Network Layer Flashcards
transport segment from sending to receiving host
Network layer
Two key network-layer
functions
forwarding
routing
three types of switching fabrics
memory
bus
crossbar
cyclically scan class queues, sending one
complete packet from each class
Round Robin (RR) scheduling:
priority scheduling:
send highest priority
queued packet
discard policy:if packet arrives to full queue: who to discard?
tail drop: drop arriving packet
priority: drop/remove on priority basis
random: drop/remove randomly
connection between
host/router and physical link
interface:
The address in a block must be
The first address must be evenly divisible by the
number of addresses.
power of 2
contiguous
*The first address in the block can be found by setting the rightmost
32 − n bits to
zero
*The last address in the block can be found by setting the rightmost
32 − n bits to
1s
*The last address in the block can be found by setting the rightmost
32 − n bits to
2^32−n.
Three-Levels Hierarchy: Subnetting
The organization has its own mask : network mask
Each subnet must also have its own mask: subnet mask
all routers have complete
topology, link cost info
centralized (global)
how does an ISP get block of addresses?
ICANN: Internet Corporation for Assigned
Names and Numbers
router knows physicallyconnected neighbors, link
costs to neighbors
decentralized
routing among hosts, routers
in same AS
intra-AS routing
Intra-AS Routing
also known as
interior gateway protocols (IGP)
is an intradomain routing protocol used inside an
autonomous system. It is based on Distance vector routing.
RIP
is an intradomain routing protocol used inside an
autonomous system uses link-state algorithm publicly available topology map at each node
OSPF (Open Shortest Path First)
inter-domain
routing protocol, it is the protocol that glues the
thousands of ISPs in the Internet together.
called Border Gateway Protocol, known as
BGP.
Obtain subnet reachability information from
neighboring ASs. BGP session that spans two ASs
is called
external BGP (eBGP) session.
used by hosts & routers to
communicate networklevel information
ICMP: internet control message protocol
Propagate reachability information to all AS-internal
routers. BGP session between routers in the same
AS is called an
internal BGP (iBGP) session.
BGP route selection
local preference value attribute
shortest AS-PATH
closest NEXT-HOP router
