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3. The formation of routing tables?

Obtaining routing tables

1)Direct routing: configure IP address, port UP state, form direct routing.

2)Non-directly connected segments: static or dynamic routing is required, adding segments to the routing table

4. What are the characteristics of static routing and dynamic routing? What are some common dynamic routing protocols?

Static routing characteristics: manually configured by the administrator, is unidirectional, and therefore requires dual routing on the edge router between two networks

Square to finger, otherwise it will cause traffic to have no return, lack of flexibility, suitable for small networks.

Dynamic routing is a network of routers communicate with each other, transfer routing information, using the received routing information more

The process of creating a new routing table is based on a routing protocol. Common routing protocol types are: Distance vector routing protocols (such as

RIP) and link-state routing protocols such as OSPF. Routing protocols define rules for routers when communicating with other routers.

5. What is floating routing? What is the default route?

Floating route: Configure a static route with a larger administrative distance as a backup path for emergency triggers. Under the condition that the main route is valid,

Floating routes do not appear in the routing table.

Default route: Default route is a special static route, also known as "default gateway" for the host of the network.

The default routing destination network is 0.0.0.0/0.0.0.0 and can match any destination address only if none is found in the routing table.

The default route is used only if the route entry is correct.

6. How can I access a host without accessing it? What are the specific ideas?

Two hosts can not access between the firewall may be open or two hosts are not in a network segment, is there a correct gateway

address, whether the direct link between host and gateway can ping, whether dns can be resolved normally.

Workaround: Check that the firewall is turned off to see if two hosts are on the same network.

ping gateway whether can pass, use dns to resolve whether the domain name can be resolved normally

What are the protocols at the transport layer? What are the characteristics?

TCP,UDP

TCP: Transmission Control Protocol, reliable, connection-oriented protocol, transmission inefficiency

UDP: User packet protocol unreliable, connectionless service, high transmission efficiency.

2. TCP connections and disconnections?

TCP links through three handshakes, links through four disconnects,

syn: Set this value to 1 when establishing a connection

ACK: ACK=1 indicates acknowledgement,ACK=0 indicates invalid acknowledgement

FIN:FIN=1 indicates disconnection request

3. Please briefly describe the common application layer protocols, what protocols are used at the transport layer, and how many port numbers?

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DNS-TCP or UDP port number 53

HTTP-TCP port number 80

HTTPS-TCP port number 443

SMTP-TCP port number 25

POP3-TCP port number 110

TELNET-TCP port number 23

FTP-TCP port numbers 21 and 20

TFTP-UDP port number 69

Cisco Advanced Routing and Switching (CISCO part)

1. What is Vlan? The role of Vlan? The default switch interface is in which Vlan? What kind of Vlan?

Vlan: Virtual local area network

Effects: Broadcast control, improved security, bandwidth utilization, reduced latency

The default switch interface is in vlan1

Types of vlan: static vlan based on port partition and dynamic vlan based on mac address partition

2. What is Trunk? What are the patterns of Trunk?

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trunk: trunk link, which can carry multiple vlans

Trunk mode:

Access

Trunk

Dynamic Desirable Initiative

Dynamic Auto Passive

3. Differences between ISL and 802.1Q

Same points: both show VLAN information

Difference:

IEEE 802.1Q is a public notation,ISL is Cisco proprietary

ISL uses the external marking method, 802.1Q uses the internal marking method

ISL tags are 30 bytes long and 802.1Q tags are 4 bytes long

4. What is EtherChannel? What does it mean?

Eternet channel (Ethernet channel) function: multiple lines Load Balancer, bandwidth increase, when a line failure, other lines pass

letter, no packet loss.

5. What is DHCP? The role of DHCP?

DHCP: Dynamic Host Configuration Protocol

Role: automatically assign ip addresses to clients

1. What is a Layer 3 Switch? What is the difference between Layer 2 switching and Layer 3 switching and routing?

Layer 3 switches: switches with network layer routing capabilities are called Layer 3 switches

Difference:

Layer 2 switch: belongs to the data link layer equipment, according to the MAC address table to achieve the forwarding of data frames.

Layer 3 switch: Layer 3 switching technology is a technology that combines routing technology and switching technology into one. after routing the first data stream,

It will generate a MAC address and IP address mapping table, when the same data flow through again, will be directly from the second layer according to this table

the method eliminates network delay caused by router route selection and improves the efficiency of data packet forwarding.

Routers: Routers operate at Layer 3 of the OSI Layer 7 protocol, and their primary task is to receive packets from a network interface, according to

The destination address is the address of the destination address.

2. What are the types of routing protocols according to their scope of application?

Routing protocols can be divided into two categories according to the scope of application

1)The routing protocols within an AS are called Interior Gateway Protocols. Interior Gateway Routing Protocols are RIP-1,RIP-2,IGRP,

EIGRP,IS-IS and OSPF.

2) The routing protocol between ASs is called the Exterior Gateway Protocol.

Exterior Gateway Protocol (also known as Interdomain Routing Protocol). There are two types of interdomain routing protocols: Exterior Gateway Protocol (EGP) and Border Gateway Protocol (BGP).

3. What are the types of dynamic routing algorithms? Give examples separately?

Dynamic routing can be divided into distance vector routing protocol and link state routing protocol according to algorithm.

Distance Vector Routing Protocol: Route selection based on the number of routes traversed from the source network to the destination network RIP,IGRP

Link-state routing protocol: routing OSPF,IS-IS, considering all paths from the source network to the destination network

1. What is HSRP? How does it work?

HSRP: Hot Backup Routing Protocol

HSRP is a cisco proprietary protocol that ensures rapid and transparent recovery of user communications when network edge devices or access links fail.

This provides redundant rows for IP networks. By using the same virtual IP address and virtual MAC address, two or more computers on a LAN segment

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A router can serve as a virtual router. HSRP enables cisco routers in a group to monitor each other's health.

2. What is STP? Function?

STP: Spanning Tree Protocol

Function: logically disconnect the loop, prevent the generation of broadcast storm, when the line fails, block the interface is activated, restore communication, and act as a backup line

role.

1. What is ACL?

ACL(Access Control List): Read Layer 3 and Layer 4 packet headers and filter packets according to predefined rules.

2. What is wildcard mask?

Wildcard mask: Also called inversion. The binary numbers 0 and 1 indicate that if a bit is 1, it means that this bit does not need to be matched.

A value of 0 indicates that strict matching is required.

1. What is NAT? What are the ways to do this?

NAT(Network Address Translation): Making an internal network accessible by translating its private IP address into a globally unique public IP address

to connect to external networks such as the Internet.

NAT is implemented in:

Static conversion;IP address correspondence is one-to-one, and is unchanged, with the help of static conversion, can achieve some specific services in the external network

Access to services.

Dynamic translation:IP address mapping is uncertain, but random, all authorized access to the Internet private address can be random

to any specified legitimate external IP address.

Port multiplexing: By changing the source IP address and source port of outgoing packets and performing port translation, all hosts in the internal network can be

Sharing a legal IP address to achieve Internet access, saving IP.

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