ftp problems with ipchain

ftp problems with ipchain

Post by Roy Limle » Wed, 27 Jan 1999 04:00:00

Hi all,

I've setup my linux kernel as a router with ipmasq option selected.
Then I tried to do
an ftp from Subnet A to Subnet B:

        [Subnet A]  <---->  [Linux as a router with ipmasq]   <----->
[Subnet B]

Anonymous ftp can work fine, but non-anonymous ftp doesn't.  On Subnet
B's machine,
I did "netstat -a | grep ftp" and it only give me one port link.
However, if I try to ftp to
subnet B from other machine without going through the Linux router, I
get 2 ports link.

I have a feeling somehow that ipmasq denying the information to come
back from
B to A.  Has anyone had this problem before and found a solution?

Thanks in advance,


1. "Indirect FTP" through IPChains problem?

This was one of those little surprises in Ziegler's book called "Linux
Firewalls".  Unbeknown to me there is a "passive ftp" used by browsers.

Here's my iptables entry to enable that.  It was taken from that book
and adapted to iptables.

# Passive mode FTP data channels (used by web browsers)
iptables -A INPUT -i $EXTERNAL_INTERFACE -p tcp ! --syn -s $ANYWHERE --source-port $UNPRIVPORTS -d $IPADDR \
        --destination-port $UNPRIVPORTS -j ACCEPT
iptables -A OUTPUT -o $EXTERNAL_INTERFACE -p tcp -s $IPADDR --source-port $UNPRIVPORTS -d $ANYWHERE \
        --destination-port $UNPRIVPORTS -j ACCEPT


It is, in fact, a sendmail alias; the digit 'N' is incremented regularly.
Spammed aliases will be deleted.  Currently, mike[25,26]
are valid.  If email to mikeN bounces, try mikeN+1.

2. The Musician...

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