177 lines
3.2 KiB
HTML
177 lines
3.2 KiB
HTML
<HTML
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>Caveats</TITLE
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NAME="GENERATOR"
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CONTENT="Modular DocBook HTML Stylesheet Version 1.7"><LINK
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REL="HOME"
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TITLE="Linux Advanced Routing & Traffic Control HOWTO"
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HREF="index.html"><LINK
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TITLE="Load sharing over multiple interfaces"
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TITLE="Load sharing over multiple interfaces"
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HREF="lartc.loadshare.html"><LINK
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TITLE="Other possibilities"
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HREF="lartc.loadshare.other.html"></HEAD
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>Linux Advanced Routing & Traffic Control HOWTO</TH
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>Prev</A
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>Chapter 10. Load sharing over multiple interfaces</TD
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NAME="LARTC.LOADSHARE.CAVEATS"
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>10.1. Caveats</H1
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><P
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>Nothing is as easy as it seems. eth1 and eth2 on both router A and B need to
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have return path filtering turned off, because they will otherwise drop
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packets destined for ip addresses other than their own:</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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># echo 0 > /proc/net/ipv4/conf/eth1/rp_filter
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# echo 0 > /proc/net/ipv4/conf/eth2/rp_filter</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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>Then there is the nasty problem of packet reordering. Let's say 6 packets
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need to be sent from A to B - eth1 might get 1, 3 and 5. eth2 would then do
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2, 4 and 6. In an ideal world, router B would receive this in order, 1, 2,
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3, 4, 5, 6. But the possibility is very real that the kernel gets it like
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this: 2, 1, 4, 3, 6, 5. The problem is that this confuses TCP/IP. While not
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a problem for links carrying many different TCP/IP sessions, you won't be
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able to to a bundle multiple links and get to ftp a single file lots faster,
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except when your receiving or sending OS is Linux, which is not easily
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shaken by some simple reordering.</P
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><P
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>However, for lots of applications, link load balancing is a great idea.</P
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>Prev</A
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>Next</A
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VALIGN="top"
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>Load sharing over multiple interfaces</TD
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WIDTH="34%"
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ALIGN="center"
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>Up</A
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>Other possibilities</TD
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> |