Because 127.0.0.1 is the local IP. By typing that, you are attempting to connect to yourself.

I have tried the same thing with my IP address "99.235.184.249" which are the same for the both computers. When one of the computers acts as a dedicated server, the other computer does not connect, the same messages pops out - IPX Tunneling Client failed to connect to server at IP.

99.235.184.249 is probably your internet ip address. Check out your local LAN addresses. And what operating systems are you using?

h-a-l-9000 Thank you for your answer! Me and my brother are both using Windows 7 operating systems. I searched the internet and found that the local LAN address can found via the 'ipconfig' command in the cmd.exe

Here is what is written, i hope this can be of help, because honestly, i don't understand much here... But from what i see, something is wrong with my LAN address because i don't seem to have it...

Windows IP Configuration

Wireless LAN adapter Wireless Network Connection:

Connection-specific DNS Suffix . :
Link-local IPv6 Address . . . . . : fe80::b588:3217:f497:791e%12
IPv4 Address. . . . . . . . . . . : 192.168.0.22
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Default Gateway . . . . . . . . . : 192.168.0.1

Ethernet adapter Local Area Connection:

Media State . . . . . . . . . . . : Media disconnected
Connection-specific DNS Suffix . :

Ethernet adapter Hamachi:

Connection-specific DNS Suffix . :
IPv6 Address. . . . . . . . . . . : 2620:9b::1915:77a1
Link-local IPv6 Address . . . . . : fe80::2450:420:8dcd:dca1%17
IPv4 Address. . . . . . . . . . . : 25.21.119.161
Subnet Mask . . . . . . . . . . . : 255.0.0.0
Default Gateway . . . . . . . . . : 2620:9b::1900:1
25.0.0.1

Tunnel adapter isatap.{210E119E-671B-4789-A14D-19D736DFB14D}:

Media State . . . . . . . . . . . : Media disconnected
Connection-specific DNS Suffix . :

Tunnel adapter isatap.{C26A410C-B755-49CB-A2D3-C39CFE2283FF}:

Media State . . . . . . . . . . . : Media disconnected
Connection-specific DNS Suffix . :

Tunnel adapter Teredo Tunneling Pseudo-Interface:

Connection-specific DNS Suffix . :
IPv6 Address. . . . . . . . . . . : 2001:0:9d38:6ab8:2c93:326b:9c14:4706
Link-local IPv6 Address . . . . . : fe80::2c93:326b:9c14:4706%13
Default Gateway . . . . . . . . . :

Tunnel adapter isatap.{EA23A8E2-32A1-4A09-914C-13BA7EC164B2}:

Media State . . . . . . . . . . . : Media disconnected
Connection-specific DNS Suffix . :

Tunnel adapter Reusable ISATAP Interface {D88B3D46-3994-468E-90D7-FB122D7DD3E0}:

Media State . . . . . . . . . . . : Media disconnected
Connection-specific DNS Suffix . :

Tunnel adapter 6TO4 Adapter:

Media State . . . . . . . . . . . : Media disconnected
Connection-specific DNS Suffix . :

EDIT: Oh and Hamachi doesn't work, i tried installing it but i have some router problem i think, i would really prefer to play just with the awesome DosBox without any additional programs.

192.168.0.22 is your LAN address

Thank you for your help but alas, still no luck. Same message for both IP addresses which are different. I tried starting the server from my computer and from my brothers computer, but i cannot connect - IPX Tunneling Client failed to connect to server at IP.

Hello 3L3m3nt@L,
and hello everybody trying to use the IPX-Tunneling of DosBox for playing old games,

here is my way to connect my PC's (all connected to my router via WLAN/ 1x Win7, 1x WinXP // using DosBox 0.74)

make sure that in both (all) DosBox configurations the ipx is set to true (IPX=true)

then just start on one PC the server:
"ipxnet startserver"

check your IP-adrees on the local area network (not your IP seen by the outside/internet)
a) by using the comand line: "ipconfig /all" -> see the IP-adress / IPv4 (in my example 192.168.1.125 and 192.168.1.248)
b) see your router configuration. in the WLAN overview it should sum up all PC IP-adresses conneted to it.

then connect the client to the server on the other PC(s) using the server IP-adress:
"ipxnet connect 192.168.1.125"

... see two pictures attached.

if this still doesn't work you might try to use a specified port:
e.g. "ipxnet startserver 13300", then also check/add the prot forwarding in your router configuration.
(but using DosBox to connet just PC's on one side of the router shoun't need that // maybe if your Firewall/Security options are very strict?!)

(I guess leileilol also answerd the question more compact already ... but I hope this can help you or somebody else too...)

good luck and have fun! 😀