Basic NAT Questions

Hi all,

Longtime routing/switching engineer here, but new to Mikrotik. I’ve inherited a network with several routerboards and LOTS of configuration cruft.

Right now I’m looking at some src-nat rules that I don’t think are actually doing anything but wanted to see what longtime Mikrotik users thought. I’ve paired the rules down to include only parameters that have values specified.

Here’s the first example:
action=accept
chain=srcnat
disabled=no
dst-address=10.16.1.0/24
src-address=172.16.11.0/24

As I read this, I don’t see anything for this rule to nat the source to, so I assume this rule (and several others like it) are not doing anything at all.

action=accept
chain=srcnat
disabled=no
dst-address=172.16.11.0/24
src-address-list=localip

Again, it specifies the source as a an address list and the destination as a subnet, but there’s nothing specified for “to-addresses” which I believe is used to specify what the router would actually be changing the packet’s source IP to.

Please let me know if I’m correct or if perhaps there is some other function these rules might serve. I’m happy to supply additional config snippets and command outputs.

Thanks!

No, it does something useful. It accepts matching connections and stops futher processing in same chain, i.e. skips all following rules. In this case it looks like clear attempt to exclude some traffic from srcnat.

Ok, so they are essentially “no-nat” rules, then.

Thanks!