When i use gateway interface in /ip routes instead just gateway, every ip address which i appeal, gets to my arp table, when i get 8k of them in my arp table, new hosts becоме unavailable, i use MT 3.30, maybe its a bug?

I need the gateway interface option, because both of my external interfaces have same gateway...

This is not a bug, this is the expected behaviour.

In newer versions of RouterOS (including 3.x routing-test) you can specify both interface and nexthop ip address in gateway field (e.g. gateway=1.2.3.4%ether1), maybe this helps?

Thank you very much!!!