500 lines
9.7 KiB
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500 lines
9.7 KiB
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<HTML
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>How does it work?</TITLE
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>Remote Bridging with IP Tunnels mini-HOWTO</TH
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CLASS="SECT1"
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><H1
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CLASS="SECT1"
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><A
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NAME="AEN19">1. How does it work?</H1
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><P
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>You can transparently bridge traffic between 2 ethernet LANs to unite them, if both of them are connected to Internet.</P
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><P
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>There is no way to do a <SPAN
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CLASS="QUOTE"
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>"real"</SPAN
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> bridge, you can only bridge third level protocols, which linux knows how to route, but ethernet traffic with those protocols will seem bridged. You can make 2 ethernet bridges, to bridge IP and/or IPX traffic. You cannot transparently bridge any other third level protocols between distinct LANs. You should read the rest of this document to determine whether you can bridge any other protocol.</P
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><DIV
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CLASS="SECT2"
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><H2
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CLASS="SECT2"
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><A
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NAME="AEN24">1.1. Bridging IP over ethernet traffic between 2 LANs.</H2
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><P
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>If you have:
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<TABLE
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COLOR="#000000"
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><PRE
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CLASS="SCREEN"
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>PC1 (192.168.0.1 /24)--|
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PC3 (192.168.0.3 /24)--|
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PC5 (192.168.0.5 /24)--|--[ eth0 - bridge_1 - eth1 (195.0.0.1) ]
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PC253 (192.168.0.253/24)--|
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| (192.168.0.2 /24) PC2
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| (192.168.0.4 /24) PC4
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[ (192.0.0.1) eth1 - bridge_2 - eth0 ] --| (192.168.0.6 /24) PC6
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| (192.168.0.254/24) PC254</PRE
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></FONT
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></TD
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></TABLE
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></P
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><P
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><I
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CLASS="MEDIALABEL"
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>bridge_1</I
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> and <I
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CLASS="MEDIALABEL"
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>bridge_2</I
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> are your Linux bridges and externally connected to the Internet interface eth1. So <TT
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CLASS="USERINPUT"
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><B
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>195.0.0.1</B
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></TT
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> and <TT
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CLASS="USERINPUT"
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><B
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>192.0.0.1</B
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></TT
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> can be any valid Internet addresses given to you by your ISP.</P
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><P
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>So, you should:</P
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><P
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></P
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><OL
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TYPE="1"
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><LI
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><P
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>Get two linux computers with kernels 2.2 or 2.4. Kernels should be compiled with <SPAN
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CLASS="ACRONYM"
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>PPP</SPAN
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> and <SPAN
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CLASS="APPLICATION"
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>Advanced Router</SPAN
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>. You also need the <SPAN
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CLASS="APPLICATION"
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>iproute2</SPAN
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> package properly installed. Information on <SPAN
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CLASS="APPLICATION"
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>iproute2</SPAN
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> can be found in <TT
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CLASS="FILENAME"
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>Configure.help</TT
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> of your kernel in the comments under <SPAN
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CLASS="APPLICATION"
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>Advanced Router</SPAN
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>. You also need the following utilities:</P
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><P
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></P
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><UL
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><LI
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><P
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><SPAN
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CLASS="APPLICATION"
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>pppd</SPAN
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> (PPP daemon) - <A
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HREF="ftp://cs.anu.edu.au/pub/software/ppp/"
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TARGET="_top"
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>ftp://cs.anu.edu.au/pub/software/ppp/</A
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></P
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></LI
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><LI
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><P
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><SPAN
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CLASS="APPLICATION"
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>PopTop</SPAN
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> (PPTP server) - <A
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HREF="http://poptop.lineo.com/"
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TARGET="_top"
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>http://poptop.lineo.com</A
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></P
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></LI
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><LI
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><P
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><SPAN
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CLASS="APPLICATION"
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>PPTP</SPAN
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> (Linux PPTP Client, by C.S. Ananian) - <A
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HREF="http://www.pdos.lcs.mit.edu/~cananian/Projects/PPTP/"
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TARGET="_top"
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>http://www.pdos.lcs.mit.edu/~cananian/Projects/PPTP/</A
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></P
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></LI
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><LI
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><P
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><SPAN
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CLASS="APPLICATION"
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>tarpd</SPAN
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> (a trivial proxy arp daemon) - <A
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HREF="http://www.cs.hut.fi/~tricky/utils/net/tarpd-1.6.tar.gz"
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TARGET="_top"
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>htp://www.cs.hut.fi/~tricky/utils/net/tarpd-1.6.tar.gz</A
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></P
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></LI
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></UL
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><P
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>You can also find them on <A
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HREF="http://www.freshmeat.net"
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TARGET="_top"
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>http://www.freshmeat.net</A
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></P
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><P
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>Please, keep in mind that you need special patches for pppd and the kernel if you want to do <SPAN
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CLASS="APPLICATION"
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>MS Chap</SPAN
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> and <SPAN
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CLASS="APPLICATION"
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>MS Encryption (MPPE)</SPAN
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>. Refer to the <SPAN
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CLASS="APPLICATION"
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>PoPTop</SPAN
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> manual for instructions on how to get and install these patches.</P
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></LI
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><LI
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><P
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>Connect your routers to Internet, or establish any other communication between them with the exception of IP.</P
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></LI
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><LI
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><P
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>Make a <SPAN
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CLASS="ACRONYM"
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>PPTP</SPAN
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> tunnel between them. There are example configurations in the PoPToP (server) and pptp (client) manuals.</P
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></LI
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><LI
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><P
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>Now you should have two bridges and an IP tunnel between then, possibly encrypted (refer to the <SPAN
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CLASS="ACRONYM"
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>PPP</SPAN
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> manual). Let's configure bridging.</P
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></LI
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><LI
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><P
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>Remember that the bridge is really a router, so we need to run the following commands on our bridges (this assumes <I
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CLASS="MEDIALABEL"
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>bridge_1</I
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> and <I
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CLASS="MEDIALABEL"
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>bridge_2</I
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> are IP addresses, assigned to each end of the <SPAN
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CLASS="ACRONYM"
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>PPTP</SPAN
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> tunnel between bridges):</P
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><TABLE
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BORDER="1"
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BGCOLOR="#E0E0E0"
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WIDTH="90%"
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><TR
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><TD
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><FONT
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COLOR="#000000"
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><PRE
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CLASS="SCREEN"
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> bridge_1$ip route add 192.168.0.2 via bridge_2
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bridge_1$ip route add 192.168.0.4 via bridge_2
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bridge_1$ip route add 192.168.0.6 via bridge_2
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bridge_1$ip route add 192.168.0.254 via bridge_2
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bridge_1$ip route add 192.168.0.255 via bridge_2
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</PRE
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></FONT
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></TD
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></TR
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></TABLE
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><P
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>On the other side:</P
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><TABLE
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BORDER="1"
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BGCOLOR="#E0E0E0"
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WIDTH="90%"
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><TR
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><TD
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><FONT
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COLOR="#000000"
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><PRE
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CLASS="SCREEN"
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> bridge_2$ip route add 192.168.0.1 via bridge_1
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bridge_2$ip route add 192.168.0.3 via bridge_1
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bridge_2$ip route add 192.168.0.5 via bridge_1
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bridge_2$ip route add 192.168.0.253 via bridge_1
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</PRE
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></FONT
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></TD
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></TR
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></TABLE
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><P
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>This will tell each of bridges which hosts are on the other side. You can do the same with the old-style <TT
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CLASS="USERINPUT"
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><B
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>route</B
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></TT
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> command. It will look like:</P
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><TABLE
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BORDER="1"
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BGCOLOR="#E0E0E0"
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WIDTH="90%"
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><TR
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><TD
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><FONT
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COLOR="#000000"
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><PRE
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CLASS="SCREEN"
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> bridge_1$route add -host 192.168.0.2 gw bridge_2
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bridge_1$route add -host 192.168.0.4 gw bridge_2
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bridge_1$route add -host 192.168.0.6 gw bridge_2
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bridge_1$route add -host 192.168.0.254 gw bridge_2
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bridge_1$route add -host 192.168.0.255 gw bridge_2
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</PRE
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></FONT
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></TD
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></TR
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></TABLE
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><P
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>On the other side:</P
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><TABLE
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BORDER="1"
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BGCOLOR="#E0E0E0"
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WIDTH="90%"
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><TR
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><TD
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><FONT
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COLOR="#000000"
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><PRE
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CLASS="SCREEN"
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> bridge_2$route add -host 192.168.0.1 gw bridge_1
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bridge_2$route add -host 192.168.0.3 gw bridge_1
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bridge_2$route add -host 192.168.0.5 gw bridge_1
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bridge_2$route add -host 192.168.0.253 gw bridge_1
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</PRE
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></FONT
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></TD
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></TR
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></TABLE
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><P
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>Please note once more that <I
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CLASS="MEDIALABEL"
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>bridge_1</I
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> and <I
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CLASS="MEDIALABEL"
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>bridge_2</I
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> are <EM
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>not</EM
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> IP addresses given by your ISP, but IP addresses which <EM
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>you</EM
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> assigned to each end of the <SPAN
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CLASS="ACRONYM"
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>PPTP</SPAN
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> tunnel.</P
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></LI
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><LI
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><P
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>Now you have two bridges and each of them knows where to find a particular IP. But how do you tell those computers to send their traffic for the remote network to the local bridge? You need tarpd.</P
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><P
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><TT
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CLASS="USERINPUT"
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><B
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>tarpd</B
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></TT
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> is a very simple daemon, which replies to arp requests for certain IP addresses. You only need to run a <TT
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CLASS="USERINPUT"
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><B
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>tarpd</B
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></TT
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> on each bridge, and specify the list of IP addresses found on the remote end.</P
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><P
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>For example, for those two bridges you should run:</P
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><TABLE
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BORDER="1"
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BGCOLOR="#E0E0E0"
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WIDTH="90%"
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><TR
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><TD
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><FONT
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COLOR="#000000"
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><PRE
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CLASS="SCREEN"
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> bridge_1$tarpd eth0 192.168.0.2 255.255.255.255 \
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192.168.0.4 255.255.255.255 \
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192.168.0.254 255.255.255.255
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</PRE
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></FONT
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></TD
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></TR
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></TABLE
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><P
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>On the other side:</P
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><TABLE
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BORDER="1"
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BGCOLOR="#E0E0E0"
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WIDTH="90%"
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><TR
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><TD
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><FONT
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COLOR="#000000"
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><PRE
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CLASS="SCREEN"
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> bridge_2$tarpd eth0 192.168.0.1 255.255.255.255 \
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192.168.0.3 255.255.255.255 \
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192.168.0.253 255.255.255.255
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</PRE
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></FONT
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></TD
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></TR
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></TABLE
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><P
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>You specify 128 remote pairs (IP/mask. Mask should be 255.255.255.255 in order not to confuse tarpd!) on each bridge.</P
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></LI
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><LI
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><P
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>Enjoy your bridges!</P
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></LI
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></OL
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><H2
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><A
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NAME="AEN105">1.2. What about other protocols?</H2
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><P
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>Really, I can say nothing about other protocol routing. I never used them. But I suppose if you are familiar with other protocols, it should not be too difficult to bridge it this way.</P
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