Add FAQ 97 about low TC outbound bandwidth

Signed-off-by: Tom Eastep <teastep@shorewall.net>

docs/FAQ.xml

@@ -2188,6 +2188,47 @@ We have an error talking to the kernel
           <member>sch_sfq</member>
         </simplelist></para>
     </section>
+
+    <section id="faq97">
+      <title>(FAQ 97) I enable Shorewall traffic shaping and now my upload
+      rate is way below what I specified</title>
+
+      <para><emphasis role="bold">Answer</emphasis>: This is likely due to TCP
+      Segmentation Offload (TSO) and/or Generic Segmentation Offload (GSO)
+      being enabled in the network adapter. To verify, install the
+      <firstterm>ethtool</firstterm> package and use the -k command:</para>
+
+      <programlisting>root@gateway:~# ethtool -k eth1
+Offload parameters for eth1:
+rx-checksumming: on
+tx-checksumming: on
+scatter-gather: on
+tcp-segmentation-offload: <emphasis role="bold">on</emphasis>
+udp-fragmentation-offload: off
+generic-segmentation-offload: <emphasis role="bold">on</emphasis>
+generic-receive-offload: off
+large-receive-offload: off
+ntuple-filters: off
+receive-hashing: off
+root@gateway:~#</programlisting>
+
+      <para>If that is the case, you can correct the problem by adjusting the
+      <replaceable>minburst</replaceable> setting in
+      /etc/shorewall/tcinterfaces (complex traffic shaping) or
+      /etc/shorewall/tcdevices (simple traffic shaping). We suggest starting
+      at 10-12kb and adjust as necessary. Example (simple traffic
+      shaping):</para>
+
+      <programlisting>#INTERFACE	TYPE		IN-BANDWIDTH			OUT-BANDWIDTH
+eth0		External	50mbit:200kb			5.0mbit:100kb:200ms:100mbit:<emphasis
+          role="bold">10kb</emphasis>
+</programlisting>
+
+      <para>Alternatively, you can turn off TSO and GSO using this command in
+      <filename>/etc/shorewall/init</filename>:</para>
+
+      <programlisting><emphasis role="bold">ethtool -k eth<emphasis>N</emphasis> tso off gso off</emphasis></programlisting>
+    </section>
   </section>
 
   <section id="About">