Hop count is the number of intermediate devices, normally routers, that a packet crosses on its way from source to destination. Each time a router forwards the packet, that is one hop.
Why it matters
More hops generally mean more places for delay and failure, but hops are not equal: one hop may be a short office link while another crosses an ocean, so hop count is a rough indicator rather than a measure of speed. Some routing protocols, such as RIP, use hop count as their metric and treat 16 as unreachable. In IP, a packet's TTL field is decremented at every hop and the packet is discarded at zero, which stops routing loops and is the mechanism traceroute uses to reveal each hop.
Example
$ traceroute -n example.com
1 192.168.1.1 1.2 ms
2 10.20.0.1 8.9 ms
3 203.0.113.1 14.0 ms
4 198.51.100.9 22.7 msThis path has four hops. If hop 3 shows * * *, that router is probably not answering probes; it may still forward traffic normally.
Common mistakes
- Treating a higher hop count as proof of a slower route.
- Reading a single slow intermediate hop as the cause of a problem when later hops are fine.
- Confusing hop count with the TTL value in a DNS record; they are different things.
Related
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