ip-routing.md (1127B)
1 +++ 2 title = 'IP routing' 3 +++ 4 5 ## IP routing 6 IP addresses have prefix and identifier: 7 - e.g. 10.0.0.1/24: 24 bits network identifier, rest host identifier 8 - also subnet mask notation: 255.255.255.0 9 10 Routers have tables like this for forwarding: 11 12 | Match | Action | 13 |----------------|--------| 14 | 122.38.42.0/24 | port-2 | 15 | 116.16.0.0/16 | port-1 | 16 | 139.70.8.0/24 | drop | 17 18 IPv4 packets have fields including: 19 - TOS: type of service -- two bits used for explicit congestion notification 20 - total length 21 - TTL: decreased by one when passing router, packet dropped when TTL is 0 22 - protocol: transport layer protocol (TCP, UDP) 23 24 Generating forwarding tables: 25 - in same domain: OSPF (link state) 26 - routers exchange link-state messages to learn topology 27 - each router runs Dijkstra's to compute shortest paths to other routers 28 - each router generates forwarding table based on shortest paths 29 - between domains: BGP (distance vector) 30 31 32 Traffic engineering: network engineering for performance evaluation and optimization 33 - multiprotocol label switching: add extra header with labels to let you manipulate forwarding