[kvach]

Firmware: DD-WRT v24-sp2 (03/25/13) mini,
I`m only getting ~100mbps on 1gig wan connection. How can I improove it? I can see 1gig link on lan-pc as well as 1gig ISP-wan link.
When I connect directly(without router) I have good speeds.

[ddaniel51]

The M20 was not designed for 1gbs speeds. You need a more powerful router.

The Netgear R7800 with Kong's build is a great router for 1gbs service.

[kvach]

but it advertised as 1gig router, I can understand that it won`t achieve full gig, but why ddwrt limits to 100mbps?

[ddaniel51]

True it has 1gb ethernet ports but, it does not have the processing power to pass 1gb WAN bandwidth.

DD-WRT being software does impose a bandwidth penalty usually in the area of 50% of what stock factory software can do. It's a tradeoff for the features it brings you.

The M20 in stock form would be lucky to do 200mb WAN throughput. It's little brother the M10 has the same processing power along with 100mb Fast ethernet ports.

Today's fastest routers still have 1gb ethernet ports but, they are increasing their processing power to manage faster WAN internet throughput.

The M20 has a 300mb single core cpu while the R7800 has a 1.7gb dual core cpu. Which one is going to pass more internet throughput?

The M20 is 7 years old and was ok for slow internet. Advances in internet bandwidths and Wifi has left it behind.

You want more throughput from your M20? Go back to stock firmware.