1, small business and large enterprise network network network What is the difference
Small business networks are generally not hierarchical, large enterprise network hierarchy
Small Business Network: easy maintenance, reliability is not strong, the replacement of equipment (switches, routers) easy
Large enterprise networks: reliability, stable, flat design, not easy to replace equipment
2, the basic idea of large-scale enterprise network design
Stability (redundancy), scalability, security (firewall, intrusion detection loading), a plurality of service providers to purchase services, flat, easy to replace apparatus
3, the composition and structure of the network
Terminal equipment: PC, iphone, ATM cash machine, bus card charging terminal, car navigation
Networking equipment: hubs, switches, routers, firewall, IDS, IPS, AP
A link connecting the device \ media: coaxial cable (coarse and fine), an optical fiber (single mode, multi-mode), twisted pair, radio
4. Please describe osi seven layer model, and a brief summary of the function of each layer
Physical layer : bit-stream transmission
Hub (CSMA / CD avoid conflicts)
Data Link Layer : control data transmission frame on a physical link, encapsulated into a data frame, the MAC header, identify the upper layer protocol type
0x0800IP 0x0806ARP
Switcher: dividing collision domain interfaces, one interface is a broadcast domain, MAC address based on the identification, to complete the package and forwarding data frames function of the network device
Ethernet, PPP works in the data link layer protocol
Network Layer : IP addressing and routing, encapsulated into data packets, the IP header, identify the upper layer protocol Protoco
Router: Interface split broadcast domains
IP protocol
ARP protocol (ARP proxy, free ARP): ARP Request ARP cache table → → → ARP cache table in response to ARP
ICMP protocol (transmission error between network devices, control messages): but the transport layer encapsulation is defined as a network layer protocol
Transport Layer : establishment, maintenance, management of end connection, encapsulated into data segments, TCP \ UDP header
Confirmed the role flag in the TCP header: ack 1 indicates the next expected byte received ACK number is valid
TCP: Transmission Control Protocol 0x06
UDP: User Datagram Protocol 0x17
Session layer : the establishment, maintenance, management session connection, higher data
Presentation Layer : data formatting, encryption, decryption
Application Layer : provides network services for applications
File transfer (FTP, TFTP), email (SMTP), remote login (telnet), name management (DNS) Network Management (SNMP)
5, please describe tcp \ ip model, and a brief description of each layer function
Hierarchical model : network interface layer, Internet layer, host-to-host layer, application layer
Peer model :
Physical Layer
data link layer
Network layer
Transport Layer
Application layer
6, ping using which types of icmp messages
echo reply（0）和echo request（8）
7, FCS what action
FCS is used to verify the integrity of a frame during transmission, when the received frame is calculated FCS, and the FCS received if mismatched, the frame
8, the network communication protocol model
OSI, TCP / IP, IPX / SPX, SNA (different protocol stacks to define and manage data of different network forwarding rules)
9. What is the domain of conflict
Collision domain refers to the minimum range will conflict, the computer and the computer via the device network, establishes a channel, if this channel is only allowed instantaneous data packets (shared network), then at the same time if there are two one or more data packets think there will be a signal collision phenomenon through from here
10, how to distinguish Ethernrt_II frame and IEEE802.3 frame
Length / Type> = 1536 (0x0600) is Ethernrt_II frame (type0x0800 the IP protocol, 0x0806 is the ARP protocol)
Length / Type <= 1500 (0x05DC) as IEEE802.3 frame
11, how the switch receives the data frame processing
View source MAC address, is compared with the MAC address table (CAM), look passive MAC address entries
are: see if the MAC entry into the binding interface and the interface to the same
same: refresh timer (300s), searches for the destination MAC
is not same: to rebind interface refresh timer, looks up the destination MAC address
no: MAC address learning and bind directly into the interface, refresh timer, searches for the destination MAC
looks up the destination MAC address
are: Check the destination MAC binding interface into the interface is same (same out again indicates the interface from this interface away from this)
the same: to discard
different: forwarding
no: flooding (all other data transmitted from the external interfaces into other interface)
12, how the terminal device receives a data frame processing
If the data frame destination MAC address is a broadcast address or a multicast address listening, the receiver further processing;
if the destination MAC address is not a broadcast data frame address is not a multicast listener, while not own MAC address are discarded;
if the destination MAC address of the data frame is its own MAC address, the receiver, and using the FCS field of the frame end verify, the data frame is referred to the complete upper layer protocol, if it is incomplete were other ways
13. What is the role of the IP header TTL field is
For avoiding network congestion caused by the loop, the initial TTL value set by the source device, a packet passes through a three-tier equipment, each TTL value minus one, is discarded reduced to zero
If there is a loop network, IP packets may be circulating on the network could not reach the destination. Defining a time to live TTL field of the IP packet, the destination can not be reached to ensure the packets eventually discarded
14, the circumstances under which the network device sends ARP request
Network devices before transmitting data, looks into its ARP cache table, if the mapping relation, the direct use of the package, which did not exist, sending ARP request
15, will have free ARP circumstances under which the network equipment
Free ARP: IP address is not used to detect conflicts
when the device sends gratuitous ARP when the new configuration IP address or change the IP address
16, when the network device receives IP packets with a TTL value of 0, how the operation
When the TTL value is 0, the network device will discard the packet, send a message to the source device TTL-expired