network layer data plane Flashcards
network-layer protocol provides…
…logical-communication between hosts.
network-layer role and functuinalities
role:
transport segment from sending to receiving host
* sender: encapsulates segments into datagrams, passes to link layer
* receiver: delivers segments to transport layer protocol
functionalities:
- forwarding (move packets from a router’s input link to appropriate router output link, local action, implementer in hardware)
- routing ( determine route taken by packets from source to destination, network action, implemented in software)
which devices does Network-layer protocols affects
not only end systems but hosts and routers
network layer routers task
- Examine header fields in all IP datagrams passing through it
- Move datagrams from input ports to output ports to transfer datagrams along end-end path
Network layer division
- data plane (local, per-router function, determines how datagram arriving on
router input port is forwarded to router
output port) - control plane (network-wide logic, determines how datagram is routed among routers along end-end path from source host to destination host)
2 control-plane approaches
- traditional routing algorithms: implemented in routers (per-router control plane) (Each router has a routing component that communicates with the routing component of other routers)
- software-defined networking (SDN): implemented in (remote) servers (separate remote controller computes and distributes the forwarding tables to be used by each router)
network layer provides service
best-effort service.
rules for forwarding
- Destination-based forwarding
- Generalized-based forwarding
what is an IP address
It is a binary number that univocally identifies a network interface of a host or router.
Pay attention: it does not identify the host, one host can have multiple interfaces
strategies to decide When the buffer is full, which packet to drop?
- tail drop: drop arriving packet
- priority: drop/remove on priority basis
strategies to determine the order in which queued packets are transmitted over an outgoing link
- first come, first served (FIFO)
- priority-based
- round robin
- weighted fair queueing
- …
we have 1 IP address for each…
host or router interface (=connection between host/router and physical link),
router’s typically have multiple interfaces.
what is a subnet
device interfaces that can physically reach each other without passing through a router
IP address structure
- subnet part: devices in same subnet have
common high order bits - host part: remaining low order bits
How to get the IP address
1)The network administrator might first contact its ISP, which would provide addresses from a larger block of addresses that had already been allocated to the ISP.
2)Internet Corporation for Assigned Names and Numbers (ICANN): Global authority that has ultimate responsibility for managing the IP address space and allocating address blocks to ISPs and other organizations
- Once an organization has obtained a block of addresses, it can assign individual IP addresses to its host and router interfaces.
- Host addresses could be configured manually (very tedious). Better use Dynamic Host Configuration Protocol (DHCP).
- A network administrator can configure DHCP so that a given host receives the same IP address each time it connects to the network, or a host may be assigned a temporary IP address that will be different each time the host connects to the network.
- DHCP is a client-server protocol.
Network Address Translation (NAT)
NAT: all devices in local network share just one IPv4 address as far as outside world is concerned (this reduces the total number of IP addresses, Io e un mio amico e molto
probabile che abbiamo lo stesso IP sul computer perché siamo differenziati
dalla output port of the router che ha un IP diverso per noi 2)
IP Tunneling and encapsulation
IPv6 is embedded in ipv4
payload only if the router is old
and doesn’t support IPv6 (I hide an ipv6 in the payload of a ipv4)
what is hop limit
how many routers our datagram can pass through before being descarded
Generalized Forwarding and SDN
SDN =Software-defined networking
Generalized forwarding:
* many header fields can determine action
* many actions possible: drop/copy/modify/log packet
