[OpenWrt-Devel] Lantiq xrx200: PTM issues

Martin Schiller ms at dev.tdt.de
Mon Jan 20 01:09:30 EST 2020


I have discovered the following problem:

If you have established a PPPoE session via VDSL / PTM connection incl.
VLAN tagging and send data with a relatively small send buffer
(SO_SNDBUF), then an ENOBUFS always comes back.

We first noticed this with stagnating data transfers over an OpenVPN

Also with iputils-ping, since by default the send buffer is relatively

You can also force this with busybox ping by using

echo "5000"> / proc / sys / net / core / wmem_default

minimizes the system default value.

Then you send pings with a packet size of e.g. 4000 bytes and the
second package is already in the pants:

root @ OpenWrt: ~ # ping -s4000
PING ( 4000 data bytes
4008 bytes from seq = 0 ttl = 63 time = 20.519 ms
ping: sendto: No buffer space available
root @ OpenWrt: ~ #

So it should be easily reproducible for everyone.

Traffic that is only routed through the router is not affected.

The manpage of sendto says:
     The output queue for a network interface was full. This generally
     indicates that the interface has stopped sending, but may be caused
     by transient congestion. (Normally, this does not occur in Linux.
     Packets are just silently dropped when a device queue overflows.)

But all former packets have already been transmitted.

This issue seems to be in there since lede-17.01.

I can't reproduce it with owrt-15.05.

Does anyone have any idea how to solve the problem?


openwrt-devel mailing list
openwrt-devel at lists.openwrt.org

More information about the openwrt-devel mailing list