DHCP

 DHCP Questions:

DHCP server within the subnet

                DHCP Discover(Broad cast)

client  -----------------------------> server

              DHCP offer(unicast/ Broadcast)

client  <----------------------------- server

        DHCP Request(Broad cast)

client  -----------------------------> server

     DHCP ACK(Broad cast/ Unicast)

client  <----------------------------- server

Got the IP.

2) DHCP server outof the subnet, DHCP proxy and relay:

When the server is out of subnet, The router acts as relay agent with its b'wn the client and server.

client sends broadcast packet to router, The router configured as relay agent forwards the packet convert ing the broadcast packet to unicast packet.

The relay agent includes its own IP address in the Gateway IP address field to let know the server in which subnet client  is located to assign an IP address.

The DHCP server sends back/forwards the offer packet to the relay agent with the offered address from the subnet based on gateway address field.

The relay agent receives the server's unicast DHCPOFFER and forwards it back to the original client via broadcast

The client then sends a DHCPREQUEST message as Braodcast msg through the relay agent. 

The server responds with a DHCPACK, confirming the assignment of the IP address.

The relay agent forwards these messages between the client and server as necessary

DHCP client renews lease time when expires

DHCP options.

DHCP port numbers.

68

 structure padding and packing:

Structure is of user defined data types, Could be with the different combination of data types. When structure is defined with different data types, this data types aligned with padding to its natural boudaries of data, to reduce the CPU cycles.

struct sample {

char a;

char b;

int c;

}

If structure padding is not there to read an int variable it takes 2 CPU cycles, where as with structure padding it takes a single cycle.

cloudfare:

Is the world wide cloud reverse proxy, which helps in hiding the webservers IP from the web browser. 

In b'wn the webserver and web browser and hides the webservers IP addresses. Hence the DoS attacks can be avoided at the webserver. With somehow at the reverse proxy the DosAttacks are avoided.

SRIOV: 

https://www.lynx.com/embedded-systems-learning-center/what-is-sr-iov-and-why-is-it-important-for-embedded-devices 

SRIOV:  Single Root IO virtualization is a hardware feature where the PCIe (NIC) represented as a Virtaul PCI devices or NIC'c for hypervisor.

How to configure the SRIOV.

How to create the VM's

Packet flow NIC to VM?

Hypervisor:

Hypervisor is a Software which creates multiple VM's and runs the VM's over single hardware unit by sharing the hardware resources.

A hypervisor allows one host computer to support multiple guest VMs by virtually sharing its resources, such as memory and processing. 

Types of Hypervisor:

Type1: Bare metal Hypervisor. Runs on Hardware

Type2: Runs on OS. Hosted Hypervisors. Runs on OS.