IPv4 TTL

What TTL Does

It represents the maximum number of hops (routers) a packet can traverse before being discarded.

Each router along the path decrements TTL by 1.

If TTL reaches 0, the router discards the packet and usually sends back an ICMP "Time Exceeded" message.

This prevents packets from looping endlessly in the network.

Typical Initial TTL Values

Different operating systems set different initial TTL values when sending a packet:

OS / Device Default TTL

Linux / Unix 64

Windows 128

Cisco / many routers 255

Some BSD/Unix variants 64 or 255

Different Network Paths (Asymmetric Routing)

Even if both hosts start with the same initial TTL, their packets might take different routes across the network.

If one path has more hops, the TTL when arriving at your capture point will be lower.