IPv4 Subnet - /31 (2 IPs) setup help

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aj6828

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#311666 5-Feb-2024 14:59

Hey fellow Quic members

so here it goes i purchased a IPv4 Subnet - /31 (2 IPs) on my current plan

would anyone know how to configure this on OpenWrt or Mikrotik

this is so confusing to me

Thanks in advance..

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michaelmurfy

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#3191156 5-Feb-2024 15:24

Easy ;) you just use SRC-NAT and DST-NAT rules under the Firewall NAT configuration. Basically the subnet won't get assigned, but will be automatically routed. You can from there have traffic go out one of the IP addresses, or forward in to one of the IP addresses. You use a combo of Filter Rules along with NAT.

These are some of my old screenshots. I don't have a Mikrotik anymore, but here are examples of my old configuration when I was running a Mikrotik:

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aj6828

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#3191331 5-Feb-2024 22:45

michaelmurfy:

Easy ;) you just use SRC-NAT and DST-NAT rules under the Firewall NAT configuration. Basically the subnet won't get assigned, but will be automatically routed. You can from there have traffic go out one of the IP addresses, or forward in to one of the IP addresses. You use a combo of Filter Rules along with NAT.

Thanks so much for the post its still confusing to me tried tinkering around for few hours but failed..

where do i put the 31 subnet they gave me ?

thanks mate really appreciate the help

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michaelmurfy

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#3191334 5-Feb-2024 23:02

No need to put their /31 anywhere as it is just routed to you.

So essentially, SRC-NAT is from the inside of your network out. The rule can consist of an IP address on your network, VLAN, range of IP's etc. But this essentially means your device will go out of that IP to the internet. Handy for Guest Networks as a single example. The third screenshot shows that working. You should always have a "default frame masquerade rule" at the bottom where anything unspecified routes out from your standard IP.

DST-NAT is essentially a port forward in. Under the general tab dst address is the IP address on your /31 you're wanting to use then you specify ports etc - action is dst-nat to your internal IP and port. You still treat your standard IP as per normal.

You can also do 1:1 NAT too if you just wanted to forward an entire public IP to an internal device. Remember though, there is no firewall if you do this:

aj6828

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#3191418 6-Feb-2024 14:19

michaelmurfy:

No need to put their /31 anywhere as it is just routed to you.

So essentially, SRC-NAT is from the inside of your network out. The rule can consist of an IP address on your network, VLAN, range of IP's etc. But this essentially means your device will go out of that IP to the internet. Handy for Guest Networks as a single example. The third screenshot shows that working. You should always have a "default frame masquerade rule" at the bottom where anything unspecified routes out from your standard IP.

DST-NAT is essentially a port forward in. Under the general tab dst address is the IP address on your /31 you're wanting to use then you specify ports etc - action is dst-nat to your internal IP and port. You still treat your standard IP as per normal.

You can also do 1:1 NAT too if you just wanted to forward an entire public IP to an internal device. Remember though, there is no firewall if you do this:

legend Thanks, i did 1:1 forwarding since its so complicated for me..

i still cannot get any incoming pings i wonder if there is a provisioning error

thanks mate

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