Identifying Network Routing Anomalies Using ASN Lookups

CS0-003 By islever Editorial Last updated

Given a scenario, analyze indicators of potentially malicious activity Given a scenario, use appropriate tools or techniques to determine malicious activity

Short answer

C The analyst should use the dig function to query the ASN via Cymru’s service, as this identifies the originating Autonomous System and detects routing anomalies like hijacks that traceroute cannot reliably verify.

Question

A security analyst is trying to identify anomalies on the network routing. Which of the following functions can the analyst use on a shell script to achieve the objective most accurately?
  1. function x() { info=$(geoiplookup $1) && echo "$1 | $info" }
  2. function x() { info=$(ping -c 1 $1 | awk -F "/" ’END{print $5}’) && echo "$1 | $info" }
  3. function x() { info=$(dig $(dig -x $1 | grep PTR | tail -n 1 | awk -F ".in-addr" ’{print $1} ').origin.asn.cymru.com TXT +short) && echo "$1 | $info" } Correct Answer
  4. function x() { info=$(traceroute -m 40 $1 | awk ‘END{print $1}’) && echo "$1 | $info" }

Key Takeaways

The main trap is confusing simple path visualization (traceroute) with security validation of route origins (ASN lookup). Anomalies are defined by unauthorized AS participation, not just path length.

This question tests the ability to detect network routing anomalies using shell scripting tools. The correct approach involves querying Autonomous System Numbers (ASN) to validate route origins.

Common mistake: Option D (traceroute) is commonly chosen because it visually displays the network path. However, it fails to identify if the route itself is malicious or hijacked, as it doesn't verify the Autonomous System ownership.

Expert Analysis

The question asks for the most accurate method to identify anomalies on the network routing using a shell script. In security operations, 'network routing anomalies' typically refer to BGP hijacks, route leaks, or unexpected path changes where traffic is directed through an untrusted or incorrect Autonomous System (AS).

Option C uses dig to perform a reverse DNS lookup and then queries origin.asn.cymru.com TXT, which returns the Autonomous System Number (ASN) associated with the IP address. By knowing the expected ASN for an IP, a security analyst can detect if traffic is being routed through a different AS than usual, which is a definitive indicator of routing manipulation or hijacking.

Option D (the most attractive wrong answer) uses traceroute. While traceroute shows the hop-by-hop path, it only reveals the immediate next hops and final destination. It does not provide context about the ownership or policy of the networks involved. A single hop in a traceroute might look normal even if the broader path is compromised by a BGP leak elsewhere. Therefore, traceroute identifies path but not necessarily routing anomalies in the security sense of AS integrity. Comments favoring D often confuse 'seeing the route' with 'detecting routing attacks'. The key distinction is that ASN verification (C) validates the legitimacy of the route origin, whereas traceroute (D) just maps connectivity.

Official Reference

These links open the official vendor documentation in a new tab.

Exam Strategy

When a question mentions 'routing anomalies,' 'hijacks,' or 'unexpected paths,' prioritize solutions that involve ASN verification or BGP monitoring. Tools like traceroute are useful for basic connectivity troubleshooting but lack the contextual data needed to confirm if a route is legitimate or malicious. Always look for options that link IP addresses to their owning organizations or AS numbers.

Frequently Asked Questions

Why is traceroute not sufficient for detecting routing anomalies?

Traceroute shows the physical or logical path packets take, but it does not verify the ownership of the networks at each hop. A hijacked route might still show a valid path structure, making ASN verification essential to detect malicious rerouting.

What does the Cymru ASN service provide?

The Cymru ASN service allows users to query IP addresses via DNS to retrieve the associated Autonomous System Number (ASN) and owner information, helping verify if traffic is coming from the expected network.

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Discussion 24 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 24

  1. chaddman 👍 17
    D. function x() { info=$(traceroute -m 40 $1 | awk 'END{print $1}') && echo "$1 | $info" } This shell function uses traceroute to trace the route packets take to reach the destination specified by $1. The -m 40 option specifies a maximum of 40 hops for the trace. The awk 'END{print $1}' part extracts the final hop from the traceroute output, and then the function echoes the destination and the info.
  2. nmap_king_22 👍 7 Answered D
    To identify anomalies on the network routing accurately, the security analyst should use a function that can help in gathering information related to the network routing of a given IP address. Among the provided options, the most suitable function for this purpose is: D. function x() { info=$(traceroute -m 40 $1 | awk 'END{print $1}') && echo "$1 | $info" } Explanation: This function uses the "traceroute" command with a maximum hop count of 40 to trace the route to the target IP address. The "awk 'END{print $1}'" command is used to extract the last hop or router in the route, which can be valuable for identifying anomalies or unexpected routing paths. Finally, it echoes the target IP address and the last hop/router in the route as output, which can help the analyst identify any unexpected or suspicious routing behavior.
  3. CyberMom 👍 5 Answered C
    Reverse DNS Lookup (dig -x $1) Resolves the IP address into a domain name. Extracts the PTR Record (grep PTR | tail -n 1 | awk -F ".in-addr" '{print $1}') Pulls out the host information from the PTR record. Queries Cymru WHOIS ASN Database (origin.asn.cymru.com TXT +short) Retrieves ASN information, which identifies the network owner and routing information. This helps detect suspicious or hijacked routes.
  4. cy_analyst 👍 4 Answered C
    This function retrieves the ASN information for an IP address. The process starts by performing a reverse DNS lookup to get the domain name associated with the IP address, then queries the Cymru ASN service to get detailed ASN and routing information about the IP address. This can be useful for identifying which network or organization controls a particular IP address and can help with detecting anomalies in routing if, for example, traffic is being routed through an unexpected ASN.
  5. Nishaw 👍 4 Answered C
    This function performs a reverse DNS lookup (dig -x $1) on the IP address $1 to get the corresponding domain name. It then extracts the Autonomous System Number (ASN) information from the result using awk and queries the ASN information from the origin.asn.cymru.com service. This can help identify anomalies in network routing by associating IP addresses with their corresponding ASN, providing insights into the routing path and potential routing issues.
Show 19 more comments
  1. Susan4041 👍 4 Answered C
    D only gives hops and shows packet loss I am not sure how you can find anomalies from that. I vote C as it shows ,when you're analyzing routing anomalies — they reveal how IPs are announced on the internet and can uncover hijacks, misrouting, or malicious routes.
  2. shadmane 👍 3 Answered C
    The goal is to identify anomalies in network routing. Analyzing routing anomalies often involves identifying the Autonomous System (AS) associated with IP addresses. The function in C performs a reverse DNS lookup to find the PTR record of the IP address, uses the result to query the ASN information, and retrieves the AS details using the Cymru WHOIS service. This approach provides the most accurate and relevant routing information for identifying network anomalies compared to options like geoiplookup (A) or ping (B), which provide limited or unrelated routing insights. Traceroute (D) shows pathing but does not directly provide AS or routing anomaly detection information.
  3. Geronemo 👍 3 Answered D
    This function executes a traceroute to the specified IP address and extracts the last hop reached. Traceroute can reveal the network path taken by packets, helping to identify routing anomalies such as unexpected hops or routing loops. Among the options provided, option D (traceroute) is the most relevant for identifying anomalies on the network routing.
  4. LiveLaughToasterBath 👍 3 Answered D
    network anomalies. I'd start with a traceroute to see the nodes my connection runs through. I do this when customer's are having non-equipment related problems, related to internet connection. All ISPs are interconnected and if they lose a node, traffic may be re-routed, which can increase latency.
  5. maigoya 👍 3 Answered D
    Among the provided options, option D (traceroute) is the most suitable for identifying anomalies on the network routing. Traceroute provides detailed information about each hop packets take to reach the destination, allowing the analyst to detect any unusual routing paths or issues.
  6. friendlyneighborhoodITguy 👍 3 Answered C
    Groq - The best option for identifying anomalies on network routing is C. This function uses Cymru IP to ASN mapping, providing accurate origin ASN information for the given IP address.
  7. vannydabest 👍 3 Answered C
    Chat GPT says C due to getting ASN info from DNS
  8. Freshly 👍 2
    Correct answer hear is D. Don't forget we can't always answer this the way we would handle this in real life but more specifically the question wants the result for network routing. That is a trace route command basics all day. Trace route will tell us 4 key things here: hop by hop path (can't get this with C), router info (ip addresses so we know who or what has been in communication with our data), response times, and packet loss. If I want to know where my packets are going in the network and the path they take, bottlenecks, or path shortening for quicker communication (referring to network+), this is what you need to use. Most importantly this command allows us to see path changing that our data takes by being able to see all of the hops the data takes. What if its intercepted and sent to a C2C before arriving at its destination? Can't do that with C.
  9. Thunder_Cat 👍 2 Answered D
    Explanation: traceroute -m 40 $1: Runs a traceroute with a maximum of 40 hops to analyze the route a packet takes to a given destination. awk 'END{print $1}': Extracts the last hop IP, which helps identify unexpected routes or reroutes (potential anomalies). echo "$1 | $info": Prints the input destination and the final hop, allowing for easy anomaly detection. This function is effective because it helps detect if a destination is taking an unusual or unexpected route, which could indicate routing anomalies, BGP hijacking, or malicious reroutes.
  10. Freshly 👍 2
    C will give us more info about where our data ended up at and only gives us the LAST HOP that data took. That is NOT what comptia wants. Don't believe me, look at question #64. There is where you will choose C. I wish you all good luck. Don't overthink this one.
  11. G0x47 👍 2 Answered D
    To find the Routing anomalies we should use tool like traceroute.
  12. ms123451 👍 2 Answered D
    Option C captures ASN info, D monitors the routes.
  13. robizman 👍 1 Answered C
    Answer: C Option C Is best because: Option C performs an ASN lookup via Team Cymru’s DNS service, which maps IP addresses to their originating autonomous system numbers. By extracting the PTR record, then querying origin.asn.cymru.com for the ASN, you can: Identify which network (autonomous system) the IP belongs to Detect unexpected AS changes or hijacks when the ASN doesn’t match the expected owner Aggregate traffic or alerts based on ASN boundaries, highlighting routing anomalies This method provides a precise view of routing ownership—far more informative for anomaly detection than simple latency, geolocation, or traceroute hop counts.
  14. Gway 👍 1
    D: Uses traceroute to display the route packets take to reach a network host. For identifying anomalies in network routing, the function that would be most relevant is: D. function x() { info=$(traceroute -m 40 $1 | awk ‘END{print $1}’) && echo "$1 | $info" } traceroute shows the path that packets take to get from the source machine to the destination. This can help identify if there are unexpected or inefficient routes, timeouts, or other anomalies that might indicate a routing issue. The other functions gather useful data but are not as directly applicable to identifying routing anomalies.
  15. lNSOMNiA 👍 1 Answered C
    The function in option C is the most suitable for identifying routing anomalies because it leverages DNS and AS information, providing a comprehensive look at the network routing infrastructure relative to the IP address in question. It enables the analyst to see if the traffic to and from the IP address is being routed through expected or unexpected AS paths, which is crucial for detecting anomalies in network routing.
  16. kazeus 👍 1 Answered C
    I Originally thought it was D but the end of that script takes only the last line and prints only the first field. Thats not nearly enough routing information to be correct. The answer is C. ASN is associated with Internet Routing (BGP) so it can identify IP's unexpectedly belonging to a different system or traffic being associated with an unexpected network/provider.
  17. 1574aa7 👍 1 Answered D
    I pick D because it says that it wants to find anomalys in the routing , and i went to check with chat gpt and confirmed it as well Conclusion (per CompTIA logic): To identify anomalies in routing, you want to see the actual route, and that's exactly what traceroute does. Correct answer: D — This aligns with both real-world analysis and CompTIA exam logic.
  18. cy_analyst 👍 1
    function x() { info=$(traceroute -m 40 $1 | awk ‘END{print $1}’) && echo "$1 | $info" }: This uses traceroute, which helps map the path traffic takes, but it only gives you the final hop, which may not provide enough detail for anomaly detection in routing.
  19. tailogdavid1987 👍 1 Answered D
    traceroute maps the actual path packets take to a destination, revealing anomalies.

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