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Issue
When trying PXE-boot/cloud-boot a Hypervisor, no DHCP requests are seen on the DHCP servers. The HV times out waiting for an IP.
Troubleshooting/symptoms
Plug a laptop or a server with an installed OS on the port managed by the DHCP/PXE-boot environment. You should see an IP given to that server as it requests the IP from the OS (no timeout).
a) /var/log/messages shows that there has been an DHCPrequest:
Dec 12 09:50:50 mgmt01 dhcpd: DHCPREQUEST for 1xxx from 00:21:70:e3:df:ae (DBTOA000) via eth0
Dec 12 09:50:50 mgmt01 dhcpd: DHCPACK on 1xxx to 00:21:70:e3:df:ae (DBTOA000) via eth0
b) and then, the lease file has an entry for the IP :
lease 173.xxxx {
starts 4 2013/12/12 14:50:50;
ends 4 2013/12/12 15:00:50;
binding state active;
next binding state free;
hardware ethernet 00:21:70:e3:df:ae;
uid "\001\000!p\343\337\256";
client-hostname "DBTOA000";
Resolution
1. Disable PortFast on specific ports:
test(config)# interface range GigabitEthernet1/0/1 - 4
test(config-if-range)# spanning-tree portfast
Once this is disabled, there is a possibility to create "loops on your network". To prevent this, use "spanning-tree bpduguard enable". That will set the ports to listen for possible loop packets.
2. You can enable spanning-tree bpduguard on specific ports:
test(config)# interface range GigabitEthernet1/0/1 - 4
test(config-if-range)# spanning-tree portfast bpduguard
Note: Please note that commands may differ. Find the alternative commands by contacting your switch/hardware vendor. The main idea of the solution is to partially disable STP (Spanning tree protocol) on the ports of your Management Network.
Cause
STP makes the server wait for 45 seconds before forwarding traffic to the Port.
Listening Delay= 30
Learning Delay= 15
Total delay of 45 seconds .. PXE-boot times out after 10 Seconds.