• Guest shell, Docker containers, and the host Bash Shell use Kernel Stack (kstack).

• The Guest Shell and the host Bash Shell start in the default network namespace. Docker containers start in the management network namespace by default.

  • Other network namespaces may be accessed by using the setns system call

  • The nsenter and ip netns exec utilities can be used to execute within the context of a different network namespace.

• The interface state may be read from /proc/net/dev or retrieved using other typical Linux utilities such as ip , ifconfig , or netstat . The counters are for packets that have initiated or terminated on the switch.

• ethtool –S may be used to get extended statistics from the net devices, which includes packets that are switched through the interface.

• Packet capture applications like tcpdump may be run to capture packets that are initiated from or terminated on the switch.

• There is no support for networking state changes (interface creation or deletion, IP address configuration, MTU change, and so on) from the Guest Shell.

• IPv4 and IPv6 are supported.

• Raw PF_PACKET is supported.

• Only on stack (Netstack or kstack) at a time can use well-known ports (0-15000), regardless of the network namespace.

• There is no IP connectivity between applications using Nestack and applications running kstack on the same switch. This limitation holds true regardless of whether the kstack applications are being run from the host Bash Shell or within a container.

• Applications within the Guest Shell are not allowed to send packets directly over an Ethernet out-of-band channel (EOBC) interface to communicate with the line cards or standby Sup.

• The management interface (mgmt0) is represented as eth1 in the kernel netdevices.

• Use of the VXLAN overlay interface (NVE x) is not supported for applications utilizing the kernel stack. NX-OS features, including CLI commands, are able to use this interface via netstack.

  For more information about the NVE interface, see the Cisco Nexus 9000 Series NX-OS VXLAN Configuration Guide.

Starting with the NX-OS 9.2(2) release, netdevices representing the front channel port interfaces are always in the ADMIN UP state. The final, effective state is determined by the link carrier state.

The following example shows the following interfaces in NX-OS, where eth1/17 is shown as up and eth1/1 is shown as down:

root@kstack-switch# sh int ethernet 1/17 brief
Eth1/17       --      eth  routed up      none                       1000(D) –

root@kstack-switch# sh int ethernet 1/1 brief
Eth1/1        --      eth  routed down    Link not connected         auto(D) –

The following example shows these same interfaces, but this time as shown in the Bash shell using the ip link show command:

bash-4.3# ip link show Eth1-17
49: Eth1-17: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP mode DEFAULT group default qlen 100
    link/ether 00:42:68:58:f8:eb brd ff:ff:ff:ff:ff:ff

bash-4.3# ip link show Eth1-1
33: Eth1-1: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast state DOWN mode DEFAULT group default qlen 100
    link/ether 00:42:68:58:f8:eb brd ff:ff:ff:ff:ff:ff

In this example, Eth1-1 is shown as being UP, but is shown as NO-CARRIER and state DOWN.

The following example shows these same interfaces, but this time as shown in the Bash shell using the ifconfig command:

bash-4.3# ifconfig Eth1-17
Eth1-17   Link encap:Ethernet  HWaddr 00:42:68:58:f8:eb
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:7388 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:100
          RX bytes:0 (0.0 B)  TX bytes:1869164 (1.7 MiB)

bash-4.3# ifconfig Eth1-1
Eth1-1    Link encap:Ethernet  HWaddr 00:42:68:58:f8:eb
          inet addr:99.1.1.1  Bcast:99.1.1.255  Mask:255.255.255.0
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:100
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

The output from the ifconfig command provides different information, where the RUNNING keyword is used to represent the final state. By default, all netdevices show the keyword UP, which represents the ADMIN state of the netdevice in the kernel.

Following are the changes that are part of the NX-OS 9.2(2) release:

• IPv4 address on netdevices — Before the NX-OS 9.2(2) release, the IPv4 address would be plumbed to the netdevice in the kernel even when the corresponding interface in NX-OS was in the DOWN state. Starting with the NX-OS 9.2(2) release, the IPv4 address are plumbed to the kernel space only when the interface is in the UP state. Once plumbed, the IPv4 address continues to stay with the netdevice in the kernel even if the interface goes DOWN. It will be removed only after you have entered the following CLI command to explicitly remove the IP address from the NX-OS interface:

  Interface Eth1/1
              no ip address IP-address
  
  

• IPv6 address on netdevices — Before the NX-OS 9.2(2) release, the IPv6 address would get flushed from the netdevices in the kernel when the interface was DOWN. Starting with the NX-OS 9.2(2) release, the netdevices are always in the admin UP state, so the IPv6 addresses will not get flushed from the kernel when the interface goes down.