SUBJECT MARKING POINTS:
Internal:
• Student’s computer uses subnet mask (and destination/web server’s IP address) to determine if destination computer/web server is on same subnet // identify not on same subnet
• Up to two marks from description (in separate section below) of how subnet mask is used
• Packet is sent (from student’s computer) to Router (1)
• Router 1 identifies that destination is outside the LAN so forwards packet to router 3/router connected to Internet A gateway connected to Internet
External:
• Hierarchical organisation of routers
• Example of hierarchical organisation of routers eg passed up to a national router, transferred internationally and then passed back down a hierarchy
• Path to take selected by each router (not determined at start) NE. passed from router to router
• Route may change as a result of eg congestion, technical problems
Either:
• (Possible) repackaging of packet to use different protocol
• Route determined using the (Network ID part of the destination) IP address (Note: can infer "IP address" if just "address" is stated, if previously candidate has written about an IP address)
• Use of router tables / criteria to determine next hop / (step of) path
• Router decrementing "time to live" of packet
• Source and destination MAC addresses changed at each router // MAC addresses used for each “hop”
How subnet mask used (MAX 2 points):
• AND operation of subnet mask with student’s computer’s IP address
• AND operation of subnet mask with web server’s IP address
• Result (of AND operation) is the network ID
• Network IDs compared
• If they are the same, then the computers are on the same subnet
A. Interchangeable use of subnet ID and network ID