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1. Network Interface Management: The Foundation of Network Connectivity

1.1 Analysis of Modern Network Toolchains

In contemporary Linux systems, the <span>iproute2</span> suite has completely replaced the traditional <span>net-tools</span>, with advantages including:

Recommended Command Combinations:

ip -c addr show | grep "inet "  # Display valid IPs in color
ip -br link show                # Show interface status in brief mode
ethtool ens33 | grep Speed      # Check negotiated speed of the network card

Classic Comparison Cases:

# Traditional Method (Not Recommended)
ifconfig ens33 down && ifconfig ens33 up

# Modern Method (Recommended)
ip link set ens33 down && ip link set ens33 up

Core Differences:

• • Supports network namespace isolation
• • Integrates advanced features like VLAN/VXLAN
• • Precise control over ARP cache
• • Full support for IPv6

1.2 Advanced Control of Network Interface Status

In-Depth Operation Examples:

# Check hardware queue status
ethtool -l ens33

# Adjust MTU value (ensure device supports it)
ip link set mtu 9000 dev ens33

# Real-time monitoring of network card status changes
watch -n1 'ip -s link show ens33'

Error Troubleshooting Guide:

1. 1. Check physical layer status: <span>ip link</span> shows <span>LOWER_UP</span> indicator
2. 2. Verify driver loading: <span>lsmod | grep e1000</span>
3. 3. Diagnose DMA configuration: <span>dmesg | grep DMA</span>

1.3 IP Address Configuration Practical Engineering

Dynamic/Static Configuration Comparison Matrix:

Parameter	DHCP Dynamic Acquisition	Static Configuration
Applicable Scenarios	Development Testing Environment	Production Server
Fault Recovery	Automatic Renewal	Manual Maintenance Required
Address Conflict Risk	Higher	Controllable
Management Complexity	Low	High

Multi-IP Binding Practical Example:

# Add auxiliary IP
ip addr add 192.168.1.100/24 dev ens33 label ens33:1

# Persistent configuration
echo 'IPADDR1=192.168.1.100' >> /etc/sysconfig/network-scripts/ifcfg-ens33
echo 'PREFIX1=24' >> /etc/sysconfig/network-scripts/ifcfg-ens33

2. Port Management: Ensuring Service Accessibility

2.1 In-Depth Port Scanning Techniques

Comprehensive Scanning Solutions:

# Quick TCP Scan
nmap -T4 -p 1-65535 127.0.0.1

# UDP Service Discovery
nmap -sU -p 53,67,68,161 localhost

# Stealth Scanning Mode
nmap -sS -Pn -n --disable-arp-ping 192.168.1.10

Connection Status Analysis:

• • TIME_WAIT: Normal closure residue
• • CLOSE_WAIT: Application did not handle closure correctly
• • SYN_RECV: Potential SYN Flood attack

2.2 Firewall Policy Essentials

Advanced Firewalld Configuration:

# Create a custom zone
firewall-cmd --permanent --new-zone=app_zone

# Bind source address range
firewall-cmd --zone=app_zone --add-source=10.0.0.0/24

# Set port forwarding
firewall-cmd --add-forward-port=port=80:proto=tcp:toport=8080

iptables Rule Optimization:

# Connection state tracking optimization
iptables -A INPUT -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT

# Rate limiting protection
iptables -A INPUT -p tcp --dport 22 -m limit --limit 5/min -j ACCEPT

3. Routing Management: Building Intelligent Traffic Paths

3.1 In-Depth Analysis of Routing Tables

Policy Routing Practice:

# Create a custom routing table
echo "200 custom" >> /etc/iproute2/rt_tables

# Add policy rules
ip rule add from 192.168.2.0/24 lookup custom

# Configure multipath routing
ip route add default scope global \
  nexthop via 192.168.1.1 weight 1 \
  nexthop via 192.168.2.1 weight 2

Routing Cache Monitoring:

# Real-time view of routing cache
ip route show cached

# Clear specific routing cache
ip route flush cache 192.168.1.0/24

3.2 BGP Routing Integration

Quagga Configuration Example:

router bgp 65001
 neighbor 192.168.100.1 remote-as 65002
 network 10.0.0.0/8
!
 address-family ipv6
  network 2001:db8::/32
 exit-address-family

4. Network Diagnostics: Full-Stack Troubleshooting Methodology

4.1 Layered Diagnostic Model

+-----------------------+
|    Application Layer (HTTP)      |
+-----------------------+
|    Transport Layer (TCP/UDP)   |
+-----------------------+
|    Network Layer (IP/ICMP)   |
+-----------------------+
| Data Link Layer (ARP/MAC)  |
+-----------------------+
|    Physical Layer (Cables)      |
+-----------------------+

Layered Diagnostic Toolchain:

• • Physical Layer: <span>ethtool</span>, <span>mii-tool</span>
• • Data Link Layer: <span>arping</span>, <span>tcpdump</span>
• • Network Layer: <span>mtr</span>, <span>tracepath</span>
• • Transport Layer: <span>tcptraceroute</span>, <span>socat</span>
• • Application Layer: <span>curl</span>, <span>wget</span>, <span>openssl s_client</span>

4.2 Advanced Diagnostic Techniques

TCP Stream Analysis:

# Capture HTTP traffic
tcpdump -i ens33 -nn -s0 -w http.pcap 'tcp port 80'

# Analyze TLS handshake process
openssl s_client -connect example.com:443 -msg

Performance Bottleneck Identification:

# Measure network throughput
iperf3 -c 192.168.1.100 -t 30

# Count TCP retransmission rate
nstat -az TcpRetransSegs

# Check buffer settings
sysctl net.ipv4.tcp_rmem

5. Network Optimization: Best Practices for Production Environments

5.1 Kernel Parameter Tuning

# Improve TIME-WAIT recycling speed
echo "net.ipv4.tcp_tw_recycle = 1" >> /etc/sysctl.conf

# Optimize TCP window size
echo "net.core.rmem_max = 16777216" >> /etc/sysctl.conf
echo "net.core.wmem_max = 16777216" >> /etc/sysctl.conf

# Accelerate ARP cache updates
echo "net.ipv4.neigh.default.gc_stale_time = 120" >> /etc/sysctl.conf

5.2 Traffic Shaping Solutions

# Create HTB queue
tc qdisc add dev ens33 root handle 1: htb default 30

# Set bandwidth limit
tc class add dev ens33 parent 1: classid 1:1 htb rate 100mbit

# Apply filters
tc filter add dev ens33 protocol ip parent 1:0 prio 1 u32 \
  match ip dport 80 0xffff flowid 1:1

6. New Paradigms in Cloud-Native Networking

6.1 CNI Plugin Practices

Calico Network Configuration:

apiVersion: projectcalico.org/v3
kind: IPPool
metadata:
  name: ippool-1
spec:
  cidr: 192.168.0.0/16
  ipipMode: Always
  natOutgoing: true

6.2 eBPF Network Observability

# Trace TCP connection establishment
bpftrace -e 'tracepoint:tcp:tcp_retransmit_skb { @[args->saddr, args->daddr] = count(); }'

# Count network interrupts
bpftrace -e 'kprobe:__netif_receive_skb { @[kstack] = count(); }'

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