<HTML ><HEAD ><TITLE >Rules On Bridging</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.63 "><LINK REL="HOME" TITLE="Linux BRIDGE-STP-HOWTO" HREF="index.html"><LINK REL="PREVIOUS" TITLE="What Is A Bridge?" HREF="what-is-a-bridge.html"><LINK REL="NEXT" TITLE="Preparing The Bridge" HREF="preparing-the-bridge.html"></HEAD ><BODY CLASS="SECT1" BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#0000FF" VLINK="#840084" ALINK="#0000FF" ><DIV CLASS="NAVHEADER" ><TABLE WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="3" ALIGN="center" >Linux BRIDGE-STP-HOWTO: About The Linux Modular Bridge And STP</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="bottom" ><A HREF="what-is-a-bridge.html" >Prev</A ></TD ><TD WIDTH="80%" ALIGN="center" VALIGN="bottom" ></TD ><TD WIDTH="10%" ALIGN="right" VALIGN="bottom" ><A HREF="preparing-the-bridge.html" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="SECT1" ><H1 CLASS="SECT1" ><A NAME="RULES-ON-BRIDGING" >4. Rules On Bridging</A ></H1 ><P >There is a number of rules you are not allowed to break (otherwise your bridge will do). </P ><P ></P ><UL COMPACT="COMPACT" ><LI ><P >A port can only be a member of one bridge. </P ></LI ><LI ><P >A bridge knows nothing about routes. </P ></LI ><LI ><P >A bridge knows nothing about higher protocols than <SPAN CLASS="ACRONYM" >ARP</SPAN >. That's the reason why it can bridge any possible protocol possibly running on your Ethernet. </P ></LI ><LI ><P >No matter how many ports you have in your logical bridge, it's covered by only one logical interface </P ></LI ><LI ><P >As soon as a port (e.g. a NIC) is added to a bridge you have no more direct control about it. </P ></LI ></UL ><DIV CLASS="WARNING" ><P ></P ><TABLE CLASS="WARNING" BORDER="1" WIDTH="100%" ><TR ><TD ALIGN="CENTER" ><B >Warning</B ></TD ></TR ><TR ><TD ALIGN="LEFT" ><P >If one of the points mentioned above is not clear to you now, don't continue reading. Read the documents listed in <A HREF="recommended-reading.html" >Appendix B</A > first. </P ></TD ></TR ></TABLE ></DIV ><P >If you ever tried to ping an unmanaged switch, you will know that it doesn't work, because you don't have a IP-address for it. To switch datagrams it doesn't need one. The other thing is if you want to manage the switch. It's too much strain, to take a dumb terminal, walk to the place you installed it (normally a dark, dusty and warm room, with a lot of green and red Christmas lights), to connect the terminal and to change the settings. </P ><P >What you want is remote management, usually by SNMP, telnet, rlogin or (best) ssh. For all this services you will need a IP. That's the exception to the transparency. The new code allows you without any problem to assign a IP address to the virtual interface formed by the bridge-instance you will create in <A HREF="set-up-the-bridge.html#BASIC-SETUP" >Section 6.2</A >. All NIC's (or other interfaces) in your bridge will happily listen and respond to datagrams destined to this IP. </P ><P >All other data will not interfere with the bridge. The bridge just acts like a switch. </P ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="what-is-a-bridge.html" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="index.html" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="preparing-the-bridge.html" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >What Is A Bridge?</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" > </TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >Preparing The Bridge</TD ></TR ></TABLE ></DIV ></BODY ></HTML >