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<p class="MsoNormal"><span lang="EN-US">dear,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> There is a question about mtu of vxlan port. In below scene, there are two node(compute or vm), and we send udp packets between two docker with nic’s(eth0) mtu setting to 1500.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Vxlan port’s mtu is 65485 setting in ovs code(we don’t change it). It works well that packet can be sent and receive to/from other docker.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">But we add conntrack flow table in interface of one bridge, such as:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> ovs-ofctl add-flow $1 "table=0,arp,action=resubmit(,1)"<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> ovs-ofctl add-flow $1 "table=0,ip,action=ct(commit,zone=1,table=1)"<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> ovs-ofctl add-flow $1 "table=1,actions=NORMAL"<o:p></o:p></span></p>
<p class="MsoListParagraph" style="margin-left:21.0pt;text-indent:-21.0pt;mso-list:l0 level1 lfo2">
<![if !supportLists]><span lang="EN-US"><span style="mso-list:Ignore">1、<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span lang="EN-US">It is ok with packet length <= 1450 bytes;<o:p></o:p></span></p>
<p class="MsoListParagraph" style="margin-left:21.0pt;text-indent:-21.0pt;mso-list:l0 level1 lfo2">
<![if !supportLists]><span lang="EN-US"><span style="mso-list:Ignore">2、<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span lang="EN-US">but when we send packet length > 1450 bytes, such as 2000 bytes, the packet will be dropped at
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">the vxlan port in the sending node.<o:p></o:p></span></p>
<p class="MsoListParagraph" style="margin-left:21.0pt;text-indent:-21.0pt;mso-list:l0 level1 lfo2">
<![if !supportLists]><span lang="EN-US"><span style="mso-list:Ignore">3、<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span lang="EN-US">if we modi the mtu of vxlan port from 65485 to 1450, it works well when packet length >=1450.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal" style="margin-left:21.0pt"><span lang="EN-US">First when send big udp packet(len>1450), it will be fragged when send from one docker.<o:p></o:p></span></p>
<p class="MsoNormal" style="text-indent:21.0pt"><span lang="EN-US">when add conntrack flow table, udp packet(length>1450) will be deal with do_execute_actions in which “case OVS_ACTION_ATTR_CT” will be called. In this switch case, handle_fragments routine is
called to<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">defrag udp frags. When packet comes to vxlan port, packet is
</span><span class="family-english4"><span lang="EN-US" style="color:#333333">aggregated to one packet with length >1450, then it is compared with mtu of vxlan port, it is less than 65485(mtu length of vxlan port)<o:p></o:p></span></span></p>
<p class="MsoNormal"><span class="family-english4"><span lang="EN-US" style="color:#333333">so it does not frag and pass through to eth0 (mtu=1450), then in routine output_ip it return error code of -90.</span></span><span lang="EN-US"><o:p></o:p></span></p>
<p class="MsoListParagraph" style="margin-left:21.0pt;text-indent:0cm"><span lang="EN-US">When no conntrack flow table is added, big udp packet will not go through “case OVS_ACTION_ATTR_CT” in do_execute_actions, then defrag will not been done. So eack frags
with lengh 1450, can go through vxlan port and eth0.<o:p></o:p></span></p>
<p class="MsoListParagraph" style="margin-left:21.0pt;text-indent:0cm"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal" style="text-indent:21.0pt"><span lang="EN-US">so my question is, why the mtu of vxlan port is set to 65485(so big!), and can it be modified to 1450?
<o:p></o:p></span></p>
<p class="MsoNormal" style="text-indent:21.0pt"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">[scene]:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> [ Docker0] [ Docker1]<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> | |<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> [br_int] [br_int]<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> | |<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> [br_tunnel] [br_tunnel]<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> | | |<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> [vxlan port] | [vxlan port]<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> | | |<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> [eth0] - - - - - - - - |- - - - - - - - - - -- -- - [eth0]
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> |<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> node1 | node 2<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> <o:p></o:p></span></p>
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