You are unable to reach hosts on the Internet. Briefly explain how you would test if the problem is within your network or outside your network (ie your service provider or further upstream).
Try an answer before revealing the guidance below.
Key Concepts
- Ping
- Default gateway
- Traceroute
- Hop-by-hop isolation
Answer Approach
- Start at your own host and default gateway.
- Move outward to your edge router and the ISP’s first hop.
- Use traceroute to see the last hop that responds.
- Decide which side of your network boundary that hop is on.
Full Answer
Answer status: Draft answer (unofficial). Revision notes, not an official marking scheme.
Test outward step by step. Ping your default gateway and other internal hosts: if they fail, the problem is inside your network. Then ping your border router’s external interface and the ISP’s first-hop router or DNS server. Traceroute to an external host shows the last router that replies: if replies stop inside your network, the fault is local; if they reach the ISP and stop there or further upstream, the problem is outside your network. (ICMP filtering can hide some hops, so interpret silent hops with care.)
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