What Happens When A Router Receives A Packet With A TTL Of 0?

What Happens When A Router Receives A Packet With A TTL Of 0 is a common question among network students. When a router gets a packet with zero TTL, it usually dabs it, and it then uses an ICMP TTL to send a packet back to the Host IP. The packet gets discarded if the TTL hits zero.

The hosts will continue to transmit and receive traffic. Even yet, it’s probable that traffic will not always arrive at its destination. So, if you’re wondering the same thing and want a comprehensive answer, you’ve come to the right spot.

Quick Answer: The packet gets discarded if the TTL hits zero. The router that lost the IP packet with a TTL of 0 sends an Internet Control Message Protocol message type 11 with the code 0 to the IP packet’s originator.

Continue reading the article to learn what happens to a packet when the TTL field gets set to 0.

What Is A Router?

A router is a piece of hardware that links together many packet-switched networks. It has two primary purposes: controlling traffic between networks and allowing several devices to connect to the Internet simultaneously.  

They get used for various things, including Internet access, network coupling, and VPN connections between a branch and central offices. The network layer address gets used to switching data packets through the router in the OSI layer model.

Although there are a few options, most routers transfer data across LANs and WANs. A local area network is a collection of linked devices that is limited to a particular geographic region; a vast area network is an extensive network that spans a large geographic area

In addition to routers that utilize the Internet protocol (IP), multi-protocol routers may handle a range of additional network protocols.

How does A Router work?

Before giving a direct answer to What Happens When A Router Receives A Packet With A TTL Of 0? Let us understand how a router works.

Assume a router as an air traffic controller, with data packets representing planes traveling to different airports. Routers use packets to guide and steer network data, including files, chats, and simple transfers such as web activities.

Each packet must be steered to its destination as effectively as possible, just as each plane has a different destination and takes a unique path. The router reads the header of a packet to identify its destination.

what is a router

Identifying information such as size, sender, data type, and, most significantly, the destination IP address gets included in one of the layers, or sections, of the data packets.

The router uses the routing table to find the most efficient path to that destination. The packet gets subsequently sent to the following network along the route. The router reads this layer and prioritizes the data, choosing the optimal path for each transmission.

What Is ICMP?

The Internet Control Message Mechanism (ICMP) is a protocol for communicating data transport concerns between network devices. ICMP functions similarly to how a carpenter and a home improvement business communicate in network communication.

It delivers notifications to the sender about data that was supposed to come from the receiver. But If the data does not reach the intended recipient or gets received in an improper order. In that case, ICMP informs the sender, allowing the message to be resent. A device uses ICMP to communicate transmission difficulties with a data packet’s sender.

If a datagram gets not delivered, ICMP may send a message to the host, including information that may assist the host in determining what went wrong with the transmission. A distributed denial of service assault, such as an ICMP flood, a ping of death, or a Smurf attack, can bring a network to a halt (DDoS).


How To Block Emails On iCloud? Read Our Comprehensive Guide Here.

TTL – What  0 or 1?

The time to live refers to the length of time a packet gets allotted to stay in a network before being rejected by a router (TTL). The sender sets the TTL field of the datagram, which each router decreases along the way to its destination.

TTL values represent the packets’ maximum range, which commands ping and traceroute get commonly used in networks.

The sender host specifies the initial TTL value as an eight binary digit field in the packet header. When a packet of data is formed and sent across the Internet, there’s a chance it’ll bounce back and forth between routers endlessly.

To prevent this, packets are constructed with a time-to-live or hop limit that expires after a certain amount of time.

What Happens When A Router Receives A Packet With A TTL Of 0?

Now we have all the required knowledge to answer your query of What Happens When A Router Receives A Packet With A TTL Of 0?

The router will use its measure to shorten the TTL, and if the value is 0 or below, the packet will drop. Suppose your packet did not reach its intended destination before the TTL expired.

In that case, your machine will get an ICMP message type 11 and code 0 message stating that the destination host is unreachable. When the source user receives this message, it must first determine a problem, such as a routing difficulty when transmitting to this specific site or a low beginning TTL value.

So, if the TTL value is 1, it signifies that there is just one bounce to the next router. If that hop is the desired destination, everything is OK; the packet gets discarded. If TTL gets set to 10, the router will send the packet to ten hops, routers.


Set the TTL to 5 minutes at least 24 hours ahead of time if you intend to change your DNS. After making the changes, increase the TTL back to 24 hours. A 24-hour TTL get frequently advised. Deciphering the TTL is simple if you have a rudimentary grasp of networking.



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