Error map
Reply from 192.168.1.1: Destination host unreachable Networking: ping — Destination Host Unreachable / Destination net unreachable (ICMP type 3)
Networking · layer 2, Network
Centre: this error. First ring: errors it is linked with (12). Outer ring: what those are linked with. Colours show the layer of a request each error belongs to. Click any dot to re-centre the map on it; hover to follow its connections. The centre dot opens the error page.
Directly related (12)
HTTP 404 Not Found
The server can’t find anything at the requested URL.
connect: No route to host (EHOSTUNREACH)
The destination host isn’t reachable — it’s down, on another subnet without routing, or a firewall rejects with “host unreachable…
Cloudflare Error 1019: Compute server error (Workers)
A Cloudflare Worker routed the request to a loop or hit an internal compute error.
connect: Network is unreachable (ENETUNREACH)
The host has no route to the destination network — no default gateway, interface down, or trying IPv6 without IPv6 connectivity.
HTTP 405 Method Not Allowed
The URL exists, but it doesn’t accept the HTTP method you used (e.g. POST to a GET-only route).
SMTP: 554 5.4.14 Hop count exceeded - possible mail loop
The message passed through too many mail servers (usually over 25), which almost always means two systems forward mail to each ot…
Networking: ping — Request timed out / 100% packet loss (host drops or filters ICMP)
No echo reply arrived in time: the host is down, unreachable, or simply ignores ping.
Networking: PING: transmit failed. General failure. / ping: sendmsg: Operation not permitted
The operating system could not even send the packet, so the problem is local (adapter, route or firewall), not the remote host.
Networking: Two hosts on one LAN can't talk — subnet mask or network address mismatch
The hosts disagree about which addresses are local, so one tries to route traffic that should go straight across the LAN.
Networking: VPN is connected but I can't reach the internal network — missing routes, split tunnel or overlapping subnets
The tunnel is up, but traffic for the office/VPC subnets isn't sent through it or comes back the wrong way.
Networking: `arp -n` shows (incomplete) / Destination Host Unreachable — no ARP reply from the next hop
The machine asked "who has this IP?" and nobody on the local network answered.
Networking: TTL expired in transit — routing loop between routers
A packet ran out of hops before arriving, which usually means two routers keep sending it back and forth.
Two steps away (36)
HTTP 403 Forbidden
The server understood the request but refuses to authorize it — you (or the server process) are not allowed to access this resour…
HTTP 410 Gone
The resource used to exist but was intentionally and permanently removed, with no forwarding address.
SyntaxError: Unexpected token < in JSON at position 0
`JSON.parse()` / `response.json()` received something that isn’t JSON — very often an HTML error page.
Error: connect ECONNREFUSED 127.0.0.1:5432
Nothing is listening at that host:port — the target service is down or you’re connecting to the wrong address.
Error: socket hang up / read ECONNRESET
The other side closed the TCP connection abruptly while your client was still using it.
Cloudflare Error 1020: Access Denied
A Cloudflare firewall/WAF custom rule blocked the request — the visitor’s IP, country, user agent or request pattern matched a bl…
Whitelabel Error Page — This application has no explicit mapping for /error
Spring Boot’s default error page — the request hit no controller mapping (404) or a controller threw (500).
TypeError: Missing parameter name at 1 (path-to-regexp)
An Express 5 (path-to-regexp v8) route uses old wildcard syntax like '*' or '/:id?'.
No routes matched location "/x"
React Router found no route definition for the current URL.
Error: getaddrinfo ENOTFOUND host / Name or service not known
DNS lookup for the hostname failed — the name is wrong, doesn’t exist, or this machine can’t resolve it.
Error: NextRouter was not mounted.
next/router’s useRouter was used inside the App Router (app/ directory), which uses next/navigation instead.
API Error: Cannot GET /api/... / No route matches / The route could not be found
The server has no route for this URL and HTTP method combination — the endpoint path, API version prefix or method is wrong.
HTTP 400 Bad Request
The server could not understand the request because its syntax, headers or body are malformed or invalid.
CORS Error: No 'Access-Control-Allow-Origin' header is present
The browser blocked a cross-origin request because the server’s response didn’t include the CORS headers allowing your site’s ori…
HTTP 501 Not Implemented
The server doesn’t support the functionality (usually the HTTP method) needed to fulfil the request.
WordPress REST API: {"code":"rest_no_route","message":"No route was found matching the URL and request method."}
The REST endpoint doesn’t exist for that URL and HTTP method — wrong namespace/route, plugin not active, or route registered too…
Laravel: The GET method is not supported for route x. Supported methods: POST (MethodNotAllowedHttpException)
The URL exists, but not for the HTTP method used — e.g. opening a POST-only route in the browser, or a form sending GET.
SMTP: 421 4.7.0 Our system has detected an unusual rate of unsolicited mail originating from your IP address. Mail sent from your IP address has been temporarily rate limited
The receiving server (often Gmail or Outlook) is temporarily throttling your mail because the volume or reputation of your sendin…
driver failed programming external connectivity on endpoint: iptables: No chain/target/match by that name
Docker’s iptables rules were wiped (firewalld/ufw reload, iptables flush) while Docker was running, so it can’t publish ports.
ssh: connect to host x port 22: Connection timed out
SSH packets get no reply — a firewall/security group drops them, the server is off, or the IP is wrong.
Azure SQL: Cannot open server 'x' requested by the login. Client with IP address 'y' is not allowed to access the server (Error 40615)
The Azure SQL server firewall doesn’t allow your client’s IP address.
Docker Desktop: WSL 2 installation is incomplete / WSL update required
Docker Desktop on Windows needs WSL 2 and its Linux kernel; they’re missing, outdated or disabled.
Networking: Network cable unplugged / `ip link` shows NO-CARRIER state DOWN / Ethernet: Network cable unplugged
The network card sees no electrical link, so nothing above it (IP, DNS, browser) can work.
Networking: No Wi-Fi networks found — the Wi-Fi adapter is missing, disabled or its driver failed
The operating system doesn't see a working wireless adapter, so no networks can be listed.
Networking: Windows has detected an IP address conflict / Duplicate address detected by 00:aa:bb:cc:dd:ee
Two devices on the same network are using the same IP address, so traffic reaches the wrong one or neither.
Networking: Windows: Default gateway is not available / Diagnose Connection Problems: DHCP not enabled
The PC can't reach its router, so it has no path out of the local network.
Networking: IPv4 address 169.254.x.x (Autoconfiguration / APIPA) — the PC couldn't get an address from DHCP
With no DHCP answer, the computer gave itself a link-local 169.254.x.x address, which only works on the local segment.
Networking: SSH/HTTPS connects but hangs on large data — path MTU discovery black hole
Small packets pass but full-size ones vanish, so logins work and then transfers or page loads stall.
Networking: %OSPF-5-ADJCHG: Nbr 10.0.0.2 from EXSTART to DOWN — OSPF neighbor stuck in EXSTART/EXCHANGE (MTU mismatch)
Two OSPF routers see each other but never finish exchanging databases, cycling between EXSTART and DOWN.
Networking: Handshake for peer did not complete after 5 seconds, retrying (try 2) — WireGuard tunnel never establishes
The WireGuard peers can't complete the cryptographic handshake, so no traffic flows.
Networking: Wi-Fi keeps disconnecting / signal -80 dBm / wlan0: deauthenticating by local choice (reason=3)
The wireless link is too weak or too noisy to hold, so the client drops and rejoins repeatedly.
Networking: Interface down — SFP transceiver Loss of Signal / no receive light
A fibre or SFP link is down because the transceiver receives no light.
Networking: wlan0: WPA: 4-way handshake failed - pre-shared key may be incorrect / WRONG_KEY
The Wi-Fi association started but key negotiation failed, almost always a wrong password.
Networking: ping: local error: message too long, mtu=1500 / Packet needs to be fragmented but DF set
A packet is larger than the path MTU and is marked "don't fragment", so a router discards it.
Networking: ICMP Destination unreachable (Port unreachable) — UDP packet sent to a port where nothing is listening
A host answered a UDP packet with an ICMP message saying no program is listening on that port.
Networking: DNS changed but the domain still resolves to the old IP — TTL and resolver caching ("propagation")
You updated a DNS record, but resolvers and devices keep serving the old answer until its TTL expires.
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