Posted: Fri Jun 02, 2023 22:12 Post subject: Issues w/ ppp compression (renamed)
Hi,
I've set up a very slow ppp link to receive connectivity from a wireless serial modem. That part works, but it is EXTREMELY slow. The actual baud rate is 38.4k - but the throughput I'm getting is far less, around 8 kbps.
Currently ppp is running with the -noccp flag and an MTU of 296 for reliability (!), since omitting it (and hoping for a small improvement via compression) causes dd-wrt's logs to say
Code:
"ppp0: ppp: compressor dropped pkt"
endlessly and no working connection.
Does ppp on dd-wrt support any kind of compression scheme? I'm not looking for header compression, but data compression. If yes, does it require a certain MTU to work?
Thanks,
R
Last edited by flyingfishfinger on Sun Jun 11, 2023 17:36; edited 1 time in total
Joined: 08 May 2018 Posts: 14221 Location: Texas, USA
Posted: Fri Jun 02, 2023 23:08 Post subject:
BSD PPP compression should be available.... but no detailed information, just a blind question without doing research for yourself. Be happy I obliged the 5 minutes to find these.
Fair enough, thank you & apologies for lack of info. FWIW, I've spent a couple hrs trying various things that always resulted in errors, only then did I post. For more information, this is:
Firmware Version: DD-WRT v3.0-r52004 std (03/13/23)
Kernel Version: Linux 4.14.306 #3600 SMP Mon Mar 13 07:15:19 +06 2023 mips
...so yes, it should work. And if I'm understanding this correctly, if no arguments are given, ccp should negotiate one of the available schemes but it does not.
Come to think of it, I haven't yet tried "noccp" along with "deflate x,y" yet. Maybe that will help.
EDIT: Tried the above, no errors on either end of the link. However:
Well, I did some experiments and so far I've found the problem seems to be specific to ppp on dd-wrt.
First, I thought the issue was my weird radio link so I removed that and replaced it with a straight-through physical cable - same result. Then I thought it was because I'm using a very small MTU of 296, so I made that 1500 - same result ("ppp: compressor dropped pkt")
Then I replaced the entire router end (client) with a Linux computer but kept the same host hardware (Raspberry Pi, which provides the connection). I ran the exact same command that I had on dd-wrt (except that I started with an MTU of 1500) - WORKS!
Then I reduced the MTU to 296 - which breaks IPV6, but otherwise this also works.
The way I understand it is that the client (dd-wrt) offers mppe, deflate and bsd compression, but host (Raspberry Pi) can't do MPPE, so they agree to remove mppe from the choices. After that, at least one side should say "Enabled", as above.
However, they never do. The only difference I can see is the "id=02" in the working case and "id=01" in the failing case, but I can't find any docs about that.
TLDR: I think this problem is specific to dd-wrt - how could I go about debugging this?