Networking

One of the benefits of using HP Virtual Connect in C-class blade Chassis is the ability to have MAC Addresses and WWNs set on a server bay as opposed to the physical server. I’m sure you’re aware that each device that has a network card has a Media Access Control (MAC) address which is a burned in identifier that makes that NIC unique. HP decided that it might be nice to control those MAC Addresses in their blade chassis. Before you setup any server profiles, you have the option to choose “Virtual Connect Assigned MAC Addresses”. These are addresses that are assigned to each server bay so that no matter what blade is put into the bay, the MAC addresses will stay the same. You might find this very useful in the case of a failed blade. If you receive a new blade from HP and throw it into the same bay, it will retain all of the same MAC Addresses and thus look the same to your switches. ...

I often hear Port Address Translation (PAT)referred to as Network Address Translation (NAT). Its a pretty common to hear this and is really not a big deal because the two are similar and I know what is meant. But to clear things up I decided to put together a quick post. Network Address Translation NAT is the process of “translating” an IP Address in a router or firewall. This is most commonly done to present a private IP Address into a Public IP Address that is accessible on the Internet. For instance, you may want to have your E-mail server have a public address so that it can route mail. ...

Oh Noes! I sense lolcats in this post. I’ve been seeing Category 6a cable if a few datacenters recently and thought it might be a good idea to review when and why we would use this type of cabling. Wiring The Category 6a cabling is wired the same as Category 5e at 1000BaseTX speeds. Note: that you can get away with splitting two sets of pairs off of Cat5e, but this only allows 100BaseT Ethernet. ...

Jumbo frames can be useful to optimize IP networks, especially in storage networking. This post should help to explain why using jumbo frames can be useful. I’m not Jumbo, I’m just big boned! First, let’s define what we mean by the term jumbo frame. As you can imagine it’s bigger than a normal frame. A Jumbo frame simply means any frame with an MTU larger than 1500 bytes. What exactly does that mean? To really understand that we need to look at an Ethernet frame. The diagram below shows a hastily thrown together Ethernet frame and most of the frame we’re not concerned with for this topic. Parts of the frame are used for determining where the frame is headed, where it came from and to make sure it arrived intact. The section we’re looking at is the “Data” or “Payload” section of the frame. ...

After attending VMworld this year, I decided I needed to try to understand VXLANs a little better. Based off of the basic concept that it stretches a layer two broadcast domain over layer three networks, I was worried that I knew how this was accomplished. What is VXLAN? VXLAN stands for Virtual Extensible LAN and is a fairly new method of making the datacenter network elastic. Suppose for example that you want to be able to move your virtual machines from your own server room to a co-location and then to a public cloud depending on what the load was on your environment. In order to do this without causing downtime, you’d need a way for your layer two ethernet frames to continue getting from your clients to your servers even, if a router is in that path. ...

I gave an overview of how HP blades are mapped to Virtual Connect Interconnect Modules in my last post. /2012/08/09/hp-virtual-connect-basics This post focus more on understanding the networks created through HP Virtual Connect Manager. In the last post I described out blade NICs map to the Interconnect Bays in the back of an HP C7000 Chassis using the downlinks. Now let’s talk about how those NICs can get added to a specific Network. HP calls these networks inside of a c7000 chassis “vNets”. ...

HP Virtual Connect is a great way to handle network setup for an HP Blade Chassis. When I first started with Virtual Connect it was very confusing for me to understand where everything was, and how the blades connected to the interconnect bays. This really is fairly simple, but might be confusing to anyone that’s new to this technology. Hopefully this post will give newcomers the tools they need to get started. ...

Suppose you have multiple virtual machines that you would like to distribute load across that are housed inside of your virtual environment. How do we go about setting up Network Load Balancing so that it will still work with things like DRS and VMotion? Switch Refresher In most networks we have switches that listen for MAC addresses and store them in their MAC Address Table for future use. If a switch receives a request and it knows which port the destination MAC address is associated with, it will forward that request out the single port. If a switch doesn’t know which port a MAC Address is associated with, it will basically send that frame out all of it’s ports (known as flooding) so that the destination can hopefully still receive it. This is why we’ve moved away from hubs and moved towards switches. Hubs will flood everything because they don’t keep track of the MAC Addresses. You can see how this extra traffic on the network is unwanted. ...

A question often comes up about what to do when you have a segmented virtual network that needs to be able to traverse subnets. This might happen if you’re doing some testing and don’t want the machines to contact the production network, or perhaps doing a test SRM failover and having the virtual machines in their own test network. Virtual machines in subnet (A) might need to contact other virtual machines in subnet (B) but don’t have access to the physical router any longer, so they can’t communicate. To solve this issue, how about we try a virtual router? ...

Many services such as DHCP or TFTP use broadcast packets to find a particular server. In the case of DHCP, a device when connecting to a network will send out a broadcast to find a DHCP server to get an IP address to use. But what if you have multiple subnets on your network? You could have a DHCP server on each of your subnets, but this seems a bit overkill. ...