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Skillsdns

dns

Deployment & operations

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Updated 10-15 17:33

About this skill

DNS Configuration and Troubleshooting

Overview

Skills such as DNS configuration, resolution troubleshooting, BIND/CoreDNS, etc.

DNS Query Tools

dig

# 基础查询
dig example.com
dig example.com A
dig example.com AAAA
dig example.com MX
dig example.com NS
dig example.com TXT
dig example.com ANY
Short output

dig +short example.com

Specify DNS server

dig @8.8.8.8 example.com dig @1.1.1.1 example.com

Trace resolution process

dig +trace example.com

Reverse resolution

dig -x 8.8.8.8

Query specific records

dig example.com SOA dig example.com CNAME

Disable recursion

dig +norecurse example.com


### nslookup
```bash
# 基础查询
nslookup example.com
nslookup example.com 8.8.8.8

# 查询特定类型
nslookup -type=mx example.com
nslookup -type=ns example.com
nslookup -type=txt example.com

# 反向解析
nslookup 8.8.8.8

host

# 基础查询
host example.com
host -t mx example.com
host -t ns example.com

# 反向解析
host 8.8.8.8

# 详细输出
host -v example.com

Local DNS configuration

/etc/resolv.conf

# 查看配置
cat /etc/resolv.conf

# 配置示例
nameserver 8.8.8.8
nameserver 8.8.4.4
search example.com
options timeout:2 attempts:3

# 临时修改（可能被覆盖）
echo "nameserver 8.8.8.8" > /etc/resolv.conf

/etc/hosts

# 查看
cat /etc/hosts

# 添加记录
echo "192.168.1.100 myserver.local" >> /etc/hosts

# 格式
127.0.0.1       localhost
192.168.1.100   myserver myserver.local

systemd-resolved

# 查看状态
systemd-resolve --status
resolvectl status

# 查询
resolvectl query example.com

# 刷新缓存
systemd-resolve --flush-caches
resolvectl flush-caches

# 配置文件
/etc/systemd/resolved.conf

BIND DNS Server

Installation and Management

# 安装
apt install bind9 bind9utils          # Debian/Ubuntu
yum install bind bind-utils           # CentOS/RHEL

# 服务管理
systemctl start named
systemctl enable named
systemctl status named

# 检查配置
named-checkconf
named-checkzone example.com /etc/bind/zones/db.example.com

Main configuration

# /etc/bind/named.conf.options
options {
    directory "/var/cache/bind";
    
    forwarders {
        8.8.8.8;
        8.8.4.4;
    };
    
    dnssec-validation auto;
    
    listen-on { any; };
    listen-on-v6 { any; };
    
    allow-query { any; };
    allow-recursion { 192.168.0.0/16; 10.0.0.0/8; };
    
    recursion yes;
};

Zone configuration

# /etc/bind/named.conf.local
zone "example.com" {
    type master;
    file "/etc/bind/zones/db.example.com";
    allow-transfer { 192.168.1.2; };
};

zone "1.168.192.in-addr.arpa" {
    type master;
    file "/etc/bind/zones/db.192.168.1";
};

Zone file

# /etc/bind/zones/db.example.com
$TTL    604800
@       IN      SOA     ns1.example.com. admin.example.com. (
                        2024011501      ; Serial
                        604800          ; Refresh
                        86400           ; Retry
                        2419200         ; Expire
                        604800 )        ; Negative Cache TTL

; Name servers
@       IN      NS      ns1.example.com.
@       IN      NS      ns2.example.com.

; A records
@       IN      A       192.168.1.10
ns1     IN      A       192.168.1.1
ns2     IN      A       192.168.1.2
www     IN      A       192.168.1.10
mail    IN      A       192.168.1.20

; CNAME records
ftp     IN      CNAME   www.example.com.

; MX records
@       IN      MX      10 mail.example.com.

CoreDNS

Configuration file

# Corefile
.:53 {
    forward . 8.8.8.8 8.8.4.4
    cache 30
    log
    errors
}

example.com:53 {
    file /etc/coredns/db.example.com
    log
    errors
}

Kubernetes CoreDNS

# ConfigMap
apiVersion: v1
kind: ConfigMap
metadata:
  name: coredns
  namespace: kube-system
data:
  Corefile: |
    .:53 {
        errors
        health {
            lameduck 5s
        }
        ready
        kubernetes cluster.local in-addr.arpa ip6.arpa {
            pods insecure
            fallthrough in-addr.arpa ip6.arpa
            ttl 30
        }
        prometheus :9153
        forward . /etc/resolv.conf {
            max_concurrent 1000
        }
        cache 30
        loop
        reload
        loadbalance
    }

Common Scenarios

Scenario 1: DNS resolution troubleshooting

# 1. 检查本地配置
cat /etc/resolv.conf

# 2. 测试 DNS 服务器连通性
ping 8.8.8.8

# 3. 查询解析
dig example.com
dig @8.8.8.8 example.com

# 4. 追踪解析路径
dig +trace example.com

# 5. 检查 DNS 缓存
systemd-resolve --statistics

Scenario 2: Clear DNS cache

# systemd-resolved
systemd-resolve --flush-caches

# nscd
systemctl restart nscd

# dnsmasq
systemctl restart dnsmasq

# BIND
rndc flush

# macOS
sudo dscacheutil -flushcache
sudo killall -HUP mDNSResponder

Scenario 3: Test DNS performance

# 使用 dig 测试响应时间
dig example.com | grep "Query time"

# 批量测试
for i in {1..10}; do
    dig +noall +stats example.com | grep "Query time"
done

# 使用 dnsperf
dnsperf -s 8.8.8.8 -d queries.txt

Scenario 4: Configure internal DNS

# 添加内部域名解析
# /etc/hosts
192.168.1.100   app.internal
192.168.1.101   db.internal

# 或配置 dnsmasq
# /etc/dnsmasq.conf
address=/internal/192.168.1.100
server=8.8.8.8

Troubleshooting

Problem Troubleshooting method
Resolution failure Check resolv.conf, DNS server
Slow resolution Check DNS server response, network latency
Cache issues Clear local cache, check TTL
Record does not exist Check zone file, SOA serial number 
# 检查 DNS 端口
ss -ulnp | grep :53
netstat -ulnp | grep :53

# 测试 TCP/UDP
dig +tcp example.com
dig +notcp example.com

# 检查 BIND 日志
tail -f /var/log/named/query.log
journalctl -u named -f