If the undeliverable datagram was generated on this host, a “host unreachable” or “network unreachable” error is normally returned to the application that generated the datagram. If none of the steps works, the datagram is undeliverable. Search the routing table for an entry labeled “default.” If found, send the packet to the indicated next-hop router.All the hosts on the destination network can be handled with this single routing table entry. If found, send the packet to the indicated next-hop router or to the directly connected interface. Search the routing table for an entry that matches just the destination network ID.Search the routing table for an entry that matches the complete destination IP address (matching network ID and host ID).IP routing performs the following actions IP routing provides the IP address of the next-hop router to which the data is sent and the next-hop router is assumed to be closer to destination. IP does not know the complete route to any destination (except directly connected). IP routing is done on a hop-by-hop basis. Various protocols used in routing are BGP (Border Gateway Protocol), IS-IS (Intermediate System – Intermediate System), OSPF (Open Shortest Path First) and RIP (Routing Information Protocol). The IP Routing protocols enable routers to build up a forwarding table to relate an final destination address with next hop addresses. However, an IP packet is often carried as the payload inside an Ethernet frame, which has its own header and trailer.ĭata packet is routed from source to destination by passing through one or more routers and networks. 32 bits that contain the destination address.Īfter those 160 bits, optional flags can be added of varied length, which can change as per protocol used, then data that packet carries is added.32 bits that contain the source IP address,.16 bits that contain the Header Checksum, a number used in error detection,.8 bits that contain the protocol (TCP, UDP, ICMP, etc.).8 bits that contain the Time to live (TTL), which is the number of hops (router, computer or device along a network) the packet is allowed to pass before it dies (for example, a packet with a TTL of 16 will be allowed to go across 16 routers to get to its destination before it is discarded),.13 bits that contain the fragment offset, a field to identify position of fragment within original packet. ![]() The first contains a zero, followed by a flag that says whether the packet is allowed to be fragmented or not (DF or Don’t fragment), and a flag to state whether more fragments of a packet follow (MF or More Fragments) 16 bits that contain an identification tag to help reconstruct the packet from several fragments,. ![]() ![]()
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