daniel_55334's avatar
Daniel_55334
Icon for Altostratus rankAltostratus
Apr 15, 2015

NAT on LTM or firewall?

We are going to add LTM to a customer network to do outgoing ISP load balance.

 

Internet router --- LTM --- firewall --- core switch

 

Firewall currently performs NAT for outgoing Internet traffic and incoming traffic to web servers. After putting LTM on the network, should such NAT be kept on firewall or be moved to LTM? Which one is the better option?

 

application delivery
design
LTM

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  • BinaryCanary_19's avatar
    BinaryCanary_19
    Historic F5 Account
    Apr 15, 2015

    It's all up to you. If you are not making any decisions based on Source IP, then it doesn't really matter where you NAT.

     

    If you are using for example, Source Address Affinity persistence, then you may want to do the NAT on the LTM.

     

    • dragonflymr's avatar
      dragonflymr
      Icon for Cirrostratus rankCirrostratus
      Apr 16, 2015
      Hi, Maybe I am wrong but if NAT (using F5 definition of NAT) is used to access internal servers then source IP is preserved, only destination IP is changed - Am I wrong? Source IP is changed only if SNAT is used for accessing servers (strange config I guess but possible). I would say that using BIG-IP device to perform just NAT seems to be like not utilizing 99% of features of the device. Not an expert here but I would change this setup so: Internet router --- firewall --- LTM --- core switch Then for outgoing traffic (initiated from LAN to Internet) SNAT can be configured on LTM (probably best practice is rather to set wildcard virtual server (VS)?) For traffic coming from Internet to servers in LAN appropriate VSs should be created. Piotr
    • BinaryCanary_19's avatar
      BinaryCanary_19
      Historic F5 Account
      Apr 16, 2015
      You're not wrong, but most people are not that strict about using the word "NAT". In my experience, it's generally safe to assume that when someone says NAT, then they talking about the F5 SNAT. If I was wrong, I am sure he will clarify, and I will correct my statement to suit.
    • dragonflymr's avatar
      dragonflymr
      Icon for Cirrostratus rankCirrostratus
      Apr 16, 2015
      Good to know, still a lot to learn. I tried to figure out how to configure SNAT to allow access to internal servers that are using private IP - can't find a way :-( I have to be missing something here :-( With servers using public IPs I can figure it more or less but not with private. I will appreciate a lot for any hints how to do such setup. Piotr
  • Daniel_55334's avatar
    Daniel_55334
    Icon for Altostratus rankAltostratus
    May 05, 2015

    If LTM is placed behind firewall, outbound ISP loadbalance cannot be achieved.