first round ( with hr ) :
what you are doing in your current job
descibe the troubleshooting process you usual use
why you want to leave your crrent job
what is the different between UDP and TCP
what the dhcp process
second round : (review the basic packet route thourgh same vlan or differnt vlan, explain in details)
the senario is the picture , describe the packet when A ping B ?
sine the two hosts are in the same vlan , when A want to send some data to B , it will create an Entehrnet frame which has a source mac address(aaa) and destination mac address (bbb), each applicant has a mac address table , the switch at first just learnt aa from A on the interface 1,and add the information on its mac addess table , then switch flooding the frame out of all its interfaces except the one where it came from, all the devices in the subnet will received the frame,when B received the fram and saw the destination mac address is same as itself, B will response to A, it will build an enthernet frame and send it towards the switch ,switch will learn bbb and forwards the frame to A, switch will add bbb on its interface 2, the switch now know both A and B mac address and can forward the frame now
A,B in different vlans ,how about the packet when A ping B ,fill in the the form of SIP ,DIP ,SMAC and DMAC
when A want to ping B , A will check whether they are in the same subnet, figure out B is in the different subnet, A will use the default gateway , A will build the frame with its own surce mac address , and then check its arp table to see whether the gw's mac in the table , if yes ,just add the gw's mac as the destination mac address. if no, it will send an ARP request which is broadcast packet to ask the mac of its gw, when swtich received the arp request ,it check its mac address table and did not find any result , it will flooding the arp to all the other ports , when the arp request arrive at the router , the gw will reply with its mac address and A will add the mac address on its arp table , then A will encapsulte the frame with
source MAC : A's mac destination MAC : gw of A's mac
source IP : A's IP destination IP : B's IP
when the router receive the frame , figure out the destination mac is match with its mac on the interface , it will de-encapsulate the IP packet out of the frame, the router will now look at the ip packet and the first thing it does is to check the header checksum is ok , if is wrong , will drop the packet, if right , it will continue look at the destination ip address , and check the route table to see if there is a match , since B's deafult gw is also on router , router will have the route to B , route will decrease the TLL by 1 and and check the arp table of its own to see whether there is an entry for the subnet of B, if not , R1 will send an ARP request to find the MAC of B, then R1 will build a new ethernet frame with
source MAC gw of B's mac destination MAC : B's mac
source IP :A's IP destination IP : B's IP
and then forward the frame to B :
B receive the frame and will
check the FCS
find its own mac address as the destinaiton mac address
de-encapsulate the ip packet from the frame, and figure out its own ip is the destinaiton ip
Let’s summarize this process.
The host has a simple decision to make:
Is the destination on the local subnet?
Check ARP table for destination IP address, if empty, send an ARP request.
Is the destination on a remote subnet?
Check ARP table for default gateway IP address, if empty, send an ARP request.
The router has to perform a number of tasks:
When it receives an Ethernet frame, check if the FCS (Frame Check Sequence) is correct. If not, drop the frame.
Check if the destination address of the frame is:
destined to our MAC address
destined to a broadcast address of the subnet our interface is in.
destined to a multicast address that we listen to.
De-encapsulate the IP packet from the frame, discard the Ethernet frame.
Look for a match in the routing table for the destination IP address, figure out what the outgoing interface and optionally, the next hop IP address is.
Decrease the TTL (Time to Live) field in the IP header, recalculate the header checksum.
Encapsulate the IP packet in a new Ethernet frame.
Check the ARP table for the destination IP address or next hop IP address.
Transmit the frame.
C get the ip from the dhcp server , tell about the prcoess
here are 4 type of packets ( Discover, Offer, Request, ACK ie DORA ) exchanged prior to PC get an IP.
when C what to connect to the internet , like connect to goolge.com, what will happened
senario as the right one, describe the process of spanning tree.