How to add a routing rule that only match "dport"?
Solution 1:
Add a netfilter mark rule in the FORWARD chain of the mangle table. Then add a routing rule using that mark:
iptables -t mangle -A PREROUTING -s 192.168.28.2 -p tcp --dport 1888 -j MARK --set-mark 0x1/0x1
ip rule add fwmark 0x1/0x1 lookup 123