277 lines
5.2 KiB
HTML
277 lines
5.2 KiB
HTML
<HTML
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><HEAD
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><TITLE
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>Load sharing over multiple interfaces</TITLE
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NAME="GENERATOR"
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TITLE="The Intermediate queueing device (IMQ)"
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>Linux Advanced Routing & Traffic Control HOWTO</TH
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><H1
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><A
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NAME="LARTC.LOADSHARE"
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></A
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>Chapter 10. Load sharing over multiple interfaces</H1
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><DIV
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CLASS="TOC"
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><DL
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><DT
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><B
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>Table of Contents</B
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></DT
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><DT
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>10.1. <A
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HREF="lartc.loadshare.caveats.html"
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>Caveats</A
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></DT
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><DT
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>10.2. <A
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HREF="lartc.loadshare.other.html"
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>Other possibilities</A
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></DT
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></DL
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></DIV
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><P
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>There are several ways of doing this. One of the easiest and straightforward
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ways is 'TEQL' - "True" (or "trivial") link equalizer. Like most things
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having to do with queueing, load sharing goes both ways. Both ends of a link
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may need to participate for full effect.</P
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><P
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>Imagine this situation:</P
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><P
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> <TABLE
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BORDER="1"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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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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> +-------+ eth1 +-------+
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| |==========| |
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'network 1' ----| A | | B |---- 'network 2'
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| |==========| |
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+-------+ eth2 +-------+</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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><P
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>A and B are routers, and for the moment we'll assume both run Linux. If
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traffic is going from network 1 to network 2, router A needs to distribute
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the packets over both links to B. Router B needs to be configured to accept
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this. Same goes the other way around, when packets go from network 2 to
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network 1, router B needs to send the packets over both eth1 and eth2.</P
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><P
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>The distributing part is done by a 'TEQL' device, like this (it couldn't be
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easier):</P
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><P
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> <TABLE
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BORDER="1"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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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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># tc qdisc add dev eth1 root teql0
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# tc qdisc add dev eth2 root teql0
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# ip link set dev teql0 up</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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><P
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>Don't forget the 'ip link set up' command!</P
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><P
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>This needs to be done on both hosts. The device teql0 is basically a
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roundrobbin distributor over eth1 and eth2, for sending packets. No data
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ever comes in over an teql device, that just appears on the 'raw' eth1 and
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eth2.</P
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><P
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>But now we just have devices, we also need proper routing. One way to do
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this is to assign a /31 network to both links, and a /31 to the teql0 device
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as well:</P
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><P
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>FIXME: does this need something like 'nobroadcast'? A /31 is too small to
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house a network address and a broadcast address - if this doesn't work as
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planned, try a /30, and adjust the ip addresses accordingly. You might even
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try to make eth1 and eth2 do without an IP address!</P
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><P
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>On router A:
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<TABLE
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BORDER="1"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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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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># ip addr add dev eth1 10.0.0.0/31
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# ip addr add dev eth2 10.0.0.2/31
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# ip addr add dev teql0 10.0.0.4/31</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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><P
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>On router B:
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<TABLE
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BORDER="1"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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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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># ip addr add dev eth1 10.0.0.1/31
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# ip addr add dev eth2 10.0.0.3/31
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# ip addr add dev teql0 10.0.0.5/31</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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><P
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>Router A should now be able to ping 10.0.0.1, 10.0.0.3 and 10.0.0.5 over the
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2 real links and the 1 equalized device. Router B should be able to ping
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10.0.0.0, 10.0.0.2 and 10.0.0.4 over the links.</P
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><P
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>If this works, Router A should make 10.0.0.5 its route for reaching network
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2, and Router B should make 10.0.0.4 its route for reaching network 1. For
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the special case where network 1 is your network at home, and network 2 is
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the Internet, Router A should make 10.0.0.5 its default gateway.</P
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>Prev</A
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>The Intermediate queueing device (IMQ)</TD
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WIDTH="34%"
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> </TD
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>Caveats</TD
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