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Link Layer & Network Layer
Some slides are from lectures by Nick Mckeown, Ion Stoica, Frans Kaashoek, Hari Balakrishnan, and Sam Madden
Prof. Dina Katabi
Chapter 7.C and 7.D
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Previous Lecture
The network is organized into layers
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This Lecture
Link Layer Network Layer
Forwarding Routing Hierarchical Addressing and Routing
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Link Layer
Problem: Deliver data from one end of the link to the other
Need to address: Bits Analog Bits Framing Errors Medium Access Control (The Ethernet Paper)
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This Lecture
Link Layer Network Layer
Forwarding Routing Hierarchical Addressing and Routing
![Page 6: 1 Link Layer & Network Layer Some slides are from lectures by Nick Mckeown, Ion Stoica, Frans Kaashoek, Hari Balakrishnan, and Sam Madden Prof. Dina Katabi](https://reader030.vdocuments.net/reader030/viewer/2022032800/56649d405503460f94a19870/html5/thumbnails/6.jpg)
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The Internet Protocol (IP)
App
Transport
Network
Link
TCP / UDP
IP
Data Hdr
Data Hdr
TCP packet
IP packet
Protocol Stack
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The IP Header
Flags
vers
TTL
TOS
checksum
HLen Total Length
ID FRAG Offset
Protocol
SRC IP Address
DST IP Address
(OPTIONS) (PAD)
Hop count
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Network Layer: finds a path to the destination and forwards packets along that path
Difference between routing and forwarding Routing is finding the path Forwarding is the action of sending the packet to the
next-hop toward its destination
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Forwarding In a Router
RLink 1
Link 2
Link 3
Link 4
Link 1, ingress Link 1, egress
Link 2, ingress Link 2, egress
Link 3, ingress Link 3, egress
Link 4, ingress Link 4, egress
ChooseEgress
ChooseEgress
ChooseEgress
ChooseEgress
dst
dst
dst is via “4”dst is
via “4”
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This Lecture
Link Layer Network Layer
Forwarding Routing Hierarchical Addressing & Routing
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The Routing Problem: Generate forwarding tables
A D
C
B
E1 1 2 1
1
1
2
23
3
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Questions About Path Vector
How do we ensure no loops?
What happens when a node hears multiple paths to the same destination?
What happens if the graph changes?
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Hierarchical Routing
Internet: collection of domains/networks Inside a domain: Route over a graph of routers Between domains: Route over a graph of domains Address: concatenation of “Domain Id”, “Node Id”
domain-1
domain-2
domain-3
Interior router
Border router