04-12-2011
Well, if the port is bound to the Scream program, no other users can bind it. Do you want to copy the flow into Scream on every connecting service? There is a tool, tcp_relay.c, that listens on one port and for every connection, spins off a child that connects to $2 port $3 and forwards all data both ways, a sort of firewall proxy. You can monitor Scream with truss/tusc/strace as it runs and see all the system calls it does.
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LEARN ABOUT FREEBSD
tftp-proxy
TFTP-PROXY(8) BSD System Manager's Manual TFTP-PROXY(8)
NAME
tftp-proxy -- Internet Trivial File Transfer Protocol proxy
SYNOPSIS
tftp-proxy [-v] [-w transwait]
DESCRIPTION
tftp-proxy is a proxy for the Internet Trivial File Transfer Protocol invoked by the inetd(8) internet server. TFTP connections should be
redirected to the proxy using the pf(4) rdr command, after which the proxy connects to the server on behalf of the client.
The proxy establishes a pf(4) rdr rule using the anchor facility to rewrite packets between the client and the server. Once the rule is
established, tftp-proxy forwards the initial request from the client to the server to begin the transfer. After transwait seconds, the pf(4)
NAT state is assumed to have been established and the rdr rule is deleted and the program exits. Once the transfer between the client and
the server is completed, the NAT state will naturally expire.
Assuming the TFTP command request is from $client to $server, the proxy connected to the server using the $proxy source address, and $port is
negotiated, tftp-proxy adds the following rule to the anchor:
rdr proto udp from $server to $proxy port $port -> $client
The options are as follows:
-v Log the connection and request information to syslogd(8).
-w transwait
Number of seconds to wait for the data transmission to begin before removing the pf(4) rdr rule. The default is 2 seconds.
CONFIGURATION
To make use of the proxy, pf.conf(5) needs the following rules. The anchors are mandatory. Adjust the rules as needed for your configura-
tion.
In the NAT section:
nat on $ext_if from $int_if -> ($ext_if:0)
no nat on $ext_if to port tftp
rdr-anchor "tftp-proxy/*"
rdr on $int_if proto udp from $lan to any port tftp ->
127.0.0.1 port 6969
In the filter section, an anchor must be added to hold the pass rules:
anchor "tftp-proxy/*"
inetd(8) must be configured to spawn the proxy on the port that packets are being forwarded to by pf(4). An example inetd.conf(5) entry fol-
lows:
127.0.0.1:6969 dgram udp wait root
/usr/libexec/tftp-proxy tftp-proxy
SEE ALSO
tftp(1), pf(4), pf.conf(5), ftp-proxy(8), inetd(8), syslogd(8), tftpd(8)
CAVEATS
tftp-proxy chroots to /var/empty and changes to user ``proxy'' to drop privileges.
BSD
November 28, 2005 BSD