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VMWare Datastore inactive but Status Normal

I got this issue with my iSCSI disk provided by Microsoft Windows Server. I am able to access the iSCSI datastore, all of my Virtual Machines are operational with any issue, my iSCSI datastore is showing as inactive but its status is showing normal.
It happend after I had removed iSCSI targets from Windows but and added new target after some time.
What I did;
Rescanned all datastore multiple times --- no luckrestarted management services from SSH of all ESXi hosts with command $ services.sh restart --- no luckRemoved and re-added targets from iSCSI (Windows) Side --- no luckRemoved few VMs which were in inaccessible state and then rescanned datastore --- no luck Finally restarted each ESXi host at a time, it solved the problem.

Connection control operation failed for disk 'ide1:0'

I was getting this error while removing Operating System ISO image mounted on the Virtual Machine.

What worked for me, is
1. Uncheck the "Connected and Connect at power on" from Device Status.
2. Then Change the Device type from "Datastore ISO File to Client Device" Radio Button
3. and press OK to save the changes.

Note:- I was able to remove the mounted ISO only by directly logging to the ESXi at https://esxi-ip-address/ui

where it asks

"The guest operating system has locked the CD-ROM door and is probably using the CD-ROM, which can prevent the guest from recognizing media changes. If possible, eject the CD-ROM from inside the guest before disconnecting. Disconnect anyway and override the lock?"

You need to select yes to eject the CD-ROM and then remove the ISO file successfully.

snmpwalk End of MIB

[root@monitoring ~]#  snmpwalk -c public -v1 10.0.33.228
End of MIB

I was trying to do snmwalk walk for a Cisco Router in GNS3, and was getting only End of MIB after a snmpwalk command.  It turned out that in my Cisco Router configurations I had allowed my SNMP host with ip address with community string "public" but I had not configured the community string separatly with the command  #snmp-server community public
This was my configuration mistake but took some time to figure it out

GNS3 Docker Error while creating node: Docker has returned an error: Cannot connect to host docker:80

Error while creating node: Docker has returned an error: Cannot connect to host docker:80 ssl:False [No such file or directory]

After adding docker template for Alpine Linux in gns3, you get above mentioned message when you want to use alpine linux in GNS3.

To get rid of this message you have to install Docker by following below link
curl -fsSL https://get.docker.com/ | sh

If you do not have curl installed then instal curl first with below command.apt-get install curl
After installing Docker you need to add your user name in the docker group with the following command. $ sudo usermod -aG docker your_username

Verify if the docker service is started with following command$ service docker status
If docker is not started then start with following command $ sudo service docker start
Logout from GNS3 Virtual Machines and log back. Start gns3 and use alpine linux.

Advantage of using System ID extension in Switch Bridge ID

The format of the original 802.1d bridge ID was redefined from two byte priority + MAC address to System ID extension mainly due to the advent of multiple spanning trees as supported by Per VLAN Spanning Tree Plus (PVST+) and IEEE 802.1s Multiple Spanning Trees (MST). With the old-style bridge ID format, a switch’s bridge ID for each STP instance (possibly one per VLAN) was identical if the switch used a single MAC address when building the bridge ID. Having multiple STP instances with the same bridge ID was confusing, so vendors such as Cisco Systems used a different Ethernet BIA for each VLAN when creating the old-style bridge IDs. This provided a different bridge ID per VLAN, but it consumed a large number of reserved BIAs in each switch. 
The System ID Extension allows a network to use multiple instances of STP, even one per VLAN,  but without the need to consume a separate BIA on each switch for each STP instance. The System ID Extension field allows the VLAN ID to be placed int…

How to configure Default Gateway on Nexus 1000v

In case you are finding it hard to reach default gateway from your newly installed Nexus 1000v virtual machine, here is one quick thing to check and configure before you can reach to the default gateway and other allowed subnets from your Nexus 1000v VM.

Configure the management IP Address and default gateway on Nexus 1000v as per below commands

conf t
interface mgmt 0
ip address 192.168.0.100/24
exit
vrf context management
ip route 0.0.0.0/0 192.168.0.1
exit
copy run start

Note: Change the IP address as per your subnet.

Why STP Bridge Priority is Configured in increment of 4096

Spanning-tree operation requires that each switch have a unique BID (Bridge ID). In the original 802.1D standard, the BID was composed of the bridge priority and the MAC address of the switch, and all VLANs were represented by a CST, Common Spanning Tree. Because Cisco started to use unique instance in PVST+ PVRST+ for each VLAN STP Process, there came need to provide Unique BID for each separate instance of STP per VLAN. So what Cisco Did! divided the Bridge priority field of 16 bits into two parts, 4 bits for priority and 12 bits for VLAN ID and named it as Extended VLAN ID. Now because only left most four bits are reserved for Bridge priority, you can only make the combinations of discrete values in increments of 4096 with those bits.