Can only ping most-recently associated wireless client

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RayC
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Joined: 19 Apr 2018
Posts: 4

PostPosted: Thu Apr 19, 2018 13:49    Post subject: Can only ping most-recently associated wireless client Reply with quote
I have DD-WRT installed on 4 routers. 2 are Asus RT-AC66U A, 1 is Asus RT-AC66U B (using AC68 firmware), and the other is a Netgear WND4500 V1.

I was using r34411 (Jan 7, 2018) firmware on all of these.

I noticed that I would periodically become unable to access the web page of the router I was connected to. After some investigation, I found that if I made a telnet connection into the router where devices are associated and attempted to ping them that I could _only_ ping the devices that most-recently associated on a given radio and I could _not_ ping the other devices. I _could_ ping those devices from other routers on the network.

In other words, I could only ping 1 device per radio on a given router if the ping was initiated from the router where the devices are associated. It appears to me that whichever device associated last could be pinged while no others could be pinged from the router where they are associated. I could usually ping them from the other routers were they were not associated (other routers on the LAN) and I could ping them from other hard-wired devices.

This failure happened on the Asus RT-AC66U A devices and the Netgear WND4500 V1 device but the Asus RT-AC66U B (running AC68U firmware) worked fine. I noticed that the kernel versions were identical on the failed devices. I also found that I could ping the devices from the router where they were associated if I manually added ARP entries for them, but if I removed the static ARP entries then they, again, became unpingable.

I dropped back to r32170 (was just looking for something around a year old in hopes of finding an older kernel version for them). I reverted to this version with the option set to retain settings and made no modifications to the settings.

Upon reboot with this older firmware, I found the problem was resolved. I put this level of DD-WRT on all of the failed routers and they also work properly.

The AC66U A routers are configured with 2 VLAN IDs and has some level of complexity, but the Netgear WND4500 was configured far more basic (no VLANs, router mode, WAN disabled, nothing particularly exciting). All connect to the rest of the LAN on a LAN port. The WAN port is disabled on all of them. The clients in question were all on br0 across all devices. The wireless connections are not set to be "isolated".

It is my belief that something was modified in the kernel code at some point between r32170 and January of this year that has caused this behavior. I realize that is a pretty broad range of time. I may be able to find some time to narrow it down to a specific DD-WRT release that exhibits this problem, but I maintain these remotely and kind of concerned about flashing too many times remotely in fear that I may grab a bad dd-wrt for the router and lose control remotely.
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