network layer Flashcards
what is the network layer
transport seg from sender to receiver
- send side: encapsulates seg into datagram
- net layer protocols in every host, router
- router examines header field
2 key net layer principles
addressing, link layer independence
what is link layer independence
services provided does not depend on internal organization of the underlying datalink layers
what is addressing
each net layer entity is identified by net layer address
What are the two net layer planes
control
data
what control plane used for
compute and install routing tables on routers - needs to understand entire network that host is part of - network wide logic
what is data plane used for
local -per router - used by hosts and routers to create and process packets that contain user data - transform to transport packet
two key net layer functions
routing, forwarding
what is routing
determine route taken by packets using routing algos
what is forwarding
move packets from router inp to router out
describe the interplay between routinng and forwarding
routing algo determines end-end path through network, forwarding table determines local forwarding for this router
describe IP fragmentation and reassembly
network links have Max Transfer Size which is the largest possible link-level frame
large IP datagram fragmented within the net
- one DGram becomes several
-reassembled at final dest
- IP header bits identify and order fragments
name and explain 2 network layer service models
Datagram network - connectionless service
Virtual circuit - connection service
difference between DG network/virtual circuit vs UDP/TCP
service - host to host
no choice in which service is used - implemented in network core
What are some properties of datagram networks
- no call setup at net layer
- pkt contains src and dest host addresss plus data
- routers: no state about end-to-end connections (hop by hop forwarding)
- pkts forwarded using dest host address
what is IP address
32 bit identifier for host, router interface
what is an interface
connection between host/router and physical link - routers have multiple interface, hosts typically have one or two interfaces (e.g. ethernet, wifi 802.111)
what is a subnet
device interfaces with same same subnet part of the ip address - can physically reach each other without intervening router
how to change subnet sizes - explain what happens when you change the size of the host part of the IP address
increase host part - fewer subnets - more hosts in each subnet
decrease - smaller subnets - less hosts - more subnets
where do ISPs get addresses?
ICANN - internet corporation for assigned names and numbers - allocate addresses and manage DNS
motivation for IPv6
32 bit addresses run out
header format helps speed processing/forwarding
header changes to facilitate QoS
IPv6 header format
fixed length - 40byte
no fragmentation
128 bit address space
IPv6 header changes from IPv4
- priority
- flow label - identify DG in same flow
- next header - identify upper layer protocol for data
- no checksum
- options are outside of header - indicated by next header field
- ICMPv6
- additional message types - pkt too big
- multicast group management functions
what is tunneling?
IPv6 datagram carried as payload in IPv4 DG among IPv4 routers
