A packet with a ttl of 0 is called a *zero-length* packet. When a router receives a packet with a TTL of 0, it silently discards the packet. This behavior is not described in the RFCs that define the TTL field, and is not recommended. Discarding packets with low TTL values can cause problems for networks because it can lead to missed opportunities to send messages or data packets.
What technically happens…
- When a router receives a packet with a TTL of 0, the router discards the packet and sends an ICMP message to the sender.
- The ICMP message informs the sender that the packet was not delivered because the TTL expired.
- The sender can then take appropriate action, such as resetting the timer on the packet or increasing the TTL.
- Routers use TTL to prevent packets from being forwarded indefinitely and causing network congestion.
What is TTL?
The TTL is a value that is part of the IP header. It tells the router how many hops a packet has traveled before it reaches its destination
What does the ttl field represent?
The ttl field in an IP header represents the time to live (TTL) of a packet. The TTL is a number that is decremented by one each time the packet is forwarded. When the TTL reaches zero, the packet is destroyed.
When the packet is not completely ignored by the router…
The zero-length packet can be ignored. If the packet is not completely ignored, then the router adds it to the queue.
This is because the router will never forward the packet because it knows that the packet’s TTL value will never reach the destination. The packet will therefore be discarded.
The packet will be dropped if it is received at an IP address that is not on the network or if the destination is unreachable (because of a link failure, for example).
If the host is sending packets with a TTL == 0, then the host can send many packets without getting the error message “destination unreachable” or “packet too big”.
If the TTL is zero, the host may send data over the network but it will be dropped once it reaches the destination.
In the end
A router receiving a packet with TTL of 0 will discard the packet and send an ICMP message back to the sender. This is done to protect the network from unnecessary traffic and to prevent packets from traveling too far. It is important to remember this when creating your packets, as incorrect settings can cause problems for the network.
