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 From:  "Morten Winther" <freebsd at mwi dot dk>
 To:  m0n0wall at lists dot m0n0 dot ch
 Subject:  PPTP errors - patch
 Date:  Sun, 10 Oct 2004 17:34:56 +0200 (CEST)
Hello

Can someone help me with this patch. It's pretty old and the code seems to
have changed a bit in FreeBSD cvs.

--- sys/netgraph/ng_ppp.c.orig Thu Nov 21 12:39:06 2002
+++ sys/netgraph/ng_ppp.c Thu Nov 21 12:39:26 2002
@@ -744,7 +744,7 @@
  case HOOK_INDEX_VJC_VJIP:
   if (priv->conf.enableCompression
       && priv->hooks[HOOK_INDEX_COMPRESS] != NULL) {
-   if ((m = ng_ppp_addproto(m, proto, 1)) == NULL) {
+   if ((m = ng_ppp_addproto(m, proto, 0)) == NULL) {
     NG_FREE_META(meta);
     return (ENOBUFS);
    }

From google:

Looks like the other side is semi-broken. It's interpreting 0x21 0x45
as a two byte protocol ID, whereas really it's a one byte compressed
protocol ID (0x0021) followed by the first byte of an IP packet (0x45).
That's clearly broken, because only the last byte of a protocol ID can
be odd.

Perhaps it's not expecting the 0x0021 to be protocol-compressed...
the MPPE RFC (3078) is silent on whether or not that's allowed.

http://groups.google.dk/groups?hl=da&lr=&threadm=1037910248.914.8.camel_vbook%40ns.sol.net&rnum=4&prev=/groups%3Fq%3D%2522protocol%25200x2145%2520was%2520rejected%2522%26hl%3Dda%26lr%3D%26sa%3DN%26tab%3Dwg


Errors from log:

Oct 10 15:18:10 	mpd: [pt1] LCP: rec'd Protocol Reject #48 link 0 (Opened)
Oct 10 15:18:10 	mpd: [pt1] LCP: protocol 0x2145 was rejected
Oct 10 15:18:12 	mpd: [pt1] LCP: rec'd Protocol Reject #50 link 0 (Opened)
Oct 10 15:18:12 	mpd: [pt1] LCP: protocol 0x2145 was rejected
Oct 10 15:18:14 	mpd: [pt1] LCP: rec'd Protocol Reject #51 link 0 (Opened)
Oct 10 15:18:14 	mpd: [pt1] LCP: protocol 0x2145 was rejected
Oct 10 15:18:16 	mpd: [pt1] LCP: rec'd Protocol Reject #52 link 0 (Opened)
Oct 10 15:18:16 	mpd: [pt1] LCP: protocol 0x2145 was rejected
Oct 10 15:18:18 	mpd: [pt1] LCP: rec'd Protocol Reject #53 link 0 (Opened)
Oct 10 15:18:18 	mpd: [pt1] LCP: protocol 0x2145 was rejected
Oct 10 15:18:20 	mpd: [pt1] LCP: rec'd Protocol Reject #54 link 0 (Opened)
Oct 10 15:18:20 	mpd: [pt1] LCP: protocol 0x2145 was rejected

Best regards
Morten