transparent TCP proxy. простейший редирект трафика порта.

~# ifconfig


lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

venet0    Link encap:UNSPEC  HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00
          inet addr:127.0.0.2  P-t-P:127.0.0.2  Bcast:0.0.0.0  Mask:255.255.255.255
          UP BROADCAST POINTOPOINT RUNNING NOARP  MTU:1500  Metric:1
          RX packets:6433 errors:0 dropped:0 overruns:0 frame:0
          TX packets:5702 errors:0 dropped:28 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:445424 (434.9 KiB)  TX bytes:663221 (647.6 KiB)

venet0:0  Link encap:UNSPEC  HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00
          inet addr:11.11.11.11  P-t-P:11.11.11.11  Bcast:11.11.11.11  Mask:255.255.255.255
          UP BROADCAST POINTOPOINT RUNNING NOARP  MTU:1500  Metric:1

~# echo "1" > /proc/sys/net/ipv4/ip_forward
~# iptables -t nat -A POSTROUTING -o venet0:0 -j MASQUERADE
~# iptables -t nat -A PREROUTING -p tcp  --dport 8080  -j DNAT --to-destination 195.27.31.252:80
~# iptables -t nat -A PREROUTING -p udp  --dport 8080  -j DNAT --to-destination 195.27.31.252:80
~# route add -host 195.27.31.252  dev venet0:0

~# route

Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
195.27.31.252    *               255.255.255.255 UH    0      0        0 venet0
default         *               0.0.0.0         U     0      0        0 venet0

~# iptables-save

# Generated by iptables-save v1.4.21 on Wed Jun  5 00:13:51 2019
*nat
:PREROUTING ACCEPT [182:8756]
:POSTROUTING ACCEPT [1:71]
:OUTPUT ACCEPT [1:71]
-A PREROUTING -p tcp -m tcp --dport 8080 -j DNAT --to-destination 195.27.31.252:80
-A PREROUTING -p udp -m udp --dport 8080 -j DNAT --to-destination 195.27.31.252:80
-A POSTROUTING -o venet0:0 -j MASQUERADE
COMMIT
# Completed on Wed Jun  5 00:13:51 2019
# Generated by iptables-save v1.4.21 on Wed Jun  5 00:13:51 2019
*filter
:INPUT ACCEPT [1362:140055]
:FORWARD ACCEPT [1:52]
:OUTPUT ACCEPT [1279:178686]
COMMIT
# Completed on Wed Jun  5 00:13:51 2019
# Generated by iptables-save v1.4.21 on Wed Jun  5 00:13:51 2019
*mangle
:PREROUTING ACCEPT [1363:140107]
:INPUT ACCEPT [1362:140055]
:FORWARD ACCEPT [1:52]
:OUTPUT ACCEPT [1280:178766]
:POSTROUTING ACCEPT [1280:178738]
COMMIT
# Completed on Wed Jun  5 00:13:51 2019
# Generated by iptables-save v1.4.21 on Wed Jun  5 00:13:51 2019
*raw
:PREROUTING ACCEPT [1363:140107]
:OUTPUT ACCEPT [1280:178766]
COMMIT
# Completed on Wed Jun  5 00:13:51 2019