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76 lines
2.3 KiB
Markdown
76 lines
2.3 KiB
Markdown
---
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title: "19-network-layer-data-plane"
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aliases:
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tags:
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- cosc203
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- lecture
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---
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- transport layer messages are divided into segments
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- passed to network layer
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- sender: encapsulates segments into IP packets, passes to link layer
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- reciever: deliver segments to tranport layer protocol
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- sender and reciever are connected by multple routers
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- routers
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- examine header fields in all IP packets passing through it
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- moves IP packers from input ports to output ports to transfer packets along end-end path
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- network layer protocols
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- IP
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- internet control message protocol (ICMP)
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- use for troubleshooting type things
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# Forwarding
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forwarding
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- move packets from a routers input link to appropriate output link
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- local, per-router function
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- function in data plane
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routing
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- determine route taken by packets from source to destination
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- network-wide logic
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- function in control plane
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- chooses shortest path through routers
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# network layer service model
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best effort
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- try its best to deliver packet
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- does not guarantee successful delivery
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- transport layer provides reliability
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- no big deal if packet is lost
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- does not guarantee timing or order of delivery
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- each packet sent individually, possibly through different paths
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- does not guarantee bandwidth available
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- network layer uses packet switching which unlike socket switching does not reserve resources
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# Routers
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destination-based forwarding: foward based only on destination IP address
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input port queueing: if datagrams arrive faster than fowarding rate into switch fabric
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# IP addressing
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- unreliable host-to-host communication protocol
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- datagram formatting, IP addressing, packet switching
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- ver: IP protocol versin number
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- head len: header length in bytes
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- type of service: diffserv(0:5) or ECN (6:7)
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- length: total datagram length (bytes)
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- time to live: remaining max hops (decremented at each router)
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- upper layer: which protocol use at transport layer
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- 16-bit id, flgs, fragment offset: fragmentation/reassembly
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- header checksum
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- source IP
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- destination IP
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- options: e.g., timestamp, record route taken
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overhead:
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- 20 bytes TCP
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- 20 bytes IP
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- = 40 bytes
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# IPv6 |