EC
ENETUNREACH
Linux / POSIXERRORNotableNetworkHIGH confidence

Network Is Unreachable

Production Risk

Check routing table and gateway configuration; common in misconfigured containers.

What this means

ENETUNREACH (errno 101) is returned when a connect() or send() fails because no route exists to the destination network. Unlike EHOSTUNREACH, this refers to the entire network being unreachable, not just a single host.

Why it happens
  1. 1No route to the destination network in the routing table
  2. 2Default gateway not configured
  3. 3Destination network behind a VPN that is disconnected
How to reproduce

connect() to an IP with no route in the routing table.

trigger — this will error
trigger — this will error
// Destination network 10.5.0.0/16 has no route
connect(sockfd, (struct sockaddr*)&addr, sizeof(addr));
// Returns -1, errno = ENETUNREACH

expected output

connect: Network is unreachable (ENETUNREACH)

Fix

Add a route or configure the default gateway

WHEN When ENETUNREACH is returned

Add a route or configure the default gateway
# Check routing table
ip route show

# Add a default gateway
ip route add default via 192.168.1.1

# Add a specific route
ip route add 10.5.0.0/16 via 10.0.0.1 dev eth0

Why this works

ENETUNREACH means no routing entry; add the missing route or default gateway.

Sources
Official documentation ↗

Linux Programmer Manual ip(7)

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