Committee Chair
Autonomous Networks Deborah Estrin
End-to-End Services Bob Braden
Internet Architecture Dave Mills
Internet Engineering Phil Gross
EGP2 Mike Petry
Name Domain Planning Doug Kingston
Gateway Monitoring Craig Partridge
Internic Jake Feinler
Performance & Congestion ControlRobert Stine
NSF Routing Chuck Hedrick
Misc. MilSup Issues Mike St. Johns
Privacy Steve Kent
IRINET Requirements Vint Cerf
Robustness & Survivability Jim Mathis
Scientific Requirements Barry Leiner
Note that under Internet Engineering, there are a set of task forces and chairs to look at short term concerns. The chairs of these task forces are not part of the IAB.
-9- Routing
Routing is the algorithm by which a network directs a packet from its source to its destination. To appreciate the problem, watch a small child trying to find a table in a restaurant. From the adult point of view the structure of the dining room is seen and an optimal route easily chosen. The child, however, is presented with a set of paths between tables where a good path, let alone the optimal one to the goal is not discernible.***
A little more background might be appropriate. IP gateways (more correctly routers) are boxes which have connections to multiple networks and pass traffic between these nets. They decide how the packet is to be sent based on the information in the IP header of the packet and the state of the network. Each interface on a router has an unique address appropriate to the network to which it is connected. The information in the IP header which is used is primarily the destination address. Other information (e.g. type of service) is largely ignored at this time. The state of the network is determined by the routers passing information among themselves. The distribution of the database (what each node knows), the form of the updates, and metrics used to measure the value of a connection, are the parameters which determine the characteristics of a routing protocol.
Under some algorithms each node in the network has complete knowledge of the state of the network (the adult algorithm). This implies the nodes must have larger amounts of local storage and enough CPU to search the large tables in a short enough time (remember this must be done for each packet). Also, routing updates usually contain only changes to the existing information (or you spend a large amount of the network capacity passing around megabyte routing updates). This type of algorithm has several problems. Since the only way the routing information can be passed around is across the network and the propagation time is non-trivial, the view of the network at each node is a correct historical view of the network at varying times in the past. (The adult algorithm, but rather than looking directly at the dining area, looking at a photograph of the dining room. One is likely to pick the optimal route and find a bus-cart has moved in to block the path after the photo was taken). These inconsistencies can cause circular routes (called routing loops) where once a packet enters it is routed in a closed path until its time to live (TTL) field expires and it is discarded.
Other algorithms may know about only a subset of the network. To prevent loops in these protocols, they are usually used in a hierarchical network. They know completely about their own area, but to leave that area they go to one particular place (the default gateway). Typically these are used in smaller networks (campus, regional…).
-10-
Routing protocols in current use:
Static (no protocol-table/default routing)