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1. 하드웨어 상태 점검
1.1 물리적 연결 확인
- 모든 케이블이 제대로 연결되었는지 확인
- 네트워크 인터페이스 카드(NIC)의 LED가 정상적으로 깜박이는지 확인
- 케이블에 손상이 의심된다면 교체 추천
1.2 링크 상태 확인
- 링크가 감지되었는지, 속도 및 듀플렉스 설정이 올바른지 확인합니다.
# ethtool eth0
Settings for eth0:
Supported ports: [ TP ]
Supported link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
1000baseT/Full
Supported pause frame use: No
Supports auto-negotiation: Yes
Supported FEC modes: Not reported
Advertised link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
1000baseT/Full
Advertised pause frame use: No
Advertised auto-negotiation: Yes
Advertised FEC modes: Not reported
Speed: 1000Mb/s
Duplex: Full
Auto-negotiation: on
Port: Twisted Pair
PHYAD: 1
Transceiver: internal
MDI-X: on (auto)
Supports Wake-on: pumbg
Wake-on: g
Current message level: 0x00000007 (7)
drv probe link
Link detected: yes- 링크가 활성 상태인지 확인합니다.
# mii-tool eth0
eth0: negotiated 1000baseT-FD flow-control, link ok
2. 시스템 수준 진단
2.1 네트워크 인터페이스 확인
- 활성 인터페이스에 IP 주소가 설정되어 있는지 확인합니다.
- 출력에서 오류, 드롭된 패킷, 충돌 여부를 확인합니다.
# ifconfig -a
docker0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 172.17.0.1 netmask 255.255.0.0 broadcast 172.17.255.255
inet6 fe80::42:21ff:fe87:aeb prefixlen 64 scopeid 0x20<link>
ether 02:42:21:87:0a:eb txqueuelen 0 (Ethernet)
RX packets 0 bytes 0 (0.0 B)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 36 bytes 5955 (5.8 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.207.10 netmask 255.255.255.0 broadcast 192.168.207.255
inet6 fe80::460e:904b:d395:cb6a prefixlen 64 scopeid 0x20<link>
ether d0:50:99:a5:82:33 txqueuelen 1000 (Ethernet)
RX packets 112763656 bytes 64222745390 (59.8 GiB)
RX errors 3 dropped 421 overruns 0 frame 2
TX packets 65293795 bytes 29591807775 (27.5 GiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
device interrupt 20 memory 0xf3100000-f3120000
또는
# ip addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
valid_lft forever preferred_lft forever
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
link/ether d0:50:99:a5:82:33 brd ff:ff:ff:ff:ff:ff
altname enp0s25
inet 192.168.207.10/24 brd 192.168.207.255 scope global noprefixroute eth0
valid_lft forever preferred_lft forever
inet6 fe80::460e:904b:d395:cb6a/64 scope link noprefixroute
valid_lft forever preferred_lft forever
3: docker0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default
link/ether 02:42:21:87:0a:eb brd ff:ff:ff:ff:ff:ff
inet 172.17.0.1/16 brd 172.17.255.255 scope global docker0
valid_lft forever preferred_lft forever
inet6 fe80::42:21ff:fe87:aeb/64 scope link
valid_lft forever preferred_lft forever
5: veth296af2e@if4: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue master docker0 state UP group default
link/ether 7e:62:f2:e3:04:92 brd ff:ff:ff:ff:ff:ff link-netnsid 0
inet6 fe80::7c62:f2ff:fee3:492/64 scope link
valid_lft forever preferred_lft forever
2.2 네트워크 서비스 재시작
# systemctl restart network
# systemctl restart NetworkManager
3. 연결 테스트
3.1 Ping Test
- 물리적으로 연결되어 있는 서버 혹은 게이트웨이 등 에 Ping Test를 한다.
- 외부망이 연결되어 있다면 ping 8.8.8.8 혹의 ping google.com으로 Ping Test 한다.
# ping 192.168.207.11
# ping 192.168.207.2543.2 경로 추적
- 원격 호스트로 가는 경로 확인
# traceroute 192.168.207.254
traceroute to 192.168.207.254 (192.168.207.254), 30 hops max, 60 byte packets
1 * * *
2 * * *
3 * * *
4 * * *
5 * * *
6 * * *
7 * * *
# tracepath 192.168.207.254
1?: [LOCALHOST] pmtu 1500
1: no reply
2: no reply
3: no reply
4: no reply
5: no reply
4. 포트 및 서비스 점검
4.1 Listening 포트 확인
- 프로세스와 함께 TCP Listening 포트를 확인합니다.
# netstat -tlp
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name
tcp 0 0 localhost:radan-http 0.0.0.0:* LISTEN 1240/influxd
tcp 0 0 Master10:origo-native 0.0.0.0:* LISTEN 1250/etcd
4.2 열린 포트 확인
# netstat -ntlp
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name
tcp 0 0 127.0.0.1:8088 0.0.0.0:* LISTEN 1240/influxd
tcp 0 0 192.168.207.10:3001 0.0.0.0:* LISTEN 1250/etcd
tcp 0 0 0.0.0.0:60889 0.0.0.0:* LISTEN 1245/rpc.statd
tcp 0 0 0.0.0.0:40187 0.0.0.0:* LISTEN -
4.3 서비스별 테스트
# curl -I localhost
HTTP/1.1 200 OK
Date: Wed, 22 Jan 2025 00:59:12 GMT
Server: Apache
Set-Cookie: PHPSESSID=heo4pem5fvpiaqvb868kkkn5c6; path=/
Expires: Thu, 19 Nov 1981 08:52:00 GMT
Cache-Control: no-store, no-cache, must-revalidate
Pragma: no-cache
Set-Cookie: PHPSESSID=heo4pem5fvpiaqvb868kkkn5c6; path=/
Set-Cookie: PHPSESSID=heo4pem5fvpiaqvb868kkkn5c6; path=/
Content-Type: text/html; charset=UTF-8
# nslookup naver.com
Server: 8.8.8.8
Address: 8.8.8.8#53
Non-authoritative answer:
Name: naver.com
Address: 223.130.200.219
Name: naver.com
Address: 223.130.192.248
Name: naver.com
Address: 223.130.200.236
Name: naver.com
Address: 223.130.192.247
# dig naver.com
; <<>> DiG 9.11.36-RedHat-9.11.36-14.el8_10 <<>> naver.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 15465
;; flags: qr rd ra; QUERY: 1, ANSWER: 4, AUTHORITY: 0, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 512
;; QUESTION SECTION:
;naver.com. IN A
;; ANSWER SECTION:
naver.com. 43 IN A 223.130.192.247
naver.com. 43 IN A 223.130.192.248
naver.com. 43 IN A 223.130.200.219
naver.com. 43 IN A 223.130.200.236
;; Query time: 37 msec
;; SERVER: 8.8.8.8#53(8.8.8.8)
;; WHEN: Wed Jan 22 10:00:06 KST 2025
;; MSG SIZE rcvd: 102
5. 라우팅 진단
5.1 라우팅 테이블 확인
# route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
0.0.0.0 192.168.207.250 0.0.0.0 UG 100 0 0 eth0
172.17.0.0 0.0.0.0 255.255.0.0 U 0 0 0 docker0
192.168.207.0 0.0.0.0 255.255.255.0 U 100 0 0 eth0
6. ARP 테이블 점검
6.1 ARP 엔트리 확인
# arp -a
? (192.168.207.254) at 00:25:90:94:0c:4e [ether] on eth0
? (192.168.207.210) at 00:50:56:b6:1e:91 [ether] on eth0
? (192.168.207.230) at 00:50:56:b6:e7:ed [ether] on eth0
? (192.168.207.3) at d0:50:99:9d:dd:b6 [ether] on eth0
? (192.168.207.224) at 1c:69:7a:92:0e:15 [ether] on eth0
node41 (192.168.207.41) at 00:50:56:b6:b9:a9 [ether] on eth0
node42 (192.168.207.42) at 00:50:56:b6:40:a8 [ether] on eth0
_gateway (192.168.207.250) at 00:50:56:a7:a8:94 [ether] on eth0# ip neigh
192.168.207.254 dev eth0 lladdr 00:25:90:94:0c:4e STALE
192.168.207.210 dev eth0 lladdr 00:50:56:b6:1e:91 STALE
192.168.207.230 dev eth0 lladdr 00:50:56:b6:e7:ed STALE
192.168.207.3 dev eth0 lladdr d0:50:99:9d:dd:b6 STALE
192.168.207.224 dev eth0 lladdr 1c:69:7a:92:0e:15 REACHABLE
192.168.207.41 dev eth0 lladdr 00:50:56:b6:b9:a9 REACHABLE
192.168.207.42 dev eth0 lladdr 00:50:56:b6:40:a8 REACHABLE
192.168.207.250 dev eth0 lladdr 00:50:56:a7:a8:94 REACHABLE
6.2 ARP 캐시 지우기
# ip neigh flush all
7. 방화벽 및 보안 설정
7.1 방화벽 규칙 확인
- iptables
# sudo iptables -L -v -n
Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
0 0 DOCKER-USER all -- * * 0.0.0.0/0 0.0.0.0/0
0 0 DOCKER-ISOLATION-STAGE-1 all -- * * 0.0.0.0/0 0.0.0.0/0
0 0 ACCEPT all -- * docker0 0.0.0.0/0 0.0.0.0/0 ctstate RELATED,ESTABLISHED
0 0 DOCKER all -- * docker0 0.0.0.0/0 0.0.0.0/0
0 0 ACCEPT all -- docker0 !docker0 0.0.0.0/0 0.0.0.0/0
0 0 ACCEPT all -- docker0 docker0 0.0.0.0/0 0.0.0.0/0
Chain OUTPUT (policy ACCEPT 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
Chain DOCKER (1 references)
pkts bytes target prot opt in out source destination
0 0 ACCEPT tcp -- !docker0 docker0 0.0.0.0/0 172.17.0.2 tcp dpt:5000
Chain DOCKER-ISOLATION-STAGE-1 (1 references)
pkts bytes target prot opt in out source destination
0 0 DOCKER-ISOLATION-STAGE-2 all -- docker0 !docker0 0.0.0.0/0 0.0.0.0/0
0 0 RETURN all -- * * 0.0.0.0/0 0.0.0.0/0
Chain DOCKER-ISOLATION-STAGE-2 (1 references)
pkts bytes target prot opt in out source destination
0 0 DROP all -- * docker0 0.0.0.0/0 0.0.0.0/0
0 0 RETURN all -- * * 0.0.0.0/0 0.0.0.0/0
Chain DOCKER-USER (1 references)
pkts bytes target prot opt in out source destination
0 0 RETURN all -- * * 0.0.0.0/0 0.0.0.0/0
- firewalld
# firewall-cmd --list-all
7.2 방화벽 임시 비활성화
- 방화벽 문제를 배제하기 위해
# systemctl stop firewalld
8. DNS 문제 해결
8.1 DNS 해석 확인
# nslookup estar987.com
Server: 8.8.8.8
Address: 8.8.8.8#53
Non-authoritative answer:
estar987.com canonical name = host.tistory.io.
host.tistory.io canonical name = blog-tistory-l51ybqnn.kgslb.com.
Name: blog-tistory-l51ybqnn.kgslb.com
Address: 27.0.236.139
# dig estar987.com
; <<>> DiG 9.11.36-RedHat-9.11.36-14.el8_10 <<>> estar987.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 33703
;; flags: qr rd ra; QUERY: 1, ANSWER: 3, AUTHORITY: 0, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 512
;; QUESTION SECTION:
;estar987.com. IN A
;; ANSWER SECTION:
estar987.com. 1800 IN CNAME host.tistory.io.
host.tistory.io. 300 IN CNAME blog-tistory-l51ybqnn.kgslb.com.
blog-tistory-l51ybqnn.kgslb.com. 10 IN A 27.0.236.139
;; Query time: 302 msec
;; SERVER: 8.8.8.8#53(8.8.8.8)
;; WHEN: Wed Jan 22 10:07:55 KST 2025
;; MSG SIZE rcvd: 128
8.2 DNS 서버 업데이트 또는 테스트
# vi /etc/resolv.conf
nameserver 8.8.8.8 //추가
9. 고급 도구 활용
9.1 tcpdump를 이용한 네트워크 분석
# tcpdump -i eth0
9.2 nmap으로 테스트
# nmap -sT 192.168.207.210
10. 로그 및 시스템 정보 확인
10.1 시스템 로그 확인
# journalctl -u network
-- Logs begin at Mon 2025-01-20 18:04:01 KST, end at Wed 2025-01-22 10:12:20 KST. --
-- No entries --
# cat /var/log/messages | grep -i network
Jan 20 21:12:51 Master10 NetworkManager[914]: <info> [1737375171.4551] audit: op="connection-update" uuid="d3c90e6e-06b4-3862-8dd2-f2a5244c83f0" name="Wired connection 1" args="connection.timestamp" pid=277982 uid=0 result="success"
# dmesg | grep -i eth
10.2 네트워크 드라이버 확인
# lspci -v | grep -i net
00:19.0 Ethernet controller: Intel Corporation Ethernet Connection I217-V (rev 05)
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