<div dir="ltr">Hi There.<br><br><div>What I find odd is that according to section 5.3 of this document <span style="color:rgb(34,34,34);font-family:verdana,arial,helvetica,sans-serif;font-size:14px;line-height:20px;background-color:rgb(250,250,250)"> </span><a href="https://tools.ietf.org/pdf/draft-ietf-dhc-failover-12.pdf" target="_blank">IETF Internet Draft - DHCP Failover Protocol</a> <b>only one</b> of the servers should respond to the DHCP offer. The other should discard it.</div><div><br></div><div>I have tested this behavior with 2 computers connected on the same subnet as the DHCP servers (so no relay agent involved) and it works as described. Both servers receives the offer but only one of them responds with an offer. This is also back up by RFC <span style="color:rgb(0,0,0);font-size:1em;line-height:normal">3074</span> <span style="font-size:1em;line-height:0pt;color:rgb(0,0,0)"><a href="https://tools.ietf.org/html/rfc3074" target="_blank">DHC Load Balancing Algorithm</a>:</span></div><div><span style="font-size:1em;line-height:0pt;color:rgb(0,0,0)"><br></span></div><blockquote style="margin:0 0 0 40px;border:none;padding:0px"><div><span style="font-size:1em;line-height:0pt;color:rgb(0,0,0)"><u>Section 4: </u></span></div>The proposal maps the STID into a hash value using the function in section 6. The resulting hash value can then be used to decide who<br>should respond to the request, or who the forwarding target should be.<br></blockquote><div><br></div><div>So I don't why it's behaving the way it does when there's a relay agent involved. </div><div><br></div><div>Thanks all for your help!</div><div>- Gerónimo.</div><div> </div><br><div class="gmail_quote"><div dir="ltr">El mar., 16 de jun. de 2015 a la(s) 10:28 a. m., Friesen, Don MTIC:EX <<a href="mailto:Don.Friesen@gov.bc.ca" target="_blank">Don.Friesen@gov.bc.ca</a>> escribió:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Yes, this is the expected and normal behavior. Each server will reply with an address from its half of the pool. The machine that is receiving the offers will
take the first offer to arrive and ignore the other.<u></u><u></u></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">We have deployed remote DHCP served by relay for 20 years, and this is how it functions.<u></u><u></u></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">The only annoyance with remote relay DHCP is that the NAK message is a local broadcast.<u></u><u></u></span></p>
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<p class="MsoNormal"><b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:#002060">Don Friesen</span></b><span lang="EN-US" style="font-size:10.0pt;color:#1f497d"><u></u><u></u></span></p>
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<p class="MsoNormal"><b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> <a href="mailto:dhcp-users-bounces@lists.isc.org" target="_blank">dhcp-users-bounces@lists.isc.org</a> [mailto:<a href="mailto:dhcp-users-bounces@lists.isc.org" target="_blank">dhcp-users-bounces@lists.isc.org</a>]
<b>On Behalf Of </b>Patrick Trapp<br>
<b>Sent:</b> Tuesday, June 16, 2015 6:17 AM</span></p></div></div></div></div><div lang="EN-CA" link="blue" vlink="purple"><div><div><div style="border:none;border-top:solid #b5c4df 1.0pt;padding:3.0pt 0cm 0cm 0cm"><p class="MsoNormal"><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif""><br>
<b>To:</b> Users of ISC DHCP<br>
</span></p></div></div></div></div><div lang="EN-CA" link="blue" vlink="purple"><div><div><div style="border:none;border-top:solid #b5c4df 1.0pt;padding:3.0pt 0cm 0cm 0cm"><p class="MsoNormal"><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif""><b>Subject:</b> RE: DHCP Relay agent not forwarding messages to the client<u></u><u></u></span></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt"><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:black">You'll want more experienced answers, I'm sure, but we are running a fair-sized network for our DHCP - I believe around 45000 devices
and roughly 70 subnets. All of those devices find the DHCP servers via relay agents and we are using failover.<br>
<br>
We do generally see two DHCP offers - one from each server - when a device requests an address. I expected that behavior and saw no reason to be concerned with it. I still don't - I am under the impression that this is how the system is designed to work.<br>
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It has worked fine for us in this fashion for years. We deployed this particular solution in 2007, but I believe it was used for other devices prior to that, so we have used this through several iterations of ISC-DHCP.<br>
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Patrick<u></u><u></u></span></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt"><b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:black">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:black">
<a href="mailto:dhcp-users-bounces@lists.isc.org" target="_blank">dhcp-users-bounces@lists.isc.org</a> [<a href="mailto:dhcp-users-bounces@lists.isc.org" target="_blank">dhcp-users-bounces@lists.isc.org</a>] on behalf of Gero Palacio [<a href="mailto:gero.palacio@gmail.com" target="_blank">gero.palacio@gmail.com</a>]<br>
<b>Sent:</b> Monday, June 15, 2015 5:17 PM<br>
<b>To:</b> Users of ISC DHCP<br>
<b>Subject:</b> Re: DHCP Relay agent not forwarding messages to the client</span><span style="color:black"><u></u><u></u></span></p>
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<p class="MsoNormal"><span style="color:black">Hi Simon, <u></u><u></u></span></p>
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<p class="MsoNormal"><span style="color:black"><u></u> <u></u></span></p>
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<p class="MsoNormal"><span style="color:black">Thanks for the reply, I did not know if it was a bug or the correct behavior.<br>
<br>
If I may, let me ask you a follow up question. Does DHCP relay works well with a pair of DHCP servers in failover mode?<br>
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I've configured the relay agent described in my previous email to forward the messages to the pair of DHCP servers. Now everytime the relay agent forwards a discovery message from the host, I receive 2 dhcp offers, one from each server. As I've configured split
to 128, only 1 server should reply with an offer.<br>
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If I test the same configuration with hosts in the same subnet as the DHCP servers, the behavior is as expected. The DHCP servers
<u>responds or ignores</u> the discovery messages according to the result of the hash based on the MAC address of the hosts.<br>
<br>
Any idea what might be the problem? Is it even a good idea to run a relay agent and a pair of DHCP servers in failover?<br>
<br>
Thanks!<br>
Gerónimo.<u></u><u></u></span></p>
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<p class="MsoNormal"><span style="color:black">On Mon, Jun 15, 2015 at 6:18 PM, Simon Hobson <<a href="mailto:dhcp1@thehobsons.co.uk" target="_blank">dhcp1@thehobsons.co.uk</a>> wrote:<u></u><u></u></span></p>
<p class="MsoNormal"><span style="color:black">Gero Palacio <<a href="mailto:gero.palacio@gmail.com" target="_blank">gero.palacio@gmail.com</a>> wrote:<br>
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> CLIENT <---> [eth0] (relay agent) ROUTER-1 [eth1] <---> ROUTER-2 <---> DHCP Server<br>
><br>
> The relay agent runs ONLY on the interface that faces the client, which is eth0: "dhcrelay -4 -i eth0 10.0.1.10"<br>
...<br>
> Can anybody tell me if I'm doing something wrong? Is this a known bug?<br>
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It's a known feature. You must also listen on eth1 in order to get the replies from the server - it's just the way the relay agent works.<br>
<br>
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