Best practice for setup of a /27 network

  • Hi everyone,

    Let's say I have a network like Which usable IP should be set to WAN interface? Is there a best practice or required rule that asks for either one of those IPs to be main and rest virtual IPs?


  • Are you getting your IP's via transit network?

  • Not sure what transit network is. I am told its static routing and server is in datacentre.

  • You often get a separate subnet where the gateway lies so you can use the whole subnet.
    I use the first usable next to the gateway. Convention is to use the first or the last usable- on 0/27 that's either 1 or 30. I tend to go with the first.

  • Using the first usable for the router allows you to subdived the IP block later if required without having to change the router IP.

    As an example, say you had.

    Network  =
    Broadcast =
    Usable = to (30 Hosts).

    If you make the router and allocate hosts from that IP upwards, you can always decide later to split that IP allocation between two /28s. (assuming you've not gone past 14 hosts) &

    If you'd placed the router at and then wanted to split the subnets, you'd have to re-ip the router and all the host config that used it  This may not be so much of an issue for a /27 but scale that up to a /24 or /23 and it soon becomes a right royal pain in the ….

    It is for this reason that I would always set the router/Firewall/HSRP etc IPs at the start of the subnet block rather than then end.

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