Error map
Reply from x: TTL expired in transit Networking: TTL expired in transit — routing loop between routers
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.
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).
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.
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 — Destination Host Unreachable / Destination net unreachable (ICMP type 3)
A router (or your own PC) tells you it has no way to deliver the packet to that address.
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: %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: 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.
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.
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: socket hang up / read ECONNRESET
The other side closed the TCP connection abruptly while your client was still using it.
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.
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.
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…
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.
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.
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…
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…
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: 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.
Cloudflare Error 1033: Argo Tunnel error (Cloudflare Tunnel not connected)
The hostname routes to a Cloudflare Tunnel, but no healthy cloudflared connector is running for it.
cloudflared: Unable to reach the origin service. The service may be down or it may not be responding to traffic from cloudflared (502)
The tunnel is connected, but cloudflared can’t reach your local service at the address in the ingress rule.
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: %CDP-4-NATIVE_VLAN_MISMATCH / device on the wrong VLAN can't reach the gateway
A port or trunk carries a different VLAN than expected, so hosts silently land on the wrong network.
Networking: %PM-4-ERR_DISABLE: psecure-violation error detected on Gi0/5, putting Gi0/5 in err-disable state
The switch shut the port down because a security or protection feature detected a violation.
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: nc -vz hangs then times out — firewall silently DROPs packets (REJECT would answer "Connection refused")
A connection attempt gets no answer at all, which points to a firewall dropping the packets rather than a closed port.
Networking: netstat -su: packet receive errors, receive buffer errors — UDP datagrams dropped by a full socket buffer
UDP packets arrive faster than the application reads them, so the kernel throws the extras away.
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.
ACM certificate stuck in Pending validation
ACM is waiting to see the DNS (or email) validation record — it wasn’t created, was created in the wrong DNS zone, or has a typo.
dial tcp: lookup registry-1.docker.io: no such host / Temporary failure in name resolution during docker build
DNS isn’t working for the Docker daemon or inside build containers, so pulls and package downloads fail.
DNS not working inside a Kubernetes pod (could not resolve host / nslookup: can't resolve)
Pods can’t resolve service names or external hosts — CoreDNS is down, blocked by NetworkPolicy, or the upstream resolver fails.
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