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Hello Everyone,

I am in the process of moving our ESXi hosts from one switch that no longer has any free ports to a new redundant Cisco 3750 stack.  I configured the new switch stack to have the same port settings as the old one.  I performed a vMotion of all of the VMs on host1 to host2 and then physically moved the Ethernet cables one at a time to the new switch stack.  We have two NICs setup for management and two more for VM traffic  I broke these up across the stack to have redundancy should of the the switches in the stack fail.  Within vCenter I did not change any settings on either host1 or host2.

When I migrated our Windows 2008 DHCP server back to host1 (connected to the new switch stack) it would no longer hand out DHCP addresses.  I logged into the console, verified the IP address was correct  and was able to ping various hosts on our network.  The DHCP service was running, but it would still not work properly.  I disabled and enabled the NIC on the DHCP server and restarted the DHCP service but it would still not work.  I then moved the DHCP server hack to host2 (connected to the old switch) and it started handing out addresses right away.

I did the same process with other VMs and none of those had any troubles.  Any idea as to what the issue might be?

Thanks,
Alan

Alan Nord, CCNA
Network Administrator 
Information Technology Services
Macalester College
1600 Grand Avenue
St. Paul, MN 55105

********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/groups/.

Comments

When you Vmotion, does the MAC address move with the virtual server or does the server get a new MAC address?  If it gets a new MAC, then there is a possibility that the ARP cache on the router will keep the old MAC address for up to 4 hours.  You can quickly verify this by "show ip arp" and if needed, "clear ip arp".
 
Good luck,
 
Tristan
 
--
Tristan Rhodes
Network Engineer
Weber State University
(801) 626-8549


>>> On 10/1/2012 at 9:46 AM, in message <CACj5itjztpPNcuUigURkJQwzxkbjbdCDLx9WBdPh+Tkrxhd7Ow@mail.gmail.com>, Alan Nord <anord@MACALESTER.EDU> wrote:
Hello Everyone,

I am in the process of moving our ESXi hosts from one switch that no longer has any free ports to a new redundant Cisco 3750 stack. I configured the new switch stack to have the same port settings as the old one. I performed a vMotion of all of the VMs on host1 to host2 and then physically moved the Ethernet cables one at a time to the new switch stack. We have two NICs setup for management and two more for VM traffic I broke these up across the stack to have redundancy should of the the switches in the stack fail. Within vCenter I did not change any settings on either host1 or host2.

When I migrated our Windows 2008 DHCP server back to host1 (connected to the new switch stack) it would no longer hand out DHCP addresses. I logged into the console, verified the IP address was correct and was able to ping various hosts on our network. The DHCP service was running, but it would still not work properly. I disabled and enabled the NIC on the DHCP server and restarted the DHCP service but it would still not work. I then moved the DHCP server hack to host2 (connected to the old switch) and it started handing out addresses right away.

I did the same process with other VMs and none of those had any troubles. Any idea as to what the issue might be?

Thanks,
Alan

Alan Nord, CCNA
Network Administrator
Information Technology Services
Macalester College
1600 Grand Avenue
St. Paul, MN 55105

********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/groups/.

********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/groups/.

Are you using DHCP snooping on the switches or any other switches in the chain?

 

-Brian

 

On second thought, if you can ping it from other networks, then the ARP entry is correct.
 
My next idea is this; are you using DHCP snooping?  If so, make sure you have configured it the same on all of your switches (even uplink switches).
 
Tristan
 
--
Tristan Rhodes
Network Engineer
Weber State University
(801) 626-8549


>>> On 10/1/2012 at 10:02 AM, in message <50696A1A020000B9000C2CE2@campusvs.weber.edu>, Tristan Rhodes <tristanrhodes@WEBER.EDU> wrote:
When you Vmotion, does the MAC address move with the virtual server or does the server get a new MAC address?  If it gets a new MAC, then there is a possibility that the ARP cache on the router will keep the old MAC address for up to 4 hours.  You can quickly verify this by "show ip arp" and if needed, "clear ip arp".
 
Good luck,
 
Tristan
 
--
Tristan Rhodes
Network Engineer
Weber State University
(801) 626-8549


>>> On 10/1/2012 at 9:46 AM, in message <CACj5itjztpPNcuUigURkJQwzxkbjbdCDLx9WBdPh+Tkrxhd7Ow@mail.gmail.com>, Alan Nord <anord@MACALESTER.EDU> wrote:
Hello Everyone,

I am in the process of moving our ESXi hosts from one switch that no longer has any free ports to a new redundant Cisco 3750 stack. I configured the new switch stack to have the same port settings as the old one. I performed a vMotion of all of the VMs on host1 to host2 and then physically moved the Ethernet cables one at a time to the new switch stack. We have two NICs setup for management and two more for VM traffic I broke these up across the stack to have redundancy should of the the switches in the stack fail. Within vCenter I did not change any settings on either host1 or host2.

When I migrated our Windows 2008 DHCP server back to host1 (connected to the new switch stack) it would no longer hand out DHCP addresses. I logged into the console, verified the IP address was correct and was able to ping various hosts on our network. The DHCP service was running, but it would still not work properly. I disabled and enabled the NIC on the DHCP server and restarted the DHCP service but it would still not work. I then moved the DHCP server hack to host2 (connected to the old switch) and it started handing out addresses right away.

I did the same process with other VMs and none of those had any troubles. Any idea as to what the issue might be?

Thanks,
Alan

Alan Nord, CCNA
Network Administrator
Information Technology Services
Macalester College
1600 Grand Avenue
St. Paul, MN 55105

********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/groups/.

********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/groups/.

********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/groups/.

Yes, we have DHCP snooping set on our core.  The old switch has another switch between itself and the core, the new switch stack is connected directly into the core.  The vlan the DHCP server is in has snooping enabled.

Here is what is on the core:
ip dhcp snooping vlan 5
ip dhcp snooping

Thanks,
Alan

Alan Nord, CCNA
Network Administrator 
Information Technology Services
Macalester College
1600 Grand Avenue
St. Paul, MN 55105



ip dhcp snooping trust

 

You’ll need to make sure the above command is configured on any interface DHCP offers from the DHCP servers will come into any  switch on.

 

-Brian

 

From: The EDUCAUSE Network Management Constituent Group Listserv [mailto:NETMAN@LISTSERV.EDUCAUSE.EDU] On Behalf Of Alan Nord
Sent: Monday, October 01, 2012 12:11 PM
To: NETMAN@LISTSERV.EDUCAUSE.EDU
Subject: Re: [NETMAN] DHCP Server Problem After vMotion and Switch Change

 

Yes, we have DHCP snooping set on our core.  The old switch has another switch between itself and the core, the new switch stack is connected directly into the core.  The vlan the DHCP server is in has snooping enabled.

 

Here is what is on the core:

ip dhcp snooping vlan 5

ip dhcp snooping

 

Thanks,

Alan

 

Alan Nord, CCNA

Network Administrator 
Information Technology Services
Macalester College
1600 Grand Avenue
St. Paul, MN 55105



Are you trusting the server port, the uplinks (including the port-channel interface)?
 
interface x/x
ip dhcp snooping trust
 
You can also look for failures with:
 
show ip dhcp snooping statistics
 
Sometimes you get interesting logs about this as well, "show log".
 
Cheers,
 
Tristan
 
--
Tristan Rhodes
Network Engineer
Weber State University
(801) 626-8549


>>> On 10/1/2012 at 10:11 AM, in message <CACj5iti0KgJ=QK3mWhc=Kwapir=U94sfeszedMq+r260GMxnPQ@mail.gmail.com>, Alan Nord <anord@MACALESTER.EDU> wrote:
Yes, we have DHCP snooping set on our core. The old switch has another switch between itself and the core, the new switch stack is connected directly into the core. The vlan the DHCP server is in has snooping enabled.

Here is what is on the core:
ip dhcp snooping vlan 5
ip dhcp snooping

Thanks,
Alan

Alan Nord, CCNA
Network Administrator
Information Technology Services
Macalester College
1600 Grand Avenue
St. Paul, MN 55105



Thank you Brian and Tristan.  This sure sounds like it would cause the problem I saw.  I am not all that familiar with the concept to be honest so I will need to do some reading to see how my predecessor configured this on the network.

Alan Nord, CCNA
Network Administrator 
Information Technology Services
Macalester College
1600 Grand Avenue
St. Paul, MN 55105



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