PLIP sends packets but does not work under RH 6.1

PLIP sends packets but does not work under RH 6.1

Post by Sebastiano Vign » Mon, 27 Dec 1999 04:00:00



I have spent a week-end trying to get plip to work between two out-of-the-box
RedHat 6.1 Linuxes, with no results. The surprising thing that happens is that
the link works: when I ping one machine (urfida) from the other (dina) the
packets _are_ sent, as tcpdump (on urfida) shows:

23:20:02.038498 plip0 P dina > urfida: icmp: echo request
23:20:03.038278 plip0 P dina > urfida: icmp: echo request
23:20:04.038117 plip0 P dina > urfida: icmp: echo request
23:20:05.038030 plip0 P dina > urfida: icmp: echo request
23:20:06.037867 plip0 P dina > urfida: icmp: echo request
23:20:07.037755 plip0 P dina > urfida: icmp: echo request
23:20:08.037610 plip0 P dina > urfida: icmp: echo request

But--surprise!--the back packet is never sent. It is like inetd is not
seeing the packets, even if they get to the machine.

I have sincerely no idea of what's happening. Of course all the parallel
problems are ruled out, as packets travel happily in both direction without
errors. But the networking system does not see them.

I enclose at the end of the message the ifconfig/route output for both
machines, and the complete description of a ping packet as made by ethereal.
Note that I have even tried to run plip in PROMISC mode and/or activate a
default route through the link for all packets, with no results.

The only "suspicious" thing is that to/from Ethernet addresses of the packets
are the same, but if this is the problem I think it is a bug in plip.c
(which dates 1997...).

Thank you for any help,

                                        seba

----------- urfida -----------------
lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          UP LOOPBACK RUNNING  MTU:3924  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0

plip0     Link encap:Ethernet  HWaddr FC:FC:C0:A8:01:01  
          inet addr:192.168.1.1  P-t-P:192.168.1.2  Mask:255.255.255.255
          UP POINTOPOINT RUNNING NOARP MTU:1500  Metric:1
          RX packets:57 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:10
          Interrupt:5 Base address:0x278

Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
192.168.1.2     *               255.255.255.255 UH    0      0        0 plip0
127.0.0.0       *               255.0.0.0       U     0      0        0 lo

---------- dina -------------------
lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          UP LOOPBACK RUNNING  MTU:3924  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0

plip0     Link encap:Ethernet  HWaddr FC:FC:C0:A8:01:02  
          inet addr:192.168.1.2  P-t-P:192.168.1.1  Mask:255.255.255.255
          UP POINTOPOINT RUNNING NOARP  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:10
          Interrupt:7 Base address:0x378

Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
192.168.1.1     *               255.255.255.255 UH    0      0        0 plip0
127.0.0.0       *               255.0.0.0       U     0      0        0 lo
--------------------------------------
Frame 1:
Frame (98 on wire, 98 captured)
    Arrival Time: Dec 19, 1999 23:20:36.0339
    Packet Length: 98 bytes
    Capture Length: 98 bytes
Ethernet II
    Destination: fc:fc:c0:a8:01:02 (fc:fc:c0:a8:01:02)
    Source: fc:fc:c0:a8:01:02 (fc:fc:c0:a8:01:02)
    Type: IP (0x0800)
Internet Protocol
    Version: 4
    Header length: 20 bytes
    Type of service: 0x00 (None)
        000. .... = routine precedence
        ...0 .... = normal delay
        .... 0... = normal throughput
        .... .0.. = normal reliability
        .... ..0. = normal cost
    Total Length: 84
    Identification: 0x0061
    Flags: 0x0
        .0.. .... = may fragment
        ..0. .... = last fragment
    Fragment offset: 0
    Time to live: 64
    Protocol: ICMP
    Header checksum: 0xf6f4
    Source: dina (192.168.1.2)
    Destination: urfida (192.168.1.1)
Internet Control Message Protocol
    Type: 8 (Echo (ping) request)
    Code: 0
    Checksum: 0x6a05
    Identifier: 0xb801
    Sequence number: 24832
    Data (56 bytes)

   0  7e59 5d38 0bff 0700 0809 0a0b 0c0d 0e0f   ~Y]8............
  10  1011 1213 1415 1617 1819 1a1b 1c1d 1e1f   ................
  20  2021 2223 2425 2627 2829 2a2b 2c2d 2e2f    !"#$%&'()*+,-./
  30  3031 3233 3435 3637                       01234567