PPP allows ICMP, drops TCP & UDP (not ipfw prob)

PPP allows ICMP, drops TCP & UDP (not ipfw prob)

Post by Michael Fu » Sun, 13 Jul 1997 04:00:00



FreeBSD 2.2-STABLE
Kernel PPP (pppd 2.2.0)

ipfw config:
    00100 allow ip from any to any
    65535 deny ip from any to any

Scenarios:

1.  ISP 1: PPP works like a champ.  ICMP, TCP, and UDP traffic works
    fine.

2.  ISP 2: Same PPP config -- only difference is phone # and password
    in chat file.

    * ICMP works fine -- can ping ISP and ISP can ping me; tcpdump
      run on both sides shows the ICMP echo request & reply packets.

    * TCP from ISP reaches me:  tcpdump on my side shows the SYN
      segment arriving.

    * TCP from me to ISP fails:  tcpdump on my side shows RST going
      back to ISP (nothing listening on that port); tcpdump at ISP
      never sees the RST, and ISP continues sending SYN segments.

    * UDP queries go unanswered:  tcpdump on my side shows UDP packets
      going out, but tcpdump at ISP shows nothing.

    * "ipfw show" shows increases on the allow counter.  Implicit
      deny counter remains 0.

    * ISP's other customers having no problems.

The PPP connection to ISP 2 comes up and the routes are set correctly,
as shown by the fact that I can ping them and receive the replies.  But
TCP and UDP get dropped somewhere between me and them, apparently not
by my packet filters.  The ISP's other customers have no problems (most
probably running Win95, not FreeBSD).  The identical config works fine
with ISP 1.

Any ideas?

--
Michael Fuhr
http://www.dimensional.com/~mfuhr/

 
 
 

PPP allows ICMP, drops TCP & UDP (not ipfw prob)

Post by Michael Fu » Sun, 13 Jul 1997 04:00:00



>     * TCP from me to ISP fails:  tcpdump on my side shows RST going
>       back to ISP (nothing listening on that port); tcpdump at ISP
>       never sees the RST, and ISP continues sending SYN segments.

I forgot to mention that all TCP segments I send are dropped.  If
I initiate a connection, the ISP never sees the SYN segments from my
machine.  Tcpdump at my end shows them on the interface, but tcpdump
at the ISP shows nothing.

Also, attempts to bring up PPP with this ISP often fail with the error
"IPCP: timeout sending Config-Requests".  Turning on pppd debugging
shows the following messages repeating until pppd gives up:

    rcvd [IPCP ConfReq id=0x3 <addr 204.227.16.65>]
    sent [IPCP ConfAck id=0x3 <addr 204.227.16.65>]
    sent [IPCP ConfReq id=0x1 <addr 0.0.0.0>]
    rcvd [IPCP ConfReq id=0x4 <addr 204.227.16.65>]
    sent [IPCP ConfAck id=0x4 <addr 204.227.16.65>]
    sent [IPCP ConfReq id=0x1 <addr 0.0.0.0>]
    ...

I never see this behavior with another ISP, yet this one says his other
users don't have any problems (I know the ISP and have no reason to
doubt him).

I'm trying various pppd options to see if I can find something that
works, but I'd appreciate any suggestions as to what might be wrong.

--
Michael Fuhr
http://www.dimensional.com/~mfuhr/

 
 
 

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