No ping behind second AccessPoint

I have a main router There are connected some clients.I have a second wlan router in relay-mode. The second router becomes an dhcp ip ( ), from my main router. The clients behind the second router becomes an ip from my main router of the same subnet e.g.
The clients behind my main router, becomes of couse a dhcp ip from the same subnet, too e.g.
I can ping from to without problems but I cant ping from to
Anybody knows, why I cant ping from to

Sounds like you want a dumb AP configuration. For this, your routers will be connected LAN <-> LAN and your second router will simply be a wired-to-wifi bridge.

BTW, if your CIDR range is /24 (subnet mask, the IP .0 will be invalid for a host.

No, I want an wifi-to-wifi-bridge. Is that possible? Now, Iam using WDS. But on WDS I have to set the second wlan router to a fix ip, of my network. But I works ...

There are 3 ways to make a wifi-to-wifi bridge

  1. WDS -- easiest, may have some difficulties if you are running vendor/other firmware on the primary router/AP (some vendor implementations have quirks or aren't quite to spec). There is a performance penalty of 50%.
  2. Relayd - this is fairly complex and has a bunch of potential issues such as DHCP requests failing. If WDS is supported, don't use relayd.
  3. Mesh this is often a higher performance option, but often requires that your devices are both running the same firmware or at least both have compatible implementations. This also requires multi-radio routers/APs as one of the radios is used purely for backhaul. Again, this is more complex than WDS, but if your hardware supports it, it can be a good option.

On both routers the OS is openWRT 21. But the second router have low memory ( 8MB ).

I don't know how much memory the mesh related packages require, but do both devices have multiple radios?

root@OpenWrt:~# iw list | grep "Supported interface modes" -A 9
	Supported interface modes:
		 * IBSS
		 * managed
		 * AP
		 * AP/VLAN
		 * monitor
		 * mesh point
		 * P2P-client
		 * P2P-GO
		 * outside context of a BSS

I'm running 802.11s mesh and multipe accesspoints (SSID) in one radio in multiple openwrt routers.