multiple bootprelay servers

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We are working on building a more resilient network. One key part is DHCP. Our server team is working on setting up our servers (Windows 2012 R2) to be able to handle the requests. I just need to have our routers be able to forward the request to the proper DHCP server. Currently our routers (x460 EXOS 15.5.2.9) only forwards requests to our one DHCP server (per building) and it works great. If that server goes down or offline for any reason we want users to still be able to obtain an IP address. How do we add a second server to the router. Do we just add a second IP to the bootprelay part of the config

configure bootprelay add vr VR-Default
configure bootprelay add vr VR-Default

If that's the case how does the system keep track of which server it's passing to?

Thanks in advance!
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bw447

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Posted 4 years ago

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John

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You should be able to just add another address.  At least that is the way it works on the S-series.  The system will relay the DHCP packet to both servers.  It lets the DHCP protocol work it out.  Basically the first DHCP packet to make it back to the client wins.  Typically what you do is split the scope 80\20 across the two servers and you tell your secondary server to delay its response by 5 seconds or so.  Check this out.
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Frank

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If I'm not mistaken, Windows 2012 has revamped their DHCP so that you don't even have to split the scopes anymore, but where they both know about all of the assignments.
https://technet.microsoft.com/en-us/library/dn338978.aspx

I wouldn't have thought to ever say this, but that's quite a neat feature Windows has now. Two 2012 servers in failover mode with the new features, two entries on the 460s, and that should be it.
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Bruce Garlock

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Hello, we just configured Win2k12R2 with redundant DHCP, with the secondary acting as a passive (hot standby) role.  On our x-460's which currently have a setting pointing to the primary server, it sounds like we just need to add another line and point it to the IP of the standby server?  
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Erik Auerswald, Embassador

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Yes, adding a second "bootprelay" IP address entry should suffice, if the setup is currently working with relaying to one DHCP server, and both DHCP servers are reached via the same VLAN from the switch.
If the second DHCP server is reached from the switch via another VLAN, you need to ensure that bootprelay is enabled for that VLAN as well.
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Bruce Garlock

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Excellent - thank you.
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bw447

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Thanks for the replies John and Frank. We'll test this out and I'll post the results.