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Unlike traditional Catalyst switches running IOS, Nexus switches run NX-OS. There are some similarity between IOS and NX-OS. Also there are new features and commands introduced in NX-OS.
In regards of CLI commands, there are several new commands on Nexus NX-OS image. There are also old commands you find on regular IOS image, and there are modified command compared to the regular IOS. Legacy command such as write memory is not supported anymore, therefore you have to get used to the copy running-config startup-config command.
A nice feature in Nexus switch is that you don't have to exit configuration mode to type in any non-configuration commands. You don't type in the do command when you are on configuration mode to type in any non-configuration commands. You simply type in the non-configuration commands directly whether you are on regular enable mode or configuration mode, similar to PIX Firewall or ASA.
All switch ports in Nexus switches only support 1 Gbps and 10 Gbps speed. Interestingly, these gigabit ports do not show as GigabitEthernet ports or TenGigabitEthernet ports on switch configurations. Instead the ports show as Ethernet interfaces. To find out which speed the ports are acting current, you can simply issue the good old show interface status or simply show interface command.
Along with new commands and features, there are several new concept and technology in place. One new technology found in Nexus switch is FEX (Fabric Extender). Typically you use this FEX technology when you have Nexus 2000 and Nexus 5000 interconnectivity.
This FEX technology is similar to the Catalyst 3750 stacking technology where switch configuration within the same "stack" is visible through just one switch. Similar to Catalyst 3750 stack switch configuration, the Nexus 5000 shows as the "module 1" and the Nexus 2000 shows as the "module 2".
Unlike Catalyst 3750 stack switch, the Nexus do not use stack cable. The switch port to interconnect the two Nexus switches are SFP slot. In order to interconnect the two Nexus switches, the switch ports are configured as FEX ports instead of regular trunk or access ports.
To start using this FEX feature, you have to activate FEX on the Nexus 5000. As you will see, you have to activate telnet and tacacs+ should your network need to use those as well. In other words, there are some features that you have to active when you plan to use the features as part of your Nexus switch network topology.
Further, you have to define how the Nexus 2000 port number should look like. If let's say you configure the FEX port as FEX 101, then all Nexus 2000 switch port will show as interface Ethernet 101 (the "module 2") while the Nexus 5000 switch port show as the regular interface Ethernet 1 (the "module 1").
Note that there is no console port on Nexus 2000. There is console port however on Nexus 5000. Therefore you need to use the FEX technology to interconnect Nexus 2000 and Nexus 5000 in order to have console access to Nexus 2000.
When you need to use the management port on the Nexus 5000 (and also Supervisor 6E of Catalyst 4500 series), make sure you have at least some familiarity with VRF (VPN Routing and Forwarding) technology since these management ports are using involving VRF.
You can't disable the VRF or make the management (mgmt) interface as part of default VRF or global routing table since such action is not supported. The idea of having management port in different routing table is to separate management network and production network, in addition to integrate VRF into Nexus switch platform and new Catalyst 4500 Supervisor Engines.
You will notice that there is a little difference in VRF command implementation between traditional IOS and NX-OS. You can also put in subnet mask in CIDR format, since Nexus platform saves any IP address info in CIDR format.
Unlike traditional Catalyst switches that come with default Layer-2/3 VLAN 1, Nexus 5000 switches only come with default Layer-2 VLAN 1. If you are considering of using non-management switch port as your customized management port, it might not work. Note that Nexus 5000 and 2000 switches are designed as Layer-2 switches originally. The Layer-2 switch design means that you can't create Layer-3 VLAN on Nexus switches as management VLAN (i.e. SVI VLAN interfaces 1, 50, or else) like you usually expect in traditional Catalyst switches. You can't convert any non-management switch port as routing port either. In other words, there is no choice but to use the mgmt port and get used to VRF environment when you are not used to it yet.
Recently the Nexus 5000 switches are now Layer-3 capable though the 2000 model remains Layer-2 switch. You may need to upgrade the NX-OS image and/or upgrade the license on the 5000 model in order to support this Layer-3 functionality.
Some management command like backing up your Nexus configuration to TFTP server (copy running-config tftp: command) is also considering VRF. With copy running-config tftp: command, you will be asked if the TFTP server is located within the default VRF or else (like the management VRF).
Check out the following FAQ for illustrations.
»Cisco Forum FAQ »Sample Configuration: Nexus 5000 and Nexus 2000 with FEX
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