The default gateway is the first hop for traffic leaving the local subnet, so reachability problems there can make most external services appear down even when the host has a valid IP configuration.

Linux selects the gateway using routing and policy rules, then resolves the gateway IP to a MAC address using ARP (or NDP for IPv6). A short ping test confirms Layer 3 reachability and latency, while the neighbor cache in ip neigh confirms whether link-layer resolution to the gateway is working.

Some gateways rate-limit or filter ICMP echo requests, and VPN clients can change the effective first hop, so results are most reliable when a route lookup, ping, and neighbor state are checked together. Keep probes short on constrained links and treat persistent FAILED neighbor state as a stronger signal than a single missed ping reply.

Related: How to troubleshoot a Linux network outage
Related: How to check network interface link state in Linux

Steps to check gateway reachability with ip and ping in Linux:

  1. Identify the gateway address from the default route. 
    $ ip route show default
default via 192.0.2.1 dev eth0 proto dhcp src 192.0.2.40 metric 100

    Related: How to check the default route in Linux

  2. Confirm the gateway is selected for an off-subnet destination. 
    $ ip route get 203.0.113.50
203.0.113.50 via 192.0.2.1 dev eth0 src 192.0.2.40 uid 0 
    cache

    The via address is the first hop and dev is the interface used to reach it.

  3. Ping the gateway to measure reachability and packet loss. 
    $ ping -c 4 192.0.2.1
PING 192.0.2.1 (192.0.2.1) 56(84) bytes of data.
64 bytes from 192.0.2.1: icmp_seq=1 ttl=128 time=0.218 ms
64 bytes from 192.0.2.1: icmp_seq=2 ttl=128 time=0.280 ms
64 bytes from 192.0.2.1: icmp_seq=3 ttl=128 time=0.636 ms
64 bytes from 192.0.2.1: icmp_seq=4 ttl=128 time=1.31 ms

--- 192.0.2.1 ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3090ms
rtt min/avg/max/mdev = 0.218/0.610/1.307/0.432 ms

    Use -c to keep the test bounded and add -n to skip name resolution during troubleshooting.

  4. Check the neighbor table for a resolved MAC entry and state. 
    $ ip neigh show 192.0.2.1
192.0.2.1 dev eth0 lladdr 02:00:00:00:00:01 REACHABLE

    REACHABLE, STALE, or DELAY indicates successful Layer 2 resolution, while INCOMPLETE or FAILED indicates unresolved gateway MAC and a likely link, VLAN, or switch-port issue.

  5. Inspect interface counters for errors or drops on the gateway interface. 
    $ ip -s link show dev eth0
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP mode DEFAULT group default qlen 1000
    link/ether 02:00:00:00:00:10 brd ff:ff:ff:ff:ff:ff
    RX:  bytes packets errors dropped  missed   mcast           
      40419857  115529      0       0       0       0 
    TX:  bytes packets errors dropped carrier collsns           
        641101    9829      0       0       0       0

    Rising errors, dropped, or carrier counts often point to cabling, Wi-Fi quality, or switch-port problems affecting gateway reachability.