Explanation
VXLAN has a 24-bit VXLAN network identifier (VNI), which allows for up to 16 million (= 224) VXLAN segments to coexist within the same infrastructure. This surely solve the small number of traditional VLANs.

Explanation
MACsec, defined in 802.1AE, provides MAC-layer encryption over wired networks by using out-ofband methods for encryption keying. The MACsec Key Agreement (MKA) Protocol provides the required session keys and manages the required encryption keys. MKA and MACsec are implemented after successful authentication using the 802.1x Extensible Authentication Protocol (EAP-TLS) or Pre Shared Key (PSK) framework.
A switch using MACsec accepts either MACsec or non-MACsec frames, depending on the policy associated with the MKA peer. MACsec frames are encrypted and protected with an integrity check value (ICV). When the switch receives frames from the MKA peer, it decrypts them and calculates the correct ICV by using session keys provided by MKA. The switch compares that ICV to the ICV within the frame. If they are not identical, the frame is dropped. The switch also encrypts and adds an ICV to any frames sent over the secured port (the access point used to provide the secure MAC service to a MKA peer) using the current session key.
Reference: https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst9300/software/release/1
6-9/configuration_guide/sec/b_169_sec_9300_cg/macsec_encryption.html
Note: Cisco Trustsec is the solution which includes MACsec.

Explanation
An EEM policy is an entity that defines an event and the actions to be taken when that event occurs. There are two types of EEM policies: an applet or a script. An applet is a simple form of policy that is defined within the CLI configuration. answer 'event manager applet ondemand event register action 1.0 syslog priority critical msg 'This is a message from ondemand'
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There are two ways to manually run an EEM policy. EEM usually schedules and runs policies on the basis of an event specification that is contained within the policy itself. The event none command allows EEM to identify an EEM policy that can be manually triggered. To run the policy, use either the action policy command in applet configuration mode or the event manager run command in privileged EXEC mode.
Reference: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/eem/configuration/xe-3s/eem-xe-
3s-book/eem-policy-cli.html

Explanation
The BGP session may report in the following states
1 - Idle: the initial state of a BGP connection. In this state, the BGP speaker is waiting for a BGP start event, generally either the establishment of a TCP connection or the re-establishment of a previous connection. Once the connection is established, BGP moves to the next state.
2 - Connect: In this state, BGP is waiting for the TCP connection to be formed. If the TCP connection completes, BGP will move to the Open Sent stage; if the connection cannot complete, BGP goes to Active
3 - Active: In the Active state, the BGP speaker is attempting to initiate a TCP session with the BGP speaker it wants to peer with. If this can be done, the BGP state goes to Open Sent state.
4 - Open Sent: the BGP speaker is waiting to receive an OPEN message from the remote BGP speaker
5 - Open Confirm: Once the BGP speaker receives the OPEN message and no error is detected, the BGP speaker sends a KEEPALIVE message to the remote BGP speaker
6 - Established: All of the neighbor negotiations are complete. You will see a number, which tells us the number of prefixes the router has received from a neighbor or peer group.