![]() Any tunneling solution that does not terminate at the endpoint PC, may cause MTU issues and lead to packet fragmentation. These could be GRE, IPsec tunnel or MPLS – you name it. Commonly, people face MTU issues when they run tunneling technologies on top of Ethernet with its default MTU value of 1500. Your Ethernet network may function perfectly, until the day you decide to “virtualize” networking resources. The default value is usually OK when transported across Internet, since most (read: good) ISPs support user-side MTU of 1500. Even while modern equipment enjoys jumbo GigabitEthernet frames of more than 9Kbyte in size, by default you commonly see MTU set to 1500 bytes everywhere. This means you commonly expect to see endpoint MTU values of at least 1500 bytes. Nowadays, most of end-user connections are Ethernet-based. Endpoints may only know about their local MTU settings, but not about the minimum MTU along the path (although an MTU discovery procedure exists). Unfortunately, there are cases when using IPv4 fragmentation is unavoidable.įragmentation occurs when you have MTU mismatch on the path between two communicating endpoints. Due to all these reasons, you may want to avoid fragmentation at all and/or ensure your network is insulated from fragmented packets. In addition to that, traffic fragmentation is used in numerous network attacks, allowing an attacker to bypass firewalls or IDSes in some situations. TCP needs to re-send the whole packet on a single fragment loss). Not only it increases the load on router CPUs, but also impacts applications performance (e.g. ![]() Fragmented IPv4 traffic may cause you a lot of problems in real life.
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