ppp between two machines over serail without a modem

Question

Can't delete this question. It was moved to another forum.

I'm trying to setup a PPP connection between two Linux machines over a serial line. I followed these instructions but it didn't work. The two machines are Fedora 28 Linux on an Intel(R) Core(TM) i7-7600U CPU @ 2.80GHz and a custom built board with Linux 4.14.0-xilinx-v2018.2 on an ARMv7 A.

Here are the commands and the output I got on a Fedora machine:

$ sudo pppd -detach debug passive lock xonxoff 192.168.10.100:192.168.10.1 /dev/ttyUSB0 9600
[sudo] password for user:
using channel 3
Using interface ppp0
Connect: ppp0 <--> /dev/ttyUSB0
sent [LCP ConfReq id=0x1 <asyncmap 0xa0000> <magic 0x888f0bcb> <pcomp> <accomp>]
sent [LCP ConfReq id=0x1 <asyncmap 0xa0000> <magic 0x888f0bcb> <pcomp> <accomp>]
sent [LCP ConfReq id=0x1 <asyncmap 0xa0000> <magic 0x888f0bcb> <pcomp> <accomp>]
sent [LCP ConfReq id=0x1 <asyncmap 0xa0000> <magic 0x888f0bcb> <pcomp> <accomp>]
sent [LCP ConfReq id=0x1 <asyncmap 0xa0000> <magic 0x888f0bcb> <pcomp> <accomp>]
sent [LCP ConfReq id=0x1 <asyncmap 0xa0000> <magic 0x888f0bcb> <pcomp> <accomp>]
sent [LCP ConfReq id=0x1 <asyncmap 0xa0000> <magic 0x888f0bcb> <pcomp> <accomp>]
sent [LCP ConfReq id=0x1 <asyncmap 0xa0000> <magic 0x888f0bcb> <pcomp> <accomp>]
sent [LCP ConfReq id=0x1 <asyncmap 0xa0000> <magic 0x888f0bcb> <pcomp> <accomp>]
sent [LCP ConfReq id=0x1 <asyncmap 0xa0000> <magic 0x888f0bcb> <pcomp> <accomp>]
LCP: timeout sending Config-Requests

And here are the commands and output I got Linux 4.14.0-xilinx-v2018.2

root@cpe-08:/data# pppd -detach debug passive lock xonxoff 192.168.10.1:192.168.10.100 /dev/ttyS0 9
600

Yep, you saw it correctly, there was no other output Linux4.14.0-xilinx-v2018.2.

I was expecting to see ppp0 interface on both machines but didn't see any of them.

Here is the output of ifconfig on Fedora 28 after running pppd command

$ ifconfig
enp0s20f0u2u2: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 172.24.176.116  netmask 255.255.255.0  broadcast 172.24.176.255
        inet6 fe80::63fd:53b6:8b94:1abf  prefixlen 64  scopeid 0x20<link>
        ether 00:0e:c6:a5:94:88  txqueuelen 1000  (Ethernet)
        RX packets 5016  bytes 457454 (446.7 KiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 1368  bytes 141981 (138.6 KiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

enp0s31f6: flags=4099<UP,BROADCAST,MULTICAST>  mtu 1500
        ether 54:e1:ad:8c:32:a5  txqueuelen 1000  (Ethernet)
        RX packets 0  bytes 0 (0.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 0  bytes 0 (0.0 B)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
        device interrupt 16  memory 0xec200000-ec220000

lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536
        inet 127.0.0.1  netmask 255.0.0.0
        inet6 ::1  prefixlen 128  scopeid 0x10<host>
        loop  txqueuelen 1000  (Local Loopback)
        RX packets 184264  bytes 109696260 (104.6 MiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 184264  bytes 109696260 (104.6 MiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

virbr0: flags=4099<UP,BROADCAST,MULTICAST>  mtu 1500
        inet 192.168.122.1  netmask 255.255.255.0  broadcast 192.168.122.255
        ether 52:54:00:62:c0:6c  txqueuelen 1000  (Ethernet)
        RX packets 0  bytes 0 (0.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 0  bytes 0 (0.0 B)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

wlp58s0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 100.96.37.134  netmask 255.255.255.192  broadcast 100.96.37.191
        inet6 fe80::3728:7f03:ba95:5757  prefixlen 64  scopeid 0x20<link>
        inet6 2620:10d:c0be:2226:7261:932:1670:38bb  prefixlen 64  scopeid 0x0<global>
        ether f8:34:41:af:1a:0e  txqueuelen 1000  (Ethernet)
        RX packets 13305344  bytes 16391874252 (15.2 GiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 5691206  bytes 1228184162 (1.1 GiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

And here is the output from ifconfig on a Linux 4.14.0-xilinx-v2018.2 after running a pppd command

# ifconfig
eth0      Link encap:Ethernet  HWaddr 00:04:35:00:01:08
          inet addr:172.24.176.208  Bcast:172.24.176.255  Mask:255.255.255.0
          inet6 addr: fe80::204:35ff:fe00:108/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:2515 errors:0 dropped:0 overruns:0 frame:0
          TX packets:753 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:221227 (216.0 KiB)  TX bytes:93698 (91.5 KiB)
          Interrupt:27 Base address:0xb000

lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:36160 errors:0 dropped:0 overruns:0 frame:0
          TX packets:36160 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:1516794 (1.4 MiB)  TX bytes:1516794 (1.4 MiB)

I know that Linux 4.14.0-xilinx-v2018.2 was compiled to include ppp support. I would have included an excerpt from a '.config' but it is not provided with the build. The reason I know that ppp support is in the kernel is because I asked our build guy and he said he included it. I would appreciate any help on this.

Answer 1

After messing around for sometime I managed to get it working. Here is the command for Fedora machine

sudo 0pppd -detach local debug noauth passive lock 192.168.10.100:192.168.10.1 /dev/ttyUSB0 9600

And here is the command for a Linux 4.14.0-xilinx-v2018.2 machine

pppd -detach persist debug local noauth passive lock 192.168.10.1:192.168.10.100 /dev/ttyS0 9600

I've been struggling with the problem for the past 2 months. Not sure why this question was initially downgraded. I imagine there are other people who had the same issue.