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-Bridging mini-HOWTO
-!!!Bridging mini-HOWTO
-!Christopher Cole
-
- cole@coledd.com
-
-
-
-
-March 2001
-
-
-__Revision History__Revision 1.222002-05-20Revised by: tabConverted to Docbook 4.1 SGML and added GFDL per Christopher !ColeRevision 1.212001-03-07Revised by: cc
-
-
-
-
-
-This document describes how to setup an ethernet bridge. What
-is an ethernet bridge? An ethernet bridge is a device that controls data
-packets within a subnet in an attempt to cut down the amount of traffic.
-A bridge is usually placed between two separate groups of computers that
-talk within themselves, but not so much with the computers in the other
-group. A good example of this is to consider a cluster of Macintoshes and
-a cluster of unix machines. Both of these groups of machines tend to be
-quite chatty amongst themselves, and the traffic they produce on the
-network causes collisions for the other machines who are trying to speak
-to one another. A bridge would be placed between these groups of
-computers. The job of the bridge is then to examine the destination of
-the data packets one at a time and decide whether or not to pass the
-packets to the other side of the ethernet segment. The result is a
-faster, quieter network with less collisions.
-
-
-
-
-
-----; __Table of Contents__; 1. Setup; 2. Common Problems; 3. Copyright: ; 3.1. GNU Free Documentation License; 3.2. PREAMBLE; 3.3. APPLICABILITY AND DEFINITIONS; 3.4. VERBATIM COPYING; 3.5. COPYING IN QUANTITY; 3.6. MODIFICATIONS; 3.7. COMBINING DOCUMENTS; 3.8. COLLECTIONS OF DOCUMENTS; 3.9. AGGREGATION WITH INDEPENDENT WORKS; 3.10. TRANSLATION; 3.11. TERMINATION; 3.12. FUTURE REVISIONS OF THIS LICENSE; 3.13. How to use this License for your documents
-!!!1. Setup
-
-
-
-
-
-
-*
-
-Get Bridge Config:
- BRCFG.tgz
-
-
-
-*
-*
-
-BRCFG may also be found at:
- http://coledd.com/networking/bridge
-
-
-
-*
-*
-
-Enable multiple ethernet devices on your machine by
-adding this line to your /etc/lilo.conf,
-and re-run lilo:
-
-append = "ether=,,eth1"
-
-
-
-
-If you have three interfaces on your bridge, use this line instead:
-
-append = "ether=,,eth1 ether=,,eth2"
-
-
-
-
-More interfaces can be found by adding more ether statements.
-By default a stock Linux kernel probes for a single ethercard,
-and once one is found the probe ceases. The above append statement
-tells the kernel to keep probing for more ethernet devices after the
-first one is found.
-Alternatively, the boot parameter can be used instead:
-
-linux ether=,,eth1
-
-
-
-
-Or, with 3 interfaces, use:
-
-linux ether=,,eth1 ether=,,eth2
-
-
-
-*
-*
-
-Recompile the kernel with BRIDGING enabled.
-
-
-
-*
-*
-
-A bridge should not have an IP address.
-It CAN, but a plain bridge doesn't need one.
-To remove the IP address from your bridge, go to
-/etc/sysconfig/network-scripts/ (for a !RedHat system)
-and copy ifcfg-lo0 to ifcfg-eth0 8
-ifcfg-eth1.
-In these two new files, change the line containing
-__DEVICE=lo__ to __DEVICE=eth0__
-and __DEVICE=eth1__.
-Since other distributions may deviate from this, you may need to refer to additional
-documentation.
-If there are more than 2 interfaces to this bridge,
-be sure to make the corresponding configurations to those, as well.
-
-
-
-*
-*
-
-Reboot so you are running the new kernel with BRIDGING in it,
-and also to make sure that an IP addresses are not bound to the
-network interfaces.
-
-
-
-*
-*
-
-Once the system is backed up, put the ethernet cards into promiscuous mode,
-so they will look at every packet that passes by its interface:
-
-ifconfig eth0 promisc ; ifconfig eth1 promisc
-All interfaces which are connected to network segments to be bridged
-are to be put into promiscuous mode.
-
-
-
-*
-*
-
-Turn bridging ON using the brcfg program:
-
-brcfg -ena
-
-
-
-*
-*
-
-Verify that there is different traffic on each interface:
-
-tcpdump -i eth0 (in one window)
-tcpdump -i eth1 (in another window)
-
-
-
-
-*
-*
-
-Run a sniffer or tcpdump on another machine
-to verify the bridge is separating the segment correctly.
-
-
-
-*
-
-----
-!!!2. Common Problems; Q: I get the message ioctl(SIOCGIFBR) failed: Package not installed
-. What does this mean?; Q: Machines on one side cannot ping the other side!; Q: I cannot telnet/ftp from the bridge! Why?; Q: What do I need to set up in the way of routing?; Q: The bridge appears to work, but why doesn't traceroute show the bridge as a part of the path?; Q: Is it necessary to compile IP_FORWARD into the kernel?; Q: Why are the physical ethernet addresses for port 1 and port 2 the
-same according to the brcfg program?
-Shouldn't they be different?; Q: Bridging does not appear to be an option when performing a make
-config on the kernel. How does one enable it?; Q: Too many hubs (4 or more) are chained one after another in series,
-cause timing problems on an ethernet. What effect does a bridge
-have in a subnet that is layered with hubs?; Q: Can a bridge interface to both 10Mb and 100Mb ethernet segments?
-Will such a configuration slow down the rest of the traffic on the
-high speed side?
-
-__Q: __I get the message ioctl(SIOCGIFBR) failed: Package not installed
-. What does this mean?
-
-
-
-__A: __You don't have bridging capability in your kernel.
-Get a 2.0 or greater kernel,
-and recompile with the BRIDGING option enabled.
-
-
-
-__Q: __Machines on one side cannot ping the other side!
-
-
-
-__A: __
-Did you enable bridging using brcfg -ena? (brcfg should say bridging is ENABLED)
-
-Did you put the interfaces into promiscuous mode?
-(issue the ifconfig command.
-The PROMISC flag should be on for
-both interfaces.)
-
-If using multiple-media interface adapters,
-make sure that the correct one is enabled.
-You may need to use the config/setup program that
-came with the network interface card.
-
-
-
-
-__Q: __I cannot telnet/ftp from the bridge! Why?
-
-
-
-__A: __This is because there is no IP address bound to any of bridge
-interfaces. A bridge is to be a transparent part of a network.
-
-
-
-__Q: __What do I need to set up in the way of routing?
-
-
-
-__A: __Nothing!
-All routing intelligence is handled by
-the bridging code in the kernel.
-To see the ethernet addresses as they are learned by the bridge,
-use the brcfg program in debug mode:
-
-
-brcfg -deb
-
-
-__Q: __The bridge appears to work, but why doesn't traceroute show the bridge as a part of the path?
-
-
-
-__A: __Due to the nature of a bridge, a traceroute should NOT show the bridge as a part of the path. A bridge is to be a transparent component of the network.
-
-
-
-__Q: __Is it necessary to compile IP_FORWARD into the kernel?
-
-
-
-__A: __No. The bridging code in the kernel takes care of the packet
-transport.
-IP_FORWARD is for a gateway that has IP addresses
-bound to its interfaces.
-
-
-
-__Q: __Why are the physical ethernet addresses for port 1 and port 2 the
-same according to the brcfg program?
-Shouldn't they be different?
-
-
-
-__A: __No. Every port on a bridge intentionally is assigned the same
-physical ethernet address by the bridging code.
-
-
-
-__Q: __Bridging does not appear to be an option when performing a make
-config on the kernel. How does one enable it?
-
-
-
-__A: __During the kernel config, answer "Y" to the question, Prompt for
-development and/or incomplete code/drivers (CONFIG_EXPERIMENTAL)
[[Y/n/?
].
-
-
-
-__Q: __Too many hubs (4 or more) are chained one after another in series,
-cause timing problems on an ethernet. What effect does a bridge
-have in a subnet that is layered with hubs?
-
-
-
-__A: __A bridge resets the 3/4/5 hubs rule. A bridge does not deal with
-packets the way a hub does, and is therefore not a contributor to
-timing problems on a network.
-
-
-
-__Q: __Can a bridge interface to both 10Mb and 100Mb ethernet segments?
-Will such a configuration slow down the rest of the traffic on the
-high speed side?
-
-
-
-__A: __Yes, a bridge can tie together a 10Mb segment with a 100Mb segment.
-As long as the network card on the fast network is 100Mb capable,
-TCP takes care of the rest. While it's true that the
-packets from a host in the 100Mb network communicating to a host
-in the 10Mb network are moving at only 10Mb/s, the rest of the
-traffic on the fast ethernet is not slowed down.
-
-----
-!!!3. Copyright
-
-Copyright © 2002 Christopher Cole
-
-
-
-Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts and no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License".
-
-----
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-
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-
-If you have no Invariant Sections, write "with no Invariant
-Sections" instead of saying which ones are invariant. If you have
-no Front-Cover Texts, write "no Front-Cover Texts" instead of
-"Front-Cover Texts being LIST"; likewise for Back-Cover
-Texts.
-
-
-
-If your document contains nontrivial examples of program
-code, we recommend releasing these examples in parallel under your
-choice of free software license, such as the GNU General Public
-License, to permit their use in free software
.
+Describe
[HowToBridge
] here
.
