VMWare Replicas, MAC Conflict Resolution & DHCP Reservations

VMware specific discussions

VMWare Replicas, MAC Conflict Resolution & DHCP Reservations

Veeam Logoby Novox » Sat Oct 01, 2016 9:07 pm

If all VEEAM replicas automatically get new MAC addresses when vCenter notices a MAC address conflict (to fix the conflict), how then can DHCP address reservations work?

Am I not supposed to use DHCP address reservations for my VM's? When replicas are brought online, VM's (which may need to have an IP that doesn't change) get a new, non-reserved, IP address from DHCP... What do other people do in this circumstance? :?:
Novox
Influencer
 
Posts: 11
Liked: never
Joined: Tue Jul 12, 2016 12:51 pm

Re: VMWare Replicas, MAC Conflict Resolution & DHCP Reservat

Veeam Logoby Shestakov » Sat Oct 01, 2016 9:54 pm

Hello,
when replicated VM gets registered, it does have the same MAC address, but then vCenter Server/ESXi host updates it with a new value.
DHCP reservation is not needed and it doesn`t make any difference, however, VBR offers Network Mapping and Re-IP options.
Shestakov
Veeam Software
 
Posts: 4854
Liked: 394 times
Joined: Wed May 21, 2014 11:03 am
Location: Saint Petersburg
Full Name: Nikita Shestakov

Re: VMWare Replicas, MAC Conflict Resolution & DHCP Reservat

Veeam Logoby Novox » Sun Oct 02, 2016 3:00 pm

"DHCP reservation is not needed..." I USE DHCP reservations... When MAC addresses change, DHCP reservations don't work. Does this mean I'm prohibited from using DHCP reservations for VM's?

If all VM's must always use static IP's, I've not seen anything indicating that. If true, it would seem like a huge limitation. What happens when the VM guest re-enumerates NICs and the static IP information is lost in the registry to a non-existent NIC?
Novox
Influencer
 
Posts: 11
Liked: never
Joined: Tue Jul 12, 2016 12:51 pm

Re: VMWare Replicas, MAC Conflict Resolution & DHCP Reservat

Veeam Logoby Shestakov » Sun Oct 02, 2016 5:18 pm

Sorry, I didn`t find in your initial post that you actually use DHCP reservation, thought it was more like generic question.
Novox wrote:When MAC addresses change, DHCP reservations don't work. Does this mean I'm prohibited from using DHCP reservations for VM's?

You can`t have 2 VMs with same MAC address and once vCenter Server changes MAC address of the replicated VM it will have another IP address out of DHCP reservation rules. Could you explain what you are trying to achieve?
You are not prohibited from using DHCP reservations and that will not mess up replication process. Just curious where the confusion is.
Thanks!
Shestakov
Veeam Software
 
Posts: 4854
Liked: 394 times
Joined: Wed May 21, 2014 11:03 am
Location: Saint Petersburg
Full Name: Nikita Shestakov

Re: VMWare Replicas, MAC Conflict Resolution & DHCP Reservat

Veeam Logoby Novox » Mon Oct 03, 2016 1:19 am

For instance, one of my VM's is a web server, I need its IP to not change. I use DHCP address reservations to control my server's IP addresses.

During normal operation, the IP address doesn't change because the MAC address doesn't change. If however, that VM fails and I have to bring a replica online, it will have a different MAC address (because vCenter "helps" by changing the MAC address to something else when a duplicate is detected). DHCP will not provide this new MAC address the same reserved IP as before, which breaks my requirement of the IP not changing.

Is it simply a matter of bad practice to use DHCP reservations in this manner? If so, even with static IP addresses, if the replica VM re-enumerates the NICs, finds a "new" one (new MAC), won't it orphan the first NIC AND the associated static IP address?

MAC addresses WILL change, so DHCP reservation for IP assignment seems out. NICs might? get re-enumerated, so static IP assignment seems out...

Is there a best practice for ensuring that a replica, in a disaster situation, will have the same IP as it's originating VM?
Novox
Influencer
 
Posts: 11
Liked: never
Joined: Tue Jul 12, 2016 12:51 pm

Re: VMWare Replicas, MAC Conflict Resolution & DHCP Reservat

Veeam Logoby Shestakov » Mon Oct 03, 2016 11:14 am

You are right.

If you want replicated VM with same IP address you should give the static IP manually. There will be no conflict because replica VM will be powered-off until failover occurs.

DHCP reservation just won`t be applied because replica will have another MAC.
The scenario with static IP for replica is part of best practices to preserve same IP address, I would suggest to test it in your lab with non-production VMs.

Thanks!
Shestakov
Veeam Software
 
Posts: 4854
Liked: 394 times
Joined: Wed May 21, 2014 11:03 am
Location: Saint Petersburg
Full Name: Nikita Shestakov


Return to VMware vSphere



Who is online

Users browsing this forum: adrian.scurtu, Google [Bot], SyNtAxx and 23 guests

cron