Port forwarding using netcat (nc)

netcat_port_forwarding.md

Network setup

10.1.1.4/24 --> a system connected to bmc system. 10.1.1.5/24 --> bmc system. localhost --> my laptop. Suppose we want to access a service running at UDP port 623 but UDP port 623 is blocked by our firewall and TCP port 80 is unblocked. So we can use nc to create a tunnel using TCP port 80.

Configuration

1. laptop terminal#1:
   • mkfifo /tmp/fifo
   • sudo nc -l -u -p 623 < /tmp/fifo | nc 10.1.1.4 80 > /tmp/fifo
2. Proxy system (10.1.1.4/24) ternminal:
   • mkfifo /tmp/fifo
   • sudo nc -l -p 80 < /tmp/fifo | nc -u 10.1.1.5 623 > /tmp/fifo

Using the tunnel

1. laptop terminal#2:
   • ipmitool -C 17 -I lanplus -H localhost -p 623 -U username -P password lan print

    Set in Progress         : Set Complete
    Auth Type Support       :
    Auth Type Enable        : Callback :
                            : User     :
                            : Operator :
                            : Admin    :
                            : OEM      :
    IP Address Source       : Static Address
    IP Address              : 10.1.1.5
    Subnet Mask             : 255.255.255.0
    MAC Address             : ff:ee:dd:cc:bb:aa
    Default Gateway IP      : 10.1.1.1
    Default Gateway MAC     : 00:00:00:00:00:00
    802.1q VLAN ID          : Disabled
    RMCP+ Cipher Suites     : 17
    Cipher Suite Priv Max   : aaaaaaaaaaaaaaa
                            :     X=Cipher Suite Unused
                            :     c=CALLBACK
                            :     u=USER
                            :     o=OPERATOR
                            :     a=ADMIN
                            :     O=OEM
    Bad Password Threshold  : Not Available
   

Note: We are using local IP address

netcat_reference.md

https://en.wikipedia.org/wiki/Netcat#Proxying http://zarb.org/~gc/html/udp-in-ssh-tunneling.html https://www.tecmint.com/netcat-nc-command-examples/

• Listen on a tcp port:

  • nc -l -p 80

• Listen on an UDP port:

  • nc -l -u -p 623

• Read from a remote TCP port:

  • nc 10.1.1.4 80

• Write to a remote TCP port:

  • echo "some message" | nc 10.1.1.4 80

• Read from a remote UDP port:

  • nc -u 10.1.1.4 80

• Write to a remote UDP port:

  • echo "some message" | nc -u 15.115.65.34 80

• Chat program:

  • Server:
    • nc -l -vv -p 5000
  • Client:
    • nc localhost 5000

• Scan remote port (e.g 22):

  • nc -v -w 2 -z 10.1.1.4 22