CSI 4321: TCP/IP Notes Chapter 5

How big must TTL be?

> numbr of hops between source and destination, otherwise packet loss.

A host with IP address 162.244.10.13/16 wants to send a packet to a host with IP address 162.244.189.32/16. Will it use direct or indirect routing? How do you know?

Direct delivery - both have same net id.

IP Routing Tables

Each host maintains a routing table: <Final Dest Address> <Next hop address> <Interface>

What is the advantage to only reassembling packet fragments at their final destination?

Improves speed, no guarentee fragments follow same route.

TCP/IP CH.5#10 A host with IP address 205.116.18.144/24 wants to send a packet to a host with IP address 205.116.19.100/24. Will it use direct or indirect routing? How do you know?

Indirect delivery - do not have same netid.

What is thee highest layer of the TCP/IP protocol stack that needs to be implemented on an IP router if it is only making forwarding decisions?

Networking layer, since IP header contains addresses the r outer uses fo rforwarding.

Direct Delivery

Occurs when source and destination hosts reside on the same local network. Netid of source address = netid of dest address. Determines hardware address of dest using ARP cache or ARP request.

View and manipulate a host's routing table

ip route

IP Packet fragmentation

Size of MTU on DLL protocol causes us o fragment packet into pieces small enough to fit into the MTU. Each fragment must be self-contained IP datagram so that it can be routed. 3 header fields: Identification, Flags, Fragment offset (in 8-byte units). Flags include: Don't fragment bit More Fragments bit

Indirect delivery

Source and destination do not reside on the same local network. Involves use of routers to direct the packet from source to destination. A series of direct deliveries that moves an IP packet closer to its final destination. As it is routed, the source and destination physical addresses change, but the IP addresses are fixed. Only things that change in the packet TTL and Checksum header

Why must both the TTL and Checksum fields be changed at each router?

TTL decremented at each hop. When TTL changes, IP header changes, so checksum also changees.