Tag Archives: network

Virtual Machine Cannot Get DHCP IP Address

Just a quick post. When virtual machine cannot get DHCP IP address the first thing you want to check is firewall. Whatever Windows firewall or physical firewall. You should make sure UDP port 67 and 68 are not blocked. Otherwise you  will see the virtual machine gets 169.x.x.x IP address only.

The two  ports is required for DHCP client to query IP addresses. The methodology is introduced in RFC document.

DHCP uses UDP as its transport protocol. DHCP messages from a client
to a server are sent to the ‘DHCP server’ port (67), and DHCP
messages from a server to a client are sent to the ‘DHCP client’ port
(68). A server with multiple network address (e.g., a multi-homed
host) MAY use any of its network addresses in outgoing DHCP messages.

I also got some ideas in this post.


Network Latency on Virtual Machine

Slight network latency may cause application problem  on sensitive virtual machines. Even the network responding time is just 3 or 7 ms. There is a way to improve the  stability of responding latency – Enable RSS on NIC.

Network traffic is handled by single CPU core when RSS is disabled. Enable it will distribute the workload to 4 cores by default. You can increase CPU for RSS by change registry.

To summarize the solution. Go to Device Manager -> NIC properties -> Advance -> Find RSS option  and enable it. You will see 2 – 3 network drops when applying it.

You can refer following articles for detail.

Poor network performance or high network latency on Windows virtual machines

Virtual Receive-side Scaling in Windows Server 2012 R2

Regarding increase CPU for RSS. Read following article to learn how to modify it.

Setting the Number of RSS Processors

vRealize Operation Manager Installation Pending on install.sh

If your company implemented firewall and blocked public NTP server, you may see installation of vRealize Operation Manager pending on ./install.sh on console. That’s because the installer tries to negotiate with NTP server http://www.iana.org. The firewall blocked the traffic.

VMware TAM Manager Shan told me  there are two options on firewall to block traffic: REJECT and DROP. REJECT means firewall responding to the request and let source device knows it’s rejected. DROP means firewall immediately ignores the request and no responding to source device. Looks like there is a bug in vROPs code that it hung if NTP request gets drop and no responding.

The workaround is create a port group without physical uplinks and install vRealize Operation  Manager. Then move it to proper network after installation  is completed. You can configure correct IP addresses when import the OVF file so later on you just need simply move the network.

Blue Screen with Bug Check 50 on ESXi 5.x

Some critical VMs got blue screen in last few weeks. After working with OS and hardware vendor, we figured out the root cause eventually. It’s a CPU problem related to Intel v2 CPU of E3, E5 and E7 families. The detail information is documented in VMware KB Windows 2008 R2 and Solaris 10 64-bit virtual machines blue screen or kernel panic when running on ESXi 5.x with an Intel E5 v2 series processor.

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Receive Side Scaling on UCS Blades

To implement enterprise application like SAP, Oracle or SQL on UCS virtualization environment. Default setting of UCS blades may not suitable for the application. We always expect highest performance by optimize hardware and ESXi. In my UCS training session, I noticed one “hidden” parameter may helpful for performance.

Receive Side Scaling – So called RSS, it’s a feature that allows you to utilize multiple CPUs and multiple cores per CPU to process the receiving network load. Without RSS, all of the receive network traffic is processed by one CPU and by only one core of the CPU. Essentially, RSS distributes receiving network load to all of the CPUs and their cores.

The parameter is an option in BIOS, but it’s not under BIOS policy in UCS Manager. You should go to Servers tab, extend Policies node, and check an Eth Adapter Policy under Adapter Policy node, Receive Side Scaling (RSS) is available in Options section of right frame. Blade should be rebooted to leverage the option.

Please keep in mind that do not enable RSS if your adapters more than your CPUs, it will cause unexpected network transmit failed. RSS option must be enabled on UCS policy before enable it on OS layer (I confirmed with Cisco TAC, is that true?). Regarding OS layer, please refer to those articles.

Receive side scaling on Intel® Network Adapters

How to enable Receive Side Scaling on Microsoft Windows Server 2008 R2

You don’t have to enable the option if network traffic is not a concern.

Error: No NIC found with MAC address…

Your HP server may runs fine on ESXi 4.x or 5.0, but you may get error message No NIC found with MAC address xx:xx:xx:xx:xx:xx after upgrade to ESXi 5.1 or later.

That’s caused by network adapter firmware, you have to upgrade server network adapter firmware by HP SPP 2013.02 or later. I would recommend you upgrade firmware of each component to this version, it’s pretty stable to run ESXi 5.1.