Cisco "ping" Command Explained
ping — tests reachability by sending ICMP echo requests and reporting replies and round-trip times — the universal first connectivity test. Runs in user or privileged EXEC mode.
Syntax and common variants
| Variant | Purpose |
|---|---|
ping 8.8.8.8 | Basic reachability test (5 packets) |
ping 10.1.1.1 source loopback0 | Test from a specific source interface |
ping 10.1.1.1 repeat 100 size 1500 | Volume/size testing (MTU checks) |
ping (extended, no args) | Interactive mode: count, size, DF-bit, source |
Reading the output
| Output / element | Meaning |
|---|---|
!!!!! | Replies received — success |
..... | Timeouts — no reply (filtering, no route, host down) |
U | Destination unreachable — a router said “no route” |
Success rate is 80%… | Summary + min/avg/max round-trip times |
When to use it
Start every connectivity troubleshoot here, then move outward: ping the gateway, then a remote hop, then the destination — the first failure marks the broken segment. Extended ping with source/DF/size options finds asymmetric routing and MTU issues. Browse more in the command reference or practise in the free labs.
Frequently asked questions
What do the dots mean in ping output?
Each dot is a timeout — the packet went unanswered. Mixed !.!.! patterns often mean congestion or an ARP delay on the first packet.
Why ping with a source interface?
To test the return path as another network would see it — verifying remote routers know the route back to that source.
Ping works but the application doesn't — why?
ICMP proves basic reachability only; the app's specific port may be blocked by a firewall or the service may be down.
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