Networking

During the replacement of some VMware ESXi hosts at a customer, I discovered a recurrent failure of the vSphere Distributed Switch health checks. A VLAN and MTU mismatch was reported. On the physical side, the ESXi hosts were connected to two HPE 5820 switches, that were configured as an IRF stack. Inside the VMware bubble, the hosts were sharing a vSphere Distributed Switch.

The switch ports of the old ESXi hosts were configured as Hybrid ports. The switch ports of the new hosts were configured as Trunk ports, to streamline the switch and port configuration.

By accident, I found a heartbeat/ VLAN issue on a NetScaler cluster at one of my customers. The NetScaler ADC appliances have three interfaces connected to a switch stack. Two of the three interfaces were configured as a channel (LAG). This is a snippet from the config:

set channel LA/1 -tagall ON -throughput 0 -lrMinThroughput 0 -bandwidthHigh 0 -bandwidthNormal 0
...
bind vlan 10 -ifnum 1/3
bind vlan 10 -ifnum LA/1 -tagged
bind vlan 54 -ifnum LA/1 -tagged
bind vlan 55 -ifnum LA/1 -tagged

On the switch stack, the port to which interface 1/3 is connected, is configured as an access port. The ports, to which the channel is connected, is configured as a trunk port with some permitted VLANs. The customer is using HPE Comware based switches. The terminology is the same for Cisco. If you use HPE ProVision or Alcatel Lucent Enterprise, translate “access” to “untagged” and “trunk” to “tagged”. Because the channel is configured as a trunk port on the switch, the tagall option was set.

Last friday I passed the 1Y0-351 (Citrix NetScaler 10.5 Essentails and Networking) exam with a pretty good score. The exam was necessary, not only because I will do much more NetScaler projects in the future, but also because Citrix has made it mandatory to have a CCP-N in your company to to sell Citrix NetScaler.

Preparation

My employer booked me a 5-day course (CNS-220 Citrix NetScaler Essentials and Traffic Management). Very nice, although I already had experience with NetScaler deployments. This training was designed for NetScaler 12.0, not for 10.5.

Open network ports in offices, waiting rooms and entrance halls make me curious. Sometimes I  want to plugin a network cable, just to see if I get an IP address. I know many companies that does not care about network access control. Anybody can plugin any device to the network. When talking with customers about network access control, or port security, I often hear their complains about complexity. It’s too complex to implement, to hard to administrate. But it is not sooo complex. In the easiest setup (with mac authentication), you need a switch, that can act as authenticator, and a authentication server. But IEEE 802.1x is not much more complicated.

Starting with release 11.1, NetScaler ADC offers an easy way to redirect traffic from HTTP to HTTPS within the configuration of a load-balanced vServer. With 11.1, Citrix introduced the paramter  -redirectFromPort and -redirectURL.

While playing with a NetScaler ADC in my lab, I discovered a strange error message as I tried to configure the redirect.

Internal vserver couldn’t be set?! Okay, there was already a vServer, that was listening on port 80. After removing the vServer, I was able to setup the redirection and it was working as expected.

I don’t like to use untrusted networks. When I have to use such a network, e.g. an open WiFi network, I use a TLS encrypted tunnel connection to encrypt all web traffic that travels through the untrusted network. I’m using a simple stunnel/ Squid setup for this. My setup consists of three components:

• Stunnel (server mode)
• Squid proxy
• Stunnel (client mode)

What is stunnel?

Stunnel is an OSS project that uses OpenSSL to encrypt traffic. The website describes Stunnel as follows:

I switched my mobile carrier and my new carrier doesn’t offer multi SIM (but hey, it’s cheap and sufficient for my needs). Now I have to use my iPhone as WiFi hotspot. No big deal, works perfect. Except one thing: When I was using the built-in 4G modem in my laptop, Windows 10 knew that it was using a mobile (metered) connection, and suspended some services like OneDrive sync, download of Windows Updates etc. That is pretty handy in times of “flatrates” with single digit GB highspeed data volume.

When I talk to customers and colleagues about cloud offerings, most of them are still concerned about the cloud, and especially about the security of public cloud offerings. One of the most mentioned concerns is based on the belief, that each and every cloud-based VM is publicly reachable over the internet. This can be so, but it does not have to. It relies on your design. Maybe that is only a problem in germany. German privacy policies are the reason for the two german Azure datacenters. They are run by Deutsche Telekom, not by Microsoft.

The HPE OfficeConnect 1920 switch series is designed for SMBs. The switch is perfect for small environments, that require features like VLANs, routing or 802.1x. This switch is smart-managed, so it has “only” a web interface and only a limited CLI.

I have two switches in my lab: A 1910-8G and the successor, a 1920-24G. Although the device supports IPv6, it doesn’t support SLAAC (Stateless Address Autoconfiguration) by default. The switch does not send router advertisements (RA). I’m using IPv6 in my lab (Stateless DHCPv6 + SLAAC), so the missing RAs were a problem for me, or at least, annoying. Fortunately you can change the default behaviour.

In my last post (Routed Port vs. Switch Virtual Interface (SVI)), I have mentioned a consequence of using routed ports to interconnect access and core switches:

You have to route the traffic on the access switches.

Routing on the network access, the edge of the network, is not a question of performance. It is more of a management issue. Depending on the size of your network, and the number of subnets, you have to deal with lots of routes. And think about the effort, if you add, change or remove subnets from your network. This is not what you want to do with static routes. You need a routing protocol.