Add a strong recomendation to set net.inet.tcp.mss_ifmtu=1 when using

pppoe interface to connect to the internet.

share/man/man4/pppoe.4

@@ -1,4 +1,4 @@
-.\"	$NetBSD: pppoe.4,v 1.3 2001/12/18 13:33:18 ad Exp $
+.\"	$NetBSD: pppoe.4,v 1.4 2002/01/13 18:40:52 martin Exp $
 .\"
 .\" Copyright (c) 2001 Martin Husemann. All rights reserved.
 .\"
@@ -84,6 +84,32 @@ on the available options see
 This all is typically accomplished using an
 .Pa /etc/ifconfig.pppoe0
 file.
+.Sh IMPORTANT NOTE
+If you are using a
+.Nm
+interface, you will have an unusual low MTU for todays internet.
+Combined with a lot of misconfigured sites (host using path MTU discovery 
+behind a router blocking all ICMP traffic) this will often cause problems.
+Connections to this servers will only work, if your system advertizes the
+right MSS in the tcp three way handshake. To get the right MSS, you need
+to set
+.Bd -literal
+# Obey interface MTUs when calculationg MSS
+net.inet.tcp.mss_ifmtu=1
+.Ed
+
+in your
+.Pa /etc/sysctl.conf
+file.
+This causes the calculated MSS to be based on the MTU of the interface
+via which the packet is send. This is always the right value if you are
+sure the answer to this packet will be received on the same interface
+(I.e. you only have one interface connected to the internet.)
+.Pp
+Unfortunately this sysctl does not fix the MSS advertized by hosts in
+the network behind a
+.Nm
+connected router.
 .Sh EXAMPLES
 A typical
 .Pa /etc/ifconfig.pppoe0