Beginner’s Guide to Dell N4000 Series Switches

Dell N-Series switches run on Dell Network Operating System (DNOS) version 6.x. Unlike Dell S-Series switches which run on DNOS 9.x, derived from  Force10 Operation System (FTOS), DNOS 6.x came from the PowerConnect switch series and share the same codebase. So if you’ve ever worked with PowerConnect switches, N-Series syntax should be very familiar.

In my case I had two Dell N4032F switches. But the same set of commands applies to any other N4000 Series switch.

Initial Configuration

When you first turn the switch on, it gives you 60 seconds to enter the wizard, where you can set up network settings for the Out-of-Band (OOB) management interface and change the admin password. If you miss it you can reboot the switch and it will show the same wizard prompt again when it boots up. Or you can set it up from the CLI:

# interface out-of-band
# ip address 10.10.10.10 255.255.255.0 10.10.10.254

# show ip interface out-of-band

Once you get to the CLI prompt, configure hostname and enable SSH:

# hostname n4032f-prod

# crypto key generate rsa
# crypto key generate dsa
# ip ssh server
# ip telnet server disable

Stacking

Dell N4000 Series switches support both stacking and MLAG (Multi-chassis Link Aggregation). One of the drawbacks of the stack configuration is disruptive firmware upgrades. When you update firmware on the stack master, firmware is distributed to all stack members and all switches are rebooted simultaneously.

In MLAG each switch has its own Control Plane and can be rebooted independently. Which is MLAG’s shortcoming at the same time, because unlike stack, where all units act as one switch, in MLAG you have to manage each switch separately.

In my case I chose stacking for its simplicity.

Dell N4000

N4000 switches are stacked using the two 40Gb QSFP ports located at the front. QSFP ports are not configured in stack mode by default. Which you need to change on both switches before you can build a stack:

# stack
# stack-port Fortygigabitethernet 1/1/1 stack
# stack-port Fortygigabitethernet 1/1/2 stack

# show switch stack-ports

Once QSFP ports on both switches are configured, disconnect power from both switches and boot the switch you want to be the stack master first (typically the top switch). When the first switch has fully booted, boot the second switch and check the status. This is what you should see:

# show switch

n4000_stack

Firmware Upgrade

If it’s not a brand new switch, save the config before doing the firmware upgrade:

# copy run start
# copy running-config tftp://10.10.10.100/backup.txt

You can use any TFTP server for the firmware upgrade, such as the free Tftpd64 server.

tftpd64

Then you upload the firmware image to the stack master and reload the stack:

# copy tftp://10.10.10.100/N4000v6.2.7.2.stk backup
# boot system backup
# reload
# show version

Firmware is uploaded to a backup image. Then you select the backup image for the next boot and reload the stack. When both switches reboot you should see something similar to this:

frimware_upgraded

As part of the upgrade process the new firmware is automatically uploaded from the master to all stack members, which is a default behaviour. You can confirm it is enabled using the following command:

# show auto-copy-sw

Flow Control, Jumbo Frames and iSCSI Optimization

In my case I used two N4032F switches for an iSCSI backbone, so I needed to make sure that Flow Control and Jumbo Frames are enabled on the switch.

Flow Control is enabled by default, which you can confirm by the following command:

# show storm-control

To globally enable Jumbo Frames on all ports type:

# system jumbo mtu 9216

# show system mtu

Interestingly, Dell N4000 Series switches also have built-in iSCSI optimization, which can detect iSCSI sessions by snooping the traffic on ports 3260 and 860. It then prioritizes iSCSI traffic over the other types of traffic to guarantee low latency for storage I/O. To show iSCSI settings:

# show iscsi

By default switches only track the sessions. Traffic prioritization is disabled by default and has to be enabled manually. This didn’t matter in my case, as the switches were dedicated for storage traffic. But if you share switches between storage and server traffic, you may want to enable it. Refer to the switch User’s Configuration Guide for details.

If you’re using a Dell Compellent storage array with N4000 switches, also make sure to apply a Compellent profile to the ports where storage array is connected to:

# macro global apply profile-compellent-nas $interface_name te1/0/1
# macro global apply profile-compellent-nas $interface_name te1/0/2
# macro global apply profile-compellent-nas $interface_name te1/0/3
# macro global apply profile-compellent-nas $interface_name te1/0/4

VLANs, Trunks and Port Channels

Again, I didn’t use any VLANs and Trunks, because switches were dedicated for iSCSI traffic and were separate from the LAN core. And I didn’t need Port Channels either, as they are not required for iSCSI.

Your scenario might be different. For instance, if you have vSphere hosts connected to a NetApp array over NFS, you may want to create a Multi-Mode (LACP) VIF on the NetApp side. If that’s the case, to create a port channel on the Multi-Mode VIF ports use the following:

# interface range te1/0/2,te2/0/2
# channel-group 1 mode active
# show intefaces po1

If the switches are used for both storage and VM traffic, then you’ll need to configure the server ports and uplink them to your network core. Create your VLANs first:

# vlan 10,20,30

Configure vSwitch uplinks from the ESXi hosts. In a typical vSphere environment, traffic is tagged on the vSwitch side, which means that server ports should be configured as trunks:

# interface range te1/0/3-6,te2/0/3-6
# switchport mode trunk
# switchport trunk allowed vlan 10,20,30

And finally configure uplinks to the network core. Depending on how your LAN core is set up, you may want to create a port channel to the upstream switch and trunk the required VLANs:

# interface range te1/0/1,te2/0/1
# channel-group 2 mode active
# switchport mode trunk
# switchport trunk allowed vlan 10,20,30
# show intefaces po2

Conclusion

This guide didn’t include information on Spanning Tree, QoS or any of the switch Layer 3 features, but I hope it could get you started. At the end of the day, every environment is different. If you need additional information refer to the following guides from the Dell web-site:

 

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2 Responses to “Beginner’s Guide to Dell N4000 Series Switches”

  1. James Williams Says:

    Very useful; many thanks.

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