Use The Monitoring Tool To Locate The Problem Of The Us Cn2 Server Being Unable To Reach Certain Areas. Steps

faced with the problem of unreachable access to us cn2 servers in some areas, it is crucial to choose appropriate monitoring tools . the cheapest solution is usually to use the system's built-in commands (such as ping, traceroute, mtr) and free online route viewing on the public network (such as bgplay, looking glass) for preliminary troubleshooting; the most practical combination is to use distributed probes (such as ripe atlas, cloudping) + visualization tools (such as pingplotter, smokeping) for continuous monitoring; the best (enterprise-level) solution is to use a commercial-grade saas monitoring platform (such as thousandeyes, catchpoint) combined with bgp visualization and traffic packet capture, which can quickly locate cross-asn or cross-pop link problems and generate evidence that can be used for operation and maintenance and isp communication.

first, clarify the meaning of "calls cannot be made to some areas" and collect affected provinces/cities, isps, node examples, and time windows. record the ip, domain name, connection method (direct connection or load balancing) of the target server, and whether there are multiple exits or cdn. prepare at least one probe located in the united states or abroad, as well as multiple domestic test points from different operators and different provinces, for horizontal comparison. use this information as baseline data for subsequent analyses.

execute ping and traceroute (tracert on windows, traceroute or mtr on linux) locally or in the affected area respectively. record round trip delay (rtt), packet loss rate and hop count. if ping times out but traceroute disappears after a certain hop, the problem may lie in subsequent links or icmp rate limiting. pay attention to comparing the results of different regions and operators. if only some operators or provinces have abnormalities, the problem is most likely the interconnection between operators or the routing strategy to the cn2 dedicated line.

mtr (or pingplotter under windows) can simultaneously report the packet loss and delay changes of each hop, which is suitable for determining which link begins to experience packet loss or delay increase. it is recommended to run for a period of time during peak and off-peak periods (for example, once per second for 5-10 minutes) and save the output. if packet loss is concentrated on a certain router or asn transfer point, the problem is with the link side or peer policy.

use looking glass provided by the isp or public bgp services (such as bgp.he.net, routeviews) to view the bgp path to the target ip and compare the differences in as paths at different observation points. if it is found that some areas choose to bypass (longer as-path) or are directed to different egress ass, it means that there are differences in routing policies or bgp injection. record the as number, next hop and time point of the problem to facilitate communication with the operator.

to accurately determine the boundaries of "some areas", it is recommended to use distributed probes such as ripe atlas or deploy lightweight probes on global nodes (cloud hosts) for batch traceroute and http/tcp detection. comparing the probe results of different provinces in mainland china, hong kong, taiwan, japan and south korea, and the east/west united states, if there are consistent problems in certain provinces or isps in the mainland, but the overseas probes are normal, the problem most likely occurs in the international export or domestic to export bearer links.

perform tcpdump packet capture on the controllable node, especially in scenarios where the three-way handshake is not completed or rst is in progress. check whether there are problems caused by tcp windows, mss/mtu, or fragmentation. use ping -m do -s (linux) to test the mtu to see if the connection establishment exception is caused by the intermediate device discarding fragments or pmtud failure. if a large number of tcp retransmissions or syn blocks are found, filtering policies or firewall rules should be considered.

confirm that the affected service ports (such as 80/443/22, etc.) are not rate-limited or blocked on the target host and intermediate firewalls. use telnet or nc to test whether the tcp three-way handshake can be established at each test point. some isps will impose policy restrictions on specific ports or protocols, especially on cross-border links. you need to verify whether the instability is caused by qos or traffic cleaning policies.

cn2 links usually have specific as numbers and exit node characteristics, and "telecom" or cn2 related hop labels can be observed through traceroute. if access congestion or packet loss occurs only after passing through the cn2 node, you need to communicate with the operator responsible for the bearer of this segment, provide traceroute, mtr and tcpdump evidence, and ask them to check the link quality, mpls label and queuing policy.

the compiled evidence list includes: affected isp/region, time period, traceroute/mtr output (marked with abnormal hop count), tcpdump fragments and bgp path difference map. when submitting a work order, provide comparative data (normal points and abnormal points), and attach possible conclusions (for example, "packet loss is concentrated at the transfer point between asn x and asn y"). clear evidence makes it easier for operators to locate and repair.

short-term options include: adjusting the load balancing priority, adding backup exits, using cdn or overseas elastic public ip for switching, and enabling vpn or dedicated line acceleration services; in the long term, you should negotiate with the upstream isp to optimize the bgp strategy, apply for a more stable overseas link, or upgrade to a higher-level dedicated line service (such as cn2 gt/ct). at the same time, continuous monitoring and alerting is deployed to detect regressions or new problems in a timely manner.

locating the problem that the us cn2 server is inaccessible in some areas requires gradual progress from basic connectivity testing, distributed probes, bgp path analysis to packet capture and in-depth investigation. the cheapest way is to combine ping/traceroute/mtr with free looking glass to quickly locate; the best practice is to use distributed probes and commercial monitoring platforms to generate evidence-based reports and cooperate with operators to fix them. it is recommended to use free tools to confirm the location and range before deciding whether to invest in commercial monitoring or dedicated line optimization to ensure long-term stability.