1. Write the sequence of twisted pair T568-A and T568-B.
T568-A: white green, green, white orange, blue, white blue, orange, white brown, brown
T568-B: white orange, orange, white green, blue, white blue, white green, green, white brown, brown
2. The correspondence between the OSI seven-layer model and the TCP/IP five-layer model.
| OSI seven-layer model | TCP/IP five-layer model |
|---|---|
| Application layer | Application layer |
| Presentation layer | |
| Session layer | |
| Transport layer | Transport layer |
| Network layer | Network layer |
| Data link layer | Data link layer |
| Physical layer | Physical layer |
3. Data encapsulation and decapsulation process.
Application layer upper layer data (pure data)
Transport layer TCP header + upper layer data
Network layer IP header + TCP header + upper layer data
Data link layer MAC header + LLC header + IP header + TCP header + upper
physical layer Bit stream
Data encapsulation process: top-down, increase the header layer by layer;
data decapsulation process: bottom-up, subtract the header layer by layer.
4. Briefly describe the working principle of ARP
ARP refers to the known target IP location and target MAC.
Example: If PC1 wants to send a message to PC2, but only knows the IP of PC2 and the MAC of PC2, it will send a broadcast frame to the switch through ARP. When the switch receives the broadcast frame, it will perform broadcast processing unconditionally. At this time, it is connected to the switch. All hosts can receive this broadcast frame. They will compare whether their IP is consistent with the target IP. If they are inconsistent, they will discard it. If they are consistent, they will reply to the sender and then report their MAC and IP. , When the sender receives the secondary data, check the receiver's MAC and IP address and put them into the ARP cache table.
5. How many binary digits is the IP address? What are the components?
The IP address is 32 bits = network part + host part
6. How many binary digits is the MAC address? What are the components?
The MAC address is 48 bits = vendor ID + its unique number to the network card
7. What does the subnet mask do?
Function: Divide LAN, distinguished host ID and network ID
8. How does the switch work?
1>Learn based on the source MAC address
2>Based on the known target
3>When the target MAC address is unknown, flood processing
4>When the switch receives a broadcast/multicast frame, unconditional flood processing
5>One interface of the switch can learn multiple MAC address
6> When the switch learns the same MAC address, but learned it from a different port, bind the MAC address to the later learned port at this time
9. How does the router work?
Working principle: 1. Forward the data packet to the correct destination
2. Select the best path during the forwarding process
10. What is the broadcast domain of the switch? What is the router broadcast domain?
Switch broadcast domain: all ports are in a broadcast domain
Router broadcast domain: one broadcast domain per port
11. What are the link types of switch interfaces? What are the characteristics of the access interface? What are the characteristics of the trunk interface?
Switch interface link types are: access, trunk, hybrid
Access. Access interface features: one and only one VLAN
Trunk trunk interface features: can carry multiple VLAN traffic
12. What technology is used to solve the data communication between the same VLAN? What technology is used to solve data communication between different VLANs?
Solve the data communication between the same VLAN: access, trunk, hybrid
data communication between different VLAN: single-arm routing, three-layer exchange
13. What is the default priority of the switch? Rules for electing the root bridge/root switch?
The default switch priority is 32768.
Root switch election rules: Lowest BID = bridge priority + MAC address (the smaller the better)
14. What are the rules for electing root ports and designated ports?
1. Lowest path cost to root bridge (the minimum path cost to the root)
2. Lowest sender BID (the smallest sender BID)
3. Lowest sender port ID (the smallest sender PID)
15. Classification of routing protocols?
In LAN-IGP (Interior Gateway Routing Protocol)
RIP, EIGP Distance Vector Routing Protocol
OSPF, ISIS Link State Routing Protocol
Internet-EGP (External Gateway Routing Protocol-BGP)
16. The command to view the arp cache on the host? Command to clear the arp cache on the host? How to bind arp and mac commands on the host?
The ARP command in the Windows system Huawei devices view ARP
arp -a view ARP cache table arp-static view arp cache
arp -d clear arp cache rest arp static reset static arp
ARP binding arp -s+IP address+MAC address (static Binding)
ARP unbinding arp -d+IP address (static unbinding )
17. What are the criteria for the router to select the optimal route?
1. The highest priority matching with the longest subnet mask length;
2. The highest priority matching with the smallest priority among routing protocols is selected;
3. In the case of the same routing protocol, the highest priority matching with the smallest metric value is selected;
each protocol metric The value definitions are different, and the static routing protocol is related to the routing priority. This is considered to be specified. The RIP protocol is related to the number of hops. The smaller the number of hops, the higher the priority. The OSPF protocol is related to the bandwidth. The larger the bandwidth, the higher the priority. Metric is used to judge the quality of the link.
4. If none of the above routes can be matched, match the default route.
18. The three tables of OSPF?
Neighbor table, link state database, routing table
19. DR and BDR election rules?
Automatic election of DR and BDR: the router with the largest router-ID on the network segment will be elected as the DR, and the second largest will be elected as the BDR;
manual election of DR and BDR: 1. The priority range is 0-255, the larger the value The higher the priority, the default is 1
2. If the priority is the same, you need to compare the Router-ID
3. If the priority of the router is set to 0, it will not participate in the election of DR and BDR.
20. What are the states during the formation of OSPF adjacency relations? What is each state like?
1. Down: The initial state of the neighbor state machine, which means that the HELLO message of the other party has not been received in the past Dead-intervla time.
2. Init: This state indicates that the neighbor's HELLO message has been received, but it is listed in the message My Router-id
3 and 2-way are not included in the out neighbors : This state means that both parties have received HELLO messages from the opposite end and established a neighbor relationship. In broadcast and NBMA type networks, the DRother routers of the two interface states will stay in this state.
4. Exstart: In this state, the router and its neighbors exchange DBD messages (the message does not contain actual content, only some flag bits) to determine the master/slave relationship when sending. The main purpose of establishing the master/slave relationship is to ensure orderly transmission in the subsequent DBD message exchange.
5. Exchange: The router uses DBD messages to describe the local LSDB and sends it to neighbors.
6. Loading: The router sends LSR messages to the neighbors to request the other party's DBD messages.
7. Full: In this state, all the LSAs in the LSDB of the neighboring router are present in the local router. That is, this router has established an adjacency relationship with its neighbors.
21. How many packet types does OSPF have? What is their function?
HELLO package: used to discover and maintain neighbor relationships, elect DR and BDR
database description package DBD: used to send summary information to neighbors to synchronize the link state database
link state request package LSR: the router receives the DBD containing new information Send later to request more detailed information.
Link state update package LSU: Send link state notification LSA after receiving LSR. One LSU packet may contain multiple LSA
link state confirmation packets. LSAck: Confirm the received LSU, Each LSU needs to be confirmed separately
22. How many LSAs does OSPF have? What does each LSA do?
The first type of LSA: router-LSA: generated by each router, describing the link status and cost of the router, and transmitted to the entire area. The
second type of LSA: Network-LSA: generated by the designated router DR, describing the network segment Link status, transmitted to the entire area
Type III LSA: Net-summary LSA: Generated by ABR, describing a certain network segment route in the area, and transmitted to the entire area
Type IV LSA: ASBR summary LSA: Generated by ABR, but it It is a host route that points to the ASBR router address.
Type 5 LSA: Autonomous System External LSA: Generated by ASBR to tell routers in the same autonomous region the path to the outside. The Autonomous Region external LSA is the only LSA that is not associated with a specific area. The announcement will be flooded in the entire autonomous system.
Type 6 LSA: Group member LSA: Currently does not support resistance ratio OSPF (Mospf Protocol)
Type 7 LSA: NSSA External LSA: Generated by ASBR, almost the same as Type 5 LSA notification The same, but the NNSA external LSA notification is only flooded inside the non-pure peripheral area where the NNSA external notification originated
23. The role of virtual roads? Where to use it?
Function: help this non-backbone area to obtain a complete LSDB
use case: a non-backbone area spans another non-backbone area and the backbone area to establish a complete LSDB use
24. Which types of LSAs are blocked by peripheral, complete peripheral, sub-stub, and complete sub-stub? Which router delivers the default route of the complete stub and the complete substub?
Stub and second stub prevent LSA types 4 and 5 from being passed into the stub area.
Completely stub and completely second stub prevent LSAs of type 3, 4, and 5 from being passed into the stub. All stubs and
complete stubs all have ABR to deliver the default router.
25. What kind of protocol does BGP belong to? What is the agreement number?
BGP transmission protocol: TCP protocol; protocol port number: 179
26. Write out the BGP state machine.
There are six types of BGP state machines: Idle state, Connect state, Active state, Opensent state, OpenConfirm state, and Establish state.
27. BGP routing principle? Which BGP attributes can generally be modified during IBGP neighbor routing? Which BGP attributes can generally be modified during EBGP neighbor routing?
1. If the next hop of the route to the destination network is not selectable, you can ignore this route.
2. The route with the higher Preferred-value priority takes precedence.
3. The router with the higher Local-Preference priority takes precedence (default 100)
4. The priority of aggregated routes is higher than that of non-aggregated routes.
5. The priority of local manually aggregated routes is higher than that of local automatically aggregated routes.
6. The priority of local routes imported through the Network command is higher than that of local routes imported through the Import-route command.
7. The path with the shortest AS path length (the number of groups is small) has a higher priority
8. Compare the origin attribute, the IGP priority is higher than EGP, and the EGP priority is higher than Incomplete
9. Choose the route with the smaller MED priority (default is 0 )
10, the routing priority than the EBGP IBGP routes
. 11, to a low preference BGP BGP next hop path IGP metric
when the above are all the same, for the oRDER route, load balancing (Note: aS-pATH must be the same) When load sharing, the following three principles are invalid.
12. Compare the length of the Cluster-list. The shorter one takes precedence.
13. Compare the Originator-ID (if there is no originator-id, use the Router-ID to compare). Choose the path with the smaller value.
14. Compare the right path . Equivalent IP address, choose the path with the smallest IP address value
28. What are the router roles in vrrp? How does it work?
VRRP router role: main route, backup route, virtual route
Working principle: if the terminal sends data packets to the MAC address of the virtual router, the main router will receive and process these data packets, if the terminal sends an ARP request containing the virtual router IP address , The main router responds with the MAC address of the virtual router. When the main router fails, other vrrp routers will stop receiving hello messages, and the backup router will take over the data forwarding work of the main router. At the same time, the IP address and MAC address of the virtual router will be assigned to the new main router.
29. The role of nat? How does it work? When is it used?
The role of NAT: network address conversion, IPV4 network address cannot be done by one person, so it needs to use network address translation to convert the autonomy of the internal network into a public network address, so that LAN terminals can access the Internet.
Working mode: Static NAT: One dead IP address corresponds to one public IP address
Dynamic NAT: Multiple private IP addresses correspond to multiple public IP addresses
PAT: Multiple private IP addresses correspond to one public IP address,
static PAT: One-to-one, external network mapping internal network service
30. Where is acl used? What kinds of acl are divided into? What are their list numbers? What should I pay attention to when using these types of ACLs?
ACL use occasions: used to control access to data packets (discard or pass), combined with other protocols, used to match the range
ACL type: standard list (2000-2999): only match the source IP address
extended list (3000-3999) : Can match the source IP, destination IP, source port, destination port layer 3 and 4 fields
Layer 2 acl (4000-4999): According to the source MAC address, destination MAC address, 802.1Q priority, second Rules for setting up layer 2 information such as layer protocol type
31. The difference between TCP and UDP protocol?
TCP: Divide the message into smaller segments, called data segments; data segments are numbered sequentially; if the sender does not receive the confirmation within the specified time, it will consider the data segment to be lost and resend it.
UDP: does not require confirmation to receive, is the most efficient transmission mechanism; no confirmation and retransmission mechanism; it is the first choice for applications such as audio streaming, video streaming and Voice over IP (VoLP)
32. Briefly describe the three-way handshake and four-time disconnection of TCP.
Three-way handshake: 1. The sender sends a SYN request
to the receiver. 2. The receiver will actively reply an ACK after receiving this request and send a SYN request at the same time.
3. After the sender receives the SYN request from the receiver, it will give An ACK confirmation
Four disconnections: 1. The sender sends a FIN request to the
receiver. 2. The receiver gives an ACK confirmation after receiving this request.
3. The receiver sends a FIN request to the sender.
4. The sender receives the reception. Recover an ACK after the party’s FIN request
