What is the maximum value for the TTL field before a packet is dropped?

The maximum value for the Time to Live (TTL) field in an IP packet before it is dropped is indeed 0, but that indicates the packet should not be forwarded. Each time a packet passes through a router, its TTL value is decremented by 1. When the TTL reaches 0, the packet is considered to have "expired" and is dropped to prevent it from circulating indefinitely in the network. This is a vital mechanism to ensure that packets do not get stuck in routing loops, which can occur due to configuration errors or network changes.

While options like 128, 64, and 255 are plausible TTL maximums set by various operating systems or networking devices for newly generated packets, they do not reflect the specific threshold that leads to a packet being dropped. Starting values for many operating systems are commonly 64 or 128, but they are not the definitive value indicating when a packet will be discarded. The key takeaway is that once the TTL reaches 0 after being decremented multiple times as it traverses the network, the packet is dropped.