![]() ![]() Because they have these chips doing the main job, they often just have a weak cpu to run the operating system, a management console and other not mission critical stuff. Because of that packet loss or high latence on a single hop is not an indicator for network problems, since the router is not required to send that response messages at all.Īs a side note: Internet routers are often specialised computers that have Application Specific Integrated Circuits (ASICs) doing all the forwarding (may also be called "hardware offloading") and other "router stuff" that is important. At this point the ping will reach the destination and a ping response (ICMP type 0) will be send back to you by the destination.Īs explained above, the TTL-Exceeded messages are not a priority for routers and some routers may just not send them at all. That is repeated again and again, every time with the TTL field increased by one, so you get the whole path step by step until the TTL is higher than the number of hops between you and your destination. And now you have the ip address of the second hop. That way your router will forward the packet, but the next hop will decrease the TTL to zero and send a TTL-Exceeded message to you. Then the same is done again, but with a TTL of 2. The traceroute program gets this response and with it the ip address of the first hop. ![]() To get the path between you and a destination (the traceroute), programs like pingplotter make use of the TTL field.Ī ping (ICMP type 8) is send to the destination, but the TTL is just set to 1, so the first hop (in most cases your router) will decrease the TTL to zero, drop the packet and send you a TTL-Exceeded message with its own ip as sender. For this type of messages (and also other stuff like pings), the Internet Control Message Protocol (ICMP) is used, in this particular case it would be a message of type 11 (Time Exceeded). The router is not required to inform the sender of the packet that it has been dropped, but if the router does send an information, it must be a TTL-Exceeded message. If a router decreases the value to zero, the packet will not be forwarded (it will be dropped) and therefore a potential circle is broken. That is the reason why packets contain a Time-To-Live (TTL) value, it is just a number that gets decreased each time a router forwards the packet (the router itself is not the destination) to the next hop. But somehow we must be able to stop packets that are just running in circles, because otherwise they would run there forever and bring the whole network down if enough of them accumulate. Routers have no idea which way a packet took to reach them (the route is not recorded), so no way to detect a circle. And even more bad, it can be send in circles. Since the internet is dynamic it can happen that a packet gets routed the wrong way and never reaches its destination. Since you probably have a default gateway (your router), it is a safe to guess that this will be your first hop. When you send a packet to a server, you have no idea of how many routers/hops are in between you and the destination. To give a full answer i will first explain how a traceroute (thats what pingplotter does) works. Their main goal is to forward packets to the next hop as fast as possible, everything else they only do if they have spare resources for it. In short: The answers to pings are not a priority for routers. u/RoweDent created this awesome resource on network theory u/tht1kidd_ has created a suggestion post regarding information everyone needs to provide when asking a question about their network There have been some excellent guides written in this sub, and we're always looking for more! If you wish for your flair to be changed, please message the mods and we'll be happy to change it for you. Proof of at least 6 month's history of posting in this subredditĪs a result of this, users are now no longer able to edit their own flair. ![]() Your highest level of industry certification, or highest IT related job title held in the last 5 years to a comment you made in the last 6 months, helping someone in the community ![]() To obtain trusted flair for your account please message the mods of /r/HomeNetworking with the following info Trusted user flair has been added as a means of verification that a user has a substantial knowledge of networking. Please flair your posts as Solved, Unsolved, or simply Advice. If you can't find what you're looking for with the search function please feel free to post a new question after reading the posting guidelines Please use the search function to look for keywords related to what you want to ask before posting since most common issues have been answered. ![]()
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