Troubleshooting, Locating And Solving Common Network Problems In Korean Kt Station Group

2026-03-31 20:29:00

Current Location： Blog > South Korea server

overview: network characteristics and common risks of kt station group

• kt has multiple backbone nodes in south korea, and the delay distribution is usually between 10-60ms;
• a site group usually consists of multiple vps/dedicated servers, and public ip pools and port restrictions require attention;
• common risks: bandwidth burst, tcp half-open connection, dns resolution anomaly, cdn back-to-origin problem;
• monitoring recommendations: use snmp/netflow and delay monitoring, and the traffic sampling period is recommended to be 1 minute;
• alarm threshold example: traffic exceeding 500mbps or pps>500k triggers an advanced alarm.

fault location process and tool list

• step 1: confirm the scope of impact (single machine/subnet/full site group), and group and investigate by ip segment;
• step 2: link detection, use mtr/traceroute to confirm the hop count and packet loss rate;
• step 3: host-side monitoring, check top/iostat/netstat/ss output;
• step 4: packet capture analysis, tcpdump -i eth0 -c 20000 host xyzw;
• step 5: upstream verification, check cdn back-to-origin, dns resolution and kt peer alarm records.

host/vps configuration and performance bottleneck examples

• recommended base configuration (example): 4 vcpu / 8gb ram / 100gb nvme / 1gbps port;
• performance traps: single-core saturation, high io wait, and large proportion of softirqs;
• network parameter tuning: net.core.somaxconn=1024, net.ipv4.tcp_max_syn_backlog=2048;
• nginx recommendation: worker_processes=auto, worker_connections=4096;
• resource monitoring: when 95% of the time cpu load>number of cores or iowait>30%, expansion or optimization is required.

host	cpu	memory	port bandwidth	typical traffic
vps-kr-01	4 vcpus	8gb	1gbps	average 120mbps, peak 600mbps
vps-kr-02	8 vcpus	16 gb	2gbps	average 300mbps, peak 1.2gbps

domain name/cdn/dns faqs and solutions

• dns resolution delays or errors: check ttls and upstream resolver connectivity;
• domain name resolution is inconsistent: compare the results returned by authoritative dns and recursive dns;
• cdn return to origin timeout: check the return to origin ip whitelist and firewall policy;
• cache penetration: set appropriate caching rules for dynamic interfaces or use tokens to prevent brushing;
• recommendation: set up secondary back-to-origin and load balancing. the peak cdn bandwidth needs to be estimated to be 130% redundant.

ddos defense strategy and recovery process

• identification characteristics: pps > 200k or traffic sudden increase > 300% in a short period of time are attack indicators;
• local protection: use conntrack/iptables speed limit and syn cookies enabled;
• cloud/upstream: contact kt or a third party for cleaning (example cleaning capacity: 10gbps/100mpps);
• drill recommendations: regularly drill back-to-source switching, black hole routing and traffic cleaning switching;
• recovery steps: first cut off abnormal traffic (acl/black hole), then gradually release it and observe the manslaughter rate.

examples of practical commands and log troubleshooting

• check the number of connections: ss -s and ss -tanp | grep syn | wc -l;
• packet capture example: tcpdump -nn -s0 -c 10000 -w dump.pcap host 1.2.3.4;
• iptables speed limit example: iptables -a input -p tcp --syn -m limit --limit 50/s --limit-burst 100 -j accept;
• log inspection: /var/log/nginx/access.log counts request peaks by time window;
• performance data reference: in a fault, it was observed that pps increased from 30k to 680k, resulting in softirq accounting for 80%.

real case: a certain kt station group was attacked by syn flood and the recovery process

• background: at 03:10 on 2025-03-12, the station group traffic suddenly increased from an average of 200mbps to 1.6gbps;
• impact: connection queue overflow occurred on multiple vpss, and nginx 502/504 errors surged;
• disposal: immediately enable iptables speed limiting and request kt on the cdn side to assist in starting cleaning (10gbps cleaning node);
• recovery: return-to-origin traffic drops to normal within 15 minutes, manslaughter <0.5%, and business gradually recovers;
• lesson: it is recommended to retain at least 1:3 cleaning bandwidth budget and automated switching strategy all year round.

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