IT 347 Midterm 2 Review
Vocab Review
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ATM
CBR
ABR
VBR
UBR
MSS
MTU
AIMD
TCP: retransmission scenarios
Host A
X
loss
Sendbase
= 100
SendBase
= 120
SendBase
= 100
time
SendBase
= 120
time
lost ACK scenario
Host B
Seq=92 timeout
Host B
Seq=92 timeout
timeout
Host A
Transport Layer
premature timeout
3-3
TCP retransmission scenarios (more)
timeout
Host A
Host B
X
loss
SendBase
= 120
time
Cumulative ACK scenario
Transport Layer
3-4
TCP ACK generation [RFC 1122, RFC 2581]
Event at Receiver
TCP Receiver action
Arrival of in-order segment with
expected seq #. All data up to
expected seq # already ACKed
Delayed ACK. Wait up to 500ms
for next segment. If no next segment,
send ACK
Arrival of in-order segment with
expected seq #. One other
segment has ACK pending
Immediately send single cumulative
ACK, ACKing both in-order segments
Arrival of out-of-order segment
higher-than-expect seq. # .
Gap detected
Immediately send duplicate ACK,
indicating seq. # of next expected byte
Arrival of segment that
partially or completely fills gap
Immediate send ACK, provided that
segment starts at lower end of gap
Transport Layer
3-5
Fast Retransmit
• time-out period often
relatively long:
– long delay before resending
lost packet
• detect lost segments via
duplicate ACKs.
– sender often sends many
segments back-to-back
– if segment is lost, there will
likely be many duplicate ACKs
for that segment
• If sender receives 3 ACKs
for same data, it assumes
that segment after ACKed
data was lost:
– fast retransmit: resend
segment before timer
expires
Transport Layer
3-6
Host A
seq # x1
seq # x2
seq # x3
seq # x4
seq # x5
Host B
X
ACK x1
ACK x1
ACK x1
ACK x1
timeout
triple
duplicate
ACKs
time
Transport Layer
3-7
Fast retransmit algorithm:
event: ACK received, with ACK field value of y
if (y > SendBase) {
SendBase = y
if (there are currently not-yet-acknowledged segments)
start timer
}
else {
increment count of dup ACKs received for y
if (count of dup ACKs received for y = 3) {
resend segment with sequence number y
}
a duplicate ACK for
already ACKed segment
fast retransmit
Transport Layer
3-8
TCP Flow Control
flow control
sender won’t overflow
receiver’s buffer by
transmitting too much,
too fast
• receive side of TCP
connection has a receive
buffer:
IP
datagrams
(currently)
unused buffer
space
TCP data
(in buffer)
application
process
• speed-matching service:
matching send rate to
receiving application’s
drain rate
 app process may be slow
at reading from buffer
Transport Layer
3-9
TCP Flow control: how it works
IP
datagrams
(currently)
unused buffer
space
TCP data
(in buffer)
application
process
rwnd
RcvBuffer
(suppose TCP receiver discards
out-of-order segments)
• unused buffer space:
• receiver: advertises
unused buffer space by
including rwnd value in
segment header
• sender: limits # of
unACKed bytes to rwnd
– guarantees receiver’s buffer
doesn’t overflow
= rwnd
= RcvBuffer-[LastByteRcvd LastByteRead]
Transport Layer
3-10
TCP congestion control: bandwidth probing
 “probing for bandwidth”: increase transmission rate on
receipt of ACK, until eventually loss occurs, then decrease
transmission rate

continue to increase on ACK, decrease on loss (since available
bandwidth is changing, depending on other connections in network)
ACKs being received,
so increase rate
X loss, so decrease rate
sending rate
X
X
X
TCP’s
“sawtooth”
behavior
X
time
 Q: how fast to increase/decrease?
 details to follow
Transport Layer
3-11
TCP Congestion Control: details
• sender limits rate by limiting number of
unACKed bytes “in pipeline”:
LastByteSent-LastByteAcked  cwnd
– cwnd: differs from rwnd (how, why?)
– sender limited by min(cwnd,rwnd)
• roughly,
cwnd
bytes
cwnd
bytes/sec
• cwnd is dynamic,RTT
function of perceived
rate =
network congestion
RTT
ACK(s)
Transport Layer
3-12
TCP Congestion Control: more details
segment loss event: reducing
cwnd
• timeout: no response from
receiver
ACK received: increase cwnd
 slowstart phase:

– cut cwnd to 1
increase exponentially fast
(despite name) at connection
start, or following timeout
 congestion avoidance:
 increase linearly
• 3 duplicate ACKs: at least
some segments getting
through (recall fast
retransmit)
– cut cwnd in half, less
aggressively than on timeout
Transport Layer
3-13
TCP Slow Start
Transport Layer
Host A
Host B
RTT
• when connection begins, cwnd = 1
MSS
– example: MSS = 500 bytes &
RTT = 200 msec
– initial rate = 20 kbps
• available bandwidth may be >>
MSS/RTT
– desirable to quickly ramp up to
respectable rate
• increase rate exponentially until
first loss event or when threshold
reached
– double cwnd every RTT
– done by incrementing cwnd by
1 for every ACK received
time
3-14
Transitioning into/out of slowstart
ssthresh: cwnd threshold maintained by TCP
• on loss event: set ssthresh to cwnd/2
– remember (half of) TCP rate when congestion last occurred
• when cwnd >= ssthresh: transition from slowstart to congestion avoidance
phase
duplicate ACK
dupACKcount++
L
cwnd = 1 MSS
ssthresh = 64 KB
dupACKcount = 0
timeout
ssthresh = cwnd/2
cwnd = 1 MSS
dupACKcount = 0
retransmit missing segment
slow
start
new ACK
cwnd = cwnd+MSS
dupACKcount = 0
transmit new segment(s),as allowed
cwnd > ssthresh
L
timeout
ssthresh = cwnd/2
cwnd = 1 MSS
dupACKcount = 0
retransmit missing segment
Transport Layer
congestion
avoidance
3-15
TCP: congestion avoidance
• when cwnd > ssthresh
grow cwnd linearly
– increase cwnd by 1
MSS per RTT
– approach possible
congestion slower than
in slowstart
– implementation: cwnd
= cwnd +
MSS/cwnd for each
ACK received
Transport Layer
AIMD
 ACKs: increase cwnd by 1
MSS per RTT: additive
increase
 loss: cut cwnd in half
(non-timeout-detected
loss ): multiplicative
decrease
AIMD: Additive Increase
Multiplicative Decrease
3-16
TCP congestion control FSM: overview
cwnd > ssthresh
slow
start
loss:
timeout
loss:
timeout
loss:
timeout
loss:
3dupACK
congestion
avoidance
new ACK
loss:
3dupACK
fast
recovery
Transport Layer
3-17
TCP congestion control FSM: details
duplicate ACK
dupACKcount++
L
cwnd = 1 MSS
ssthresh = 64 KB
dupACKcount = 0
slow
start
timeout
ssthresh = cwnd/2
cwnd = 1 MSS
dupACKcount = 0
retransmit missing segment
dupACKcount == 3
ssthresh= cwnd/2
cwnd = ssthresh + 3
retransmit missing segment
new ACK
cwnd = cwnd+MSS
dupACKcount = 0
transmit new segment(s),as allowed
cwnd > ssthresh
L
timeout
ssthresh = cwnd/2
cwnd = 1 MSS
dupACKcount = 0
retransmit missing segment
timeout
ssthresh = cwnd/2
cwnd = 1
dupACKcount = 0
retransmit missing segment
new ACK
cwnd = cwnd + MSS (MSS/cwnd)
dupACKcount = 0
transmit new segment(s),as allowed
.
congestion
avoidance
duplicate ACK
dupACKcount++
New ACK
cwnd = ssthresh
dupACKcount = 0
dupACKcount == 3
ssthresh= cwnd/2
cwnd = ssthresh + 3
retransmit missing segment
fast
recovery
duplicate ACK
cwnd = cwnd + MSS
transmit new segment(s), as allowed
Transport Layer
3-18
Popular “flavors” of TCP
cwnd window size (in
segments)
TCP Reno
ssthresh
ssthresh
TCP Tahoe
Transmission round
Transport Layer
3-19
Summary: TCP Congestion Control
• when cwnd < ssthresh, sender in slow-start phase,
window grows exponentially.
• when cwnd >= ssthresh, sender is in congestionavoidance phase, window grows linearly.
• when triple duplicate ACK occurs, ssthresh set to
cwnd/2, cwnd set to ~ ssthresh
• when timeout occurs, ssthresh set to cwnd/2, cwnd
set to 1 MSS.
Transport Layer
3-20
TCP Futures: TCP over “long, fat pipes”
• example: 1500 byte segments, 100ms RTT, want 10 Gbps
throughput
• requires window size W = 83,333 in-flight segments
• throughput in terms of loss rate:
1.22  MSS
• ➜ L = 2·10-10 Wow RTT L
• new versions of TCP for high-speed
Transport Layer
3-21
TCP Fairness
fairness goal: if K TCP sessions share same bottleneck link of
bandwidth R, each should have average rate of R/K
TCP connection 1
TCP
connection 2
bottleneck
router
capacity R
Transport Layer
3-22
Why is TCP fair?
Two competing sessions:
• Additive increase gives slope of 1, as throughout increases
• multiplicative decrease decreases throughput proportionally
R
equal bandwidth share
loss: decrease window by factor of 2
congestion avoidance: additive increase
loss: decrease window by factor of 2
congestion avoidance: additive increase
Connection 1 throughput
Transport Layer
R
3-23
Fairness (more)
Fairness and UDP
• multimedia apps often do
not use TCP
– do not want rate throttled
by congestion control
• instead use UDP:
– pump audio/video at
constant rate, tolerate
packet loss
Fairness and parallel TCP
connections
• nothing prevents app from
opening parallel connections
between 2 hosts.
• web browsers do this
• example: link of rate R
supporting 9 connections;
– new app asks for 1 TCP, gets rate
R/10
– new app asks for 11 TCPs, gets
R/2 !
Transport Layer
3-24
Chapter 3: Summary
• principles behind transport layer
services:
– multiplexing, demultiplexing
– reliable data transfer
– flow control
– congestion control
• instantiation and implementation
in the Internet
– UDP
– TCP
Transport Layer
Next:
• leaving the network
“edge” (application,
transport layers)
• into the network
“core”
3-25
Interplay between routing and forwarding
routing algorithm
local forwarding table
header value output link
0100
0101
0111
1001
3
2
2
1
value in arriving
packet’s header
0111
1
3 2
Network Layer
4-26
Connection setup
• 3rd important function in some network architectures:
– ATM, frame relay, X.25
• before datagrams flow, two end hosts and intervening routers
establish virtual connection
– routers get involved
• network vs transport layer connection service:
– network: between two hosts (may also involve
intervening routers in case of VCs)
– transport: between two processes
Network Layer
4-27
Network service model
Q: What service model for “channel” transporting
datagrams from sender to receiver?
example services for
individual datagrams:
• guaranteed delivery
• guaranteed delivery with
less than 40 msec delay
example services for a flow
of datagrams:
• in-order datagram
delivery
• guaranteed minimum
bandwidth to flow
• restrictions on changes in
inter-packet spacing
Network Layer
4-28
Network layer service models:
Network
Architecture
Internet
Service
Model
Guarantees ?
Congestion
Bandwidth Loss Order Timing feedback
best effort none
ATM
CBR
ATM
VBR
ATM
ABR
ATM
UBR
constant
rate
guaranteed
rate
guaranteed
minimum
none
no
no
no
yes
yes
yes
yes
yes
yes
no
yes
no
no (inferred
via loss)
no
congestion
no
congestion
yes
no
yes
no
no
Network Layer
4-29
VC implementation
a VC consists of:
1. path from source to destination
2. VC numbers, one number for each link along
path
3. entries in forwarding tables in routers along path
• packet belonging to VC carries VC number
(rather than dest address)
• VC number can be changed on each link.
– New VC number comes from forwarding table
Network Layer
4-30
VC Forwarding
VC number
table
22
12
1
3
interface
number
Forwarding table in
northwest router:
Incoming interface Incoming VC #
1
2
3
1
…
2
32
12
63
7
97
…
Outgoing interface Outgoing VC #
3
1
2
3
…
22
18
17
87
…
Routers maintain connection state information!
Network Layer
4-31
Virtual circuits: signaling protocols
• used to setup, maintain teardown VC
• used in ATM, frame-relay, X.25
• not used in today’s Internet
application
5. Data flow begins
transport
network 4. Call connected
1. Initiate call
data link
physical
application
transport
3. Accept call
network
2. incoming call
data link
physical
6. Receive data
Network Layer
4-32
Datagram networks
• no call setup at network layer
• routers: no state about end-to-end connections
– no network-level concept of “connection”
• packets forwarded using destination host address
– packets between same source-dest pair may take different paths
application
transport
network
data link
physical
application
transport
network
2. Receive data
data link
physical
1. Send data
Network Layer
4-33
Datagram Forwarding
table
4 billion IP addresses, so
rather than list individual
destination address
list range of addresses
(aggregate table entries)
routing algorithm
local forwarding table
dest address output link
address-range 1
address-range 2
address-range 3
address-range 4
3
2
2
1
IP destination address in
arriving packet’s header
1
3 2
Network Layer
4-34
Datagram Forwarding table
Destination Address Range
Link Interface
11001000 00010111 00010000 00000000
through
11001000 00010111 00010111 11111111
0
11001000 00010111 00011000 00000000
through
11001000 00010111 00011000 11111111
1
11001000 00010111 00011001 00000000
through
11001000 00010111 00011111 11111111
2
otherwise
3
Q: but what happens if ranges don’t divide up so nicely?
Network Layer
4-35
Longest prefix matching
Longest prefix matching
when looking for forwarding table entry for given destination
address, use longest address prefix that matches destination
address.
Destination Address Range
Link interface
11001000 00010111 00010*** *********
0
11001000 00010111 00011000 *********
1
11001000 00010111 00011*** *********
2
otherwise
3
Examples:
DA: 11001000 00010111 00010110 10100001
Which interface?
DA: 11001000 00010111 00011000 10101010
Which interface?
Network Layer
4-36
Datagram or VC network: why?
Internet (datagram)
ATM (VC)
• data exchange among computers
– “elastic” service, no strict
timing req.
• “smart” end systems (computers)
– can adapt, perform control,
error recovery
– simple inside network,
complexity at “edge”
• many link types
– different characteristics
– uniform service difficult
• evolved from telephony
• human conversation:
– strict timing, reliability
requirements
– need for guaranteed
service
• “dumb” end systems
– telephones
– complexity inside network
Network Layer
4-37
IP Fragmentation and Reassembly
Example
 4000 byte datagram
 MTU = 1500 bytes
1480 bytes in
data field
offset =
1480/8
length ID
=4000 =x
fragflag
=0
offset
=0
One large datagram becomes
several smaller datagrams
length ID
=1500 =x
fragflag
=1
offset
=0
length ID
=1500 =x
fragflag
=1
offset
=185
length ID
=1040 =x
fragflag
=0
offset
=370
Network Layer
4-38
Subnets
223.1.1.2
223.1.1.1
How many?
223.1.1.4
223.1.1.3
223.1.9.2
223.1.7.0
223.1.9.1
223.1.7.1
223.1.8.1
223.1.8.0
223.1.2.6
223.1.2.1
223.1.3.27
223.1.2.2
Network Layer
223.1.3.1
223.1.3.2
4-39
IP addressing: CIDR
CIDR: Classless InterDomain Routing
– subnet portion of address of arbitrary length
– address format: a.b.c.d/x, where x is # bits in
subnet portion of address
host
part
subnet
part
11001000 00010111 00010000 00000000
200.23.16.0/23
Network Layer
4-40
DHCP client-server scenario
A
223.1.2.1
DHCP
server
223.1.1.1
223.1.1.2
223.1.1.4
223.1.2.9
B
223.1.2.2
223.1.1.3
223.1.3.1
223.1.3.27
223.1.3.2
Network Layer
E
arriving DHCP
client needs
address in this
network
4-41
DHCP: example
DHCP
UDP
IP
Eth
Phy
DHCP
DHCP
DHCP
DHCP
DHCP
DHCP
DHCP
DHCP
DHCP
DHCP
UDP
IP
Eth
Phy
•
connecting laptop needs its IP
address, addr of first-hop
router, addr of DNS server: use
DHCP

DHCP request encapsulated in
UDP, encapsulated in IP,
encapsulated in 802.1 Ethernet

Ethernet frame broadcast (dest:
FFFFFFFFFFFF) on LAN, received at
router running DHCP server

Ethernet demuxed to IP
demuxed, UDP demuxed to
DHCP
168.1.1.1
router
(runs DHCP)
Network Layer
4-42
DHCP: example
DHCP
UDP
IP
Eth
Phy
DHCP
DHCP
DHCP
DHCP
DHCP
DHCP
DHCP
DHCP
DHCP
DHCP
UDP
IP
Eth
Phy
•
DCP server formulates DHCP
ACK containing client’s IP
address, IP address of first-hop
router for client, name & IP
address of DNS server

encapsulation of DHCP server,
frame forwarded to client,
demuxing up to DHCP at client
client now knows its IP
address, name and IP address
of DSN server, IP address of its
first-hop router

router
(runs DHCP)
Network Layer
4-43
Hierarchical addressing: more specific routes
ISPs-R-Us has a more specific route to Organization 1
Organization 0
200.23.16.0/23
Organization 2
200.23.20.0/23
Organization 7
.
.
.
.
.
.
Fly-By-Night-ISP
“Send me anything
with addresses
beginning
200.23.16.0/20”
Internet
200.23.30.0/23
ISPs-R-Us
Organization 1
200.23.18.0/23
Network Layer
“Send me anything
with addresses
beginning 199.31.0.0/16
or 200.23.18.0/23”
4-44
NAT: Network Address Translation
NAT translation table
WAN side addr
LAN side addr
2: NAT router
changes datagram
source addr from
10.0.0.1, 3345 to
138.76.29.7, 5001,
updates table
1: host 10.0.0.1
sends datagram to
128.119.40.186, 80
138.76.29.7, 5001 10.0.0.1, 3345
……
……
S: 10.0.0.1, 3345
D: 128.119.40.186, 80
10.0.0.1
1
2
S: 138.76.29.7, 5001
D: 128.119.40.186, 80
138.76.29.7
S: 128.119.40.186, 80
D: 138.76.29.7, 5001
3: Reply arrives
dest. address:
138.76.29.7, 5001
3
10.0.0.4
S: 128.119.40.186, 80
D: 10.0.0.1, 3345
10.0.0.2
4
10.0.0.3
4: NAT router
changes datagram
dest addr from
138.76.29.7, 5001 to 10.0.0.1, 3345
Network Layer
4-45
Comparison of LS and DV algorithms
Message complexity
• LS: with n nodes, E links, O(nE)
msgs sent
• DV: exchange between neighbors
only
– convergence time varies
Speed of Convergence
• LS: O(n2) algorithm requires O(nE)
msgs
– may have oscillations
• DV: convergence time varies
– may be routing loops
– count-to-infinity problem
Robustness: what happens if
router malfunctions?
LS:
– node can advertise incorrect
link cost
– each node computes only its
own table
DV:
Network Layer
– DV node can advertise
incorrect path cost
– each node’s table used by
others
• error propagate thru
network
4-46
Interconnected ASes
3c
3b
3a
AS3
2a
1c
1a
1d
2c
2b
AS2
1b
Intra-AS
Routing
algorithm
AS1
Inter-AS
Routing
algorithm
Forwarding
table
Network Layer
• forwarding table
configured by both intraand inter-AS routing
algorithm
– intra-AS sets entries for
internal dests
– inter-AS & intra-As sets
entries for external dests
4-47
Inter-AS tasks
• suppose router in AS1
receives datagram
destined outside of AS1:
– router should forward
packet to gateway
router, but which one?
AS1 must:
1. learn which dests are
reachable through AS2,
which through AS3
2. propagate this
reachability info to all
routers in AS1
job of inter-AS routing!
3c
3b
other
networks
3a
AS3
2c
1c
1a
AS1
1d
2a
1b
Network Layer
2b
other
networks
AS2
4-48
Example: Setting forwarding table in router 1d
• suppose AS1 learns (via inter-AS protocol) that subnet x
reachable via AS3 (gateway 1c) but not via AS2.
– inter-AS protocol propagates reachability info to all internal routers
• router 1d determines from intra-AS routing info that its interface
I is on the least cost path to 1c.
– installs forwarding table entry (x,I)
x
3c
3b
other
networks
3a
AS3
2c
1c
1a
AS1
1d
2a
1b
Network Layer
2b
other
networks
AS2
4-49
Example: Choosing among multiple ASes
• now suppose AS1 learns from inter-AS protocol that subnet
x is reachable from AS3 and from AS2.
• to configure forwarding table, router 1d must determine
which gateway it should forward packets towards for dest x
– this is also job of inter-AS routing protocol!
x
3c
3b
other
networks
3a
AS3
2c
1c
1a
AS1
2a
1d
1b
2b
other
networks
AS2
?
Network Layer
4-50
Example: Choosing among multiple ASes
• now suppose AS1 learns from inter-AS protocol that subnet
x is reachable from AS3 and from AS2.
• to configure forwarding table, router 1d must determine
towards which gateway it should forward packets for dest x.
– this is also job of inter-AS routing protocol!
• hot potato routing: send packet towards closest of two
routers.
Learn from inter-AS
protocol that subnet
x is reachable via
multiple gateways
Use routing info
from intra-AS
protocol to determine
costs of least-cost
paths to each
of the gateways
Hot potato routing:
Choose the gateway
that has the
smallest least cost
Network Layer
Determine from
forwarding table the
interface I that leads
to least-cost gateway.
Enter (x,I) in
forwarding table
4-51
Intra-AS Routing
• also known as Interior Gateway Protocols (IGP)
• most common Intra-AS routing protocols:
– RIP: Routing Information Protocol (DV)
– OSPF: Open Shortest Path First (LS)
– IGRP: Interior Gateway Routing Protocol (Cisco
proprietary)(LS)
Network Layer
4-52
BGP basics: distributing path information
• using eBGP session between 3a and 1c, AS3 sends prefix
reachability info to AS1.
– 1c can then use iBGP do distribute new prefix info to all routers in AS1
– 1b can then re-advertise new reachability info to AS2 over 1b-to-2a
eBGP session
• when router learns of new prefix, it creates entry for prefix in
its forwarding table.
eBGP session
3b
other
networks
3a
AS3
iBGP session
2c
1c
1a
AS1
1d
2a
1b
Network Layer
2b
other
networks
AS2
4-53
Path attributes & BGP routes
• advertised prefix includes BGP attributes
– prefix + attributes = “route”
• two important attributes:
– AS-PATH: contains ASs through which prefix advertisement has passed:
e.g., AS 67, AS 17
– NEXT-HOP: indicates specific internal-AS router to next-hop AS. (may
be multiple links from current AS to next-hop-AS)
• gateway router receiving route advertisement uses import
policy to accept/decline
– e.g., never route through AS x
– policy-based routing
Network Layer
4-54
BGP route selection
• router may learn about more than 1 route
to destination AS, selects route based on:
1. local preference value attribute: policy
decision
2. shortest AS-PATH
3. closest NEXT-HOP router: hot potato routing
4. additional criteria
Network Layer
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BGP messages
• BGP messages exchanged between peers over TCP connection
• BGP messages:
– OPEN: opens TCP connection to peer and
authenticates sender
– UPDATE: advertises new path (or withdraws old)
– KEEPALIVE: keeps connection alive in absence of
UPDATES; also ACKs OPEN request
– NOTIFICATION: reports errors in previous msg;
also used to close connection
Network Layer
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BGP routing policy
legend:
B
W
provider
network
X
A
customer
network:
C
Y



A,B,C are provider networks
X,W,Y are customer (of provider networks)
X is dual-homed: attached to two networks
 X does not want to route from B via X to C
 .. so X will not advertise to B a route to C
Network Layer
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BGP routing policy (2)
legend:
B
W
provider
network
X
A
customer
network:
C
Y



A advertises path AW to B
B advertises path BAW to X
Should B advertise path BAW to C?
 No way! B gets no “revenue” for routing CBAW since neither W nor C
are B’s customers
 B wants to force C to route to w via A
 B wants to route only to/from its customers!
Network Layer
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Why different Intra- and Inter-AS routing ?
Policy:
• Inter-AS: admin wants control over how its traffic routed, who
routes through its net.
• Intra-AS: single admin, so no policy decisions needed
Scale:
• hierarchical routing saves table size, reduced update traffic
Performance:
• Intra-AS: can focus on performance
• Inter-AS: policy may dominate over performance
Network Layer
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Chapter 4: summary
4. 1 Introduction
4.2 Virtual circuit and
datagram networks
4.3 What’s inside a router
4.4 IP: Internet Protocol
–
–
–
–
Datagram format
IPv4 addressing
ICMP
IPv6
4.5 Routing algorithms
– Link state
– Distance Vector
– Hierarchical routing
4.6 Routing in the Internet
– RIP
– OSPF
– BGP
4.7 Broadcast and multicast
routing
Network Layer
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