Download ppt - The Fengs

CSE524: Lecture 14
Network layer
Specific protocols (IP), network
devices
1
Administrative
• Reading assignment
– Chapter 4.1-4.7
• Homework #4 available
– See course web site
2
Where we’re at…
•
•
•
•
•
Internet architecture and history
Internet protocols in practice
Application layer
Transport layer
Network layer
– Network-layer functions
– Specific network layer protocols (IPv4)
• IP demux, IP security, IP fragmentation, IP addressing, etc.
• IP routing
– Who provides functionality? (Source-routing, virtual circuits, routers)
– IP route lookups, Internet area hierarchy, Specific IP routing protocols
– IPv6
– Network-layer devices
• Data-link layer
• Physical layer
3
IP routing
• Who provides functionality?
– Recall…
• Source routes
– Calculated by each host and attached to packet
– Network devices stateless
• Virtual circuits
– Setup by edge devices
– Network devices have simple lookup tables
• Network routers with global addressing….
4
NL: Network routers (Global IP addresses)
• Most prevalent way to route on the Internet
– Each packet has destination IP address
– Each router has forwarding table of..
• destination IP  next hop IP address
– Distributed routing algorithm for calculating
forwarding tables
5
NL: Global Address Example
Packet
R
R
2
Sender
1
R1
2
3
R2
1
4
R4
3
4
R3
R
2
1
R3
4
3
Receiver
R
R3
6
NL: Issues in Router Table Size
• One entry for every host on the Internet
– 100M entries,doubling every year
• One entry for every LAN
– Every host on LAN shares prefix
– Still too many, doubling every year
• One entry for every organization
– Every host in organization shares prefix
– Requires careful address allocation
– What constitutes an “organization”?
7
NL: Global Addresses
• Advantages
– Simple error recovery
• Disadvantages
– Every router knows about every destination
• Potentially large tables
– All packets to destination take same route
8
NL: Comparison
Source Routing
Global Addresses
Virtual Circuits
Header Size
Worst
OK – Large address
OK (larger than
global if IP
payload)
Router Table Size
None
Number of hosts
(prefixes)
Number of circuits
Forward Overhead
Best
Prefix matching
Good (table index)
Setup Overhead
None
None
Connection Setup
Tell all routers
Tell all routers,
Tear down circuit
and re-route
Error Recovery
Tell all hosts
9
NL: IP route lookups
• Original IP Route Lookup
– In the early days, address classes made it easy
• A: 0 | 7 bit network | 24 bit host (16M each)
• B: 10 | 14 bit network | 16 bit host (64K)
• C: 110 | 21 bit network | 8 bit host (255)
– Address would specify prefix for forwarding table
– Simple lookup
10
NL: Original IP Route Lookup – Example
• www.ogi.edu address 129.95.5.30
– Class B address – class + network is 129.95
– Lookup 129.95 in forwarding table
– Prefix – part of address that really matters for routing
• Forwarding table contains
– List of prefix entries
– A few fixed prefix lengths (8/16/24)
• Large tables
– 2 Million class C networks
– Sites with multiple class C networks have multiple route
entries at every router
11
NL: Getting a datagram from source to dest.
routing table in A
Dest. Net. next router Nhops
Classful routing example
IP datagram:
misc source dest
fields IP addr IP addr
data
• datagram remains
unchanged, as it travels
source to destination
• addr fields of interest
here
223.1.1
223.1.2
223.1.3
A
223.1.1.4
223.1.1.4
1
2
2
223.1.1.1
223.1.2.1
B
223.1.1.2
223.1.1.4
223.1.1.3
223.1.3.1
223.1.2.9
223.1.3.27
223.1.2.2
223.1.3.2
12
E
NL: Getting a datagram from source to dest.
misc
data
fields 223.1.1.1 223.1.1.3
Starting at A, given IP
datagram addressed to B:
• look up net. address of B
• find B is on same net. as A
• link layer will send datagram
directly to B inside link-layer
frame
– B and A are directly
connected
Dest. Net. next router Nhops
223.1.1
223.1.2
223.1.3
A
223.1.1.4
223.1.1.4
1
2
2
223.1.1.1
223.1.2.1
B
223.1.1.2
223.1.1.4
223.1.1.3
223.1.3.1
223.1.2.9
223.1.3.27
223.1.2.2
223.1.3.2
13
E
NL: Getting a datagram from source to dest.
misc
data
fields 223.1.1.1 223.1.2.3
Dest. Net. next router Nhops
223.1.1
223.1.2
223.1.3
Starting at A, dest. E:
– look up network address of E
– E on different network
• A, E not directly attached
– routing table: next hop router to
E is 223.1.1.4
– link layer sends datagram to
router 223.1.1.4 inside link-layer
frame
– datagram arrives at 223.1.1.4
– continued…..
A
223.1.1.4
223.1.1.4
1
2
2
223.1.1.1
223.1.2.1
B
223.1.1.2
223.1.1.4
223.1.1.3
223.1.3.1
223.1.2.9
223.1.3.27
223.1.2.2
223.1.3.2
14
E
NL: Getting a datagram from source to dest.
misc
data
fields 223.1.1.1 223.1.2.3
Arriving at 223.1.4, destined
for 223.1.2.2
– look up network address of E
– E on same network as router’s
interface 223.1.2.9
• router, E directly attached
– link layer sends datagram to
223.1.2.2 inside link-layer frame
via interface 223.1.2.9
– datagram arrives at 223.1.2.2!!!
(hooray!)
Dest.
next
network router Nhops interface
223.1.1
223.1.2
223.1.3
A
-
1
1
1
223.1.1.4
223.1.2.9
223.1.3.27
223.1.1.1
223.1.2.1
B
223.1.1.2
223.1.1.4
223.1.1.3
223.1.3.1
223.1.2.9
223.1.3.27
223.1.2.2
223.1.3.2
15
E
NL: IP route lookup and CIDR
• Recall Classless routing (CIDR)
– Advantages
• Saves space in route tables
• Makes more efficient use of address space
– ISP allocated 8 class C chunks, 201.10.0.0 to 201.10.7.255
– Allocation uses 3 bits of class C space
– Remaining 21 bits are network number, written as 201.10.0.0/21
– Replace 8 class C entries with 1 combined entry
• Routing protocols carry prefix length with destination network address
– But....Makes route lookup more complex
• No longer separate class A/B/C route tables each with O(1) lookup
• One table containing many prefix lengths
• Must match against all routes simultaneously via longest prefix match
16
NL: CIDR example
ISP X given 16 class C networks
200.23.16.* to 200.23.31.* (or 200.23.16/20)
Adjacent
ISP
router
1
1
ISP X
2
Route
200.23.16/20
Interface
1
Large
company
200.23.16.
0/21
200.23.16.0/24, 200.200.17.0/24
200.23.18.0/24, 200.200.19.0/24
200.23.20.0/24, 200.200.21.0/24
200.23.22.0/24, 200.200.23.0/24
3
4
Medium
company
200.23.24.0/
22
200.23.24.0/24
200.23.25.0/24
200.23.26.0/24
200.23.27.0/24
5
Route
200.23.16/21
200.23.24/22
200.23.28/23
200.23.30/24
Small
company
200.23.28.
0/23
200.23.28.0/24
200.23.29.0/24
Interface
2
3
4
5
Tiny
company
200.23.30.
0/24
17
NL: CIDR, hierarchical addressing, route aggregation
Hierarchical addressing allows efficient advertisement of routing
information:
Organization 0
200.23.16.0/23
Organization 1
200.23.18.0/23
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
“Send me anything
with addresses
beginning
199.31.0.0/16”
18
NL: Another CIDR example
• Routing to the network
10.1.1.2/31
10.1.1.3
• Packet to 10.1.1.3
arrives
• Path is R2 – R1 – H1
– H2
10.1.1.2
10.1.1.4
H1
H2
10.1.1/24
10.1.3.2
10.1.1.1
10.1.2.2
10.1.3.1
R1
H3
10.1.3/24
10.1.2/24
10.1.16/24
Provider
R2
10.1.8.1
10.1.2.1
10.1.16.1
10.1.8/24
H4
10.1.8.4
19
NL: Another CIDR example
• Subnet Routing
10.1.1.2/31
10.1.1.3
• Packet to 10.1.1.3
• Matches 10.1.0.0/22
10.1.1.2
10.1.1.4
H1
H2
10.1.1/24
10.1.3.2
10.1.1.1
10.1.2.2
10.1.3.1
R1
Routing table at R2
Destination
Next Hop
H3
10.1.3/24
Interface
127.0.0.1
127.0.0.1
lo0
Default or 0/0
provider
10.1.16.1
10.1.8.0/24
10.1.8.1
10.1.8.1
10.1.2.0/24
10.1.2.1
10.1.2.1
10.1.0.0/22
10.1.2.2
10.1.2.1
10.1.2/24
10.1.16/24
R2
10.1.8.1
10.1.2.1
10.1.16.1
10.1.8/24
H4
10.1.8.4
20
NL: Another CIDR example
• Subnet Routing
10.1.1.2/31
10.1.1.3
• Packet to 10.1.1.3
• Matches 10.1.1.2/31
10.1.1.2
10.1.1.4
H1
10.1.1/24
10.1.3.2
• Longest prefix match
10.1.1.1
10.1.2.2
10.1.3.1
R1
Routing table at R1
Destination
Next Hop
H2
H3
10.1.3/24
Interface
127.0.0.1
127.0.0.1
lo0
Default or 0/0
10.1.2.1
10.1.2.2
10.1.3.0/24
10.1.3.1
10.1.3.1
10.1.1.0/24
10.1.1.1
10.1.1.1
10.1.2.0/24
10.1.2.2
10.1.2.2
10.1.1.2/31
10.1.1.4
10.1.1.1
10.1.2/24
10.1.16/24
R2
10.1.8.1
10.1.2.1
10.1.16.1
10.1.8/24
H4
10.1.8.4
21
10.1.1.3 matches both routes, use longest prefix match
NL: Another CIDR example
• Subnet Routing
10.1.1.2/31
10.1.1.3
10.1.1.2
10.1.1.4
• Packet to 10.1.1.3
• Direct route
H1
H2
10.1.1/24
10.1.3.2
10.1.1.1
10.1.2.2
10.1.3.1
• Longest prefix match
R1
H3
10.1.3/24
Routing table at H1
10.1.2/24
10.1.16/24
Destination
Next Hop
Interface
127.0.0.1
127.0.0.1
lo0
Default or 0/0
10.1.1.1
10.1.1.4
10.1.1.0/24
10.1.1.4
10.1.1.4
10.1.1.2/31
10.1.1.2
10.1.1.2
R2
10.1.8.1
10.1.2.1
10.1.16.1
10.1.8/24
H4
10.1.8.4
22
10.1.1.3 matches both routes, use longest prefix match
NL: CIDR Shortcomings
• Customer selecting a new provider
– Renumbering required
199.31.0.0/16
201.10.0.0/21
Provider 1
201.10.0.0/22 201.10.4.0/24
201.10.5.0/24
Provider 2
201.10.6.0/23
23
NL: CIDR Shortcomings
• Multi-homing
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
“Send me anything
with addresses
beginning 199.31.0.0/16
or 200.23.18.0/23”
24
NL: Longest-prefix matching
• Algorithms and data structures for CIDR-based IP route lookups
– Ruiz-Sanchez, Biersack, Dabbous, “Survey and Taxonomy
of IP address Lookup Algorithms”, IEEE Network, Vol. 15,
No. 2, March 2001
•
•
•
•
•
•
•
•
•
•
Binary trie
Multi-bit trie
LC trie
Lulea trie
Full expansion/compression
Binary search on prefix lengths
Binary range search
Multiway range search
Multiway range trees
Binary search on hash tables (Waldvogel – SIGCOMM 97)
25
NL: Binary trie
• Data structure to support longest-prefix match for forwarding
• Bit-wise traversal from left-to-right
Route
A
B
C
D
E
F
G
H
I
Prefixes
0*
01000*
011*
1*
100*
1100*
1101*
1110*
1111*
0
1
A
D
1
0
0
1
0
C
0
1
0
1
E
0
1
0
1
F
G
H
I
0
26
B
NL: Path-compressed binary trie
• Eliminate single branch point nodes
• Compare address against all prefixes along path to leaf
– Take deepest match
• Variants include PATRICIA and BSD tries
Route
A
B
C
D
E
F
G
H
I
Prefixes
0*
01000*
011*
1*
100*
1100*
1101*
B
1110*
1111*
Bit=1
0
1
Bit=3 A
0
Bit=2 D
1
0
C
1
E
Bit=3
0
Bit=4
0
F
1
1
Bit=4
0
1
G
H
I
27
NL: Multi-bit tries
• Compare multiple bits at a time
– Stride = number of bits being examined
– Reduces memory accesses
– Increase memory required
• Forces table expansion for prefixes falling in between strides
– Two types
• Variable stride multi-bit tries
• Fixed stride multi-bit tries
• Most route entries are Class C
– Optimize “stride” based on this
28
NL: Variable stride multi-bit trie
• Single level has variable stride lengths
Route
A
B
C
D
E
F
G
H
I
Prefixes
0*
01000*
011*
1*
100*
A
1100*
1101*
1110*
1111*
00
01
10
11
A
00 01
D
0
10 11
C
C
E
D
1
00 01
F
G
10 11
H
I
0 1
B
29
NL: Fixed stride multi-bit trie
• Single level has equal strides
Route
A
B
C
D
E
F
G
H
I
Prefixes
0*
01000*
011*
1*
100*
000
1100*
1101*
A
1110*
1111*
001
A
010
011
A
C
B
00 01 10 11
100
101
E
110
D
111
D
D
F F G G H H I I
00 01 10 11 00 01 10 11
30
NL: Issues
• Scaling
– IPv6
• Stride choice
– Tuning stride to route table
– Bit shuffling
31
NL: Hierarchical routing in the Internet
• Area routing
– aggregate routers into
regions, “autonomous
systems” (AS)
– administrative autonomy
– routers in same AS run same
routing protocol
• “intra-AS” routing protocol
or interior gateway
protocol (IGP)
• routers in different AS can
run different intra-AS
routing protocol
gateway routers
• special routers in AS
• run intra-AS routing
protocol with all other
routers in AS
• also responsible for
routing to destinations
outside AS
– run inter-AS routing
protocol or exterior
gateway protocol
(EGP) with other
gateway routers in
other AS’s
32
NL: Example #1
1
2
IGP
2.1
IGP
EGP
1.1
2.2.1
1.2
EGP
EGP
EGP
3
IGP
4.1
EGP
5
3.1
5.1
2.2
IGP
IGP
4.2
4
3.2
5.2
33
NL: Example #2
C.b
a
C
Gateways:
B.a
A.a
b
A.c
d
A
a
b
c
a
c
B
b
•perform inter-AS
routing amongst
themselves
•perform intra-AS
routers with other
routers in their
AS
network layer
inter-AS, intra-AS
routing in
gateway A.c
link layer
physical layer
34
NL: Path Sub-optimality
1
2
2.1
1.1
2.2
2.2.1
1.2
1.2.1
start
end
3.2.1
3
3 hop red path
vs.
2 hop green path
3.1
3.2
35
NL: AS Categories
• Stub: an AS that has only a single connection to
one other AS - carries only local traffic.
• Multi-homed: an AS that has connections to
more than one AS, but does not carry transit
traffic
• Transit: an AS that has connections to more than
one AS, and carries both transit and local traffic
(under certain policy restrictions)
36
NL: AS categories example
AS1
AS3
AS1
AS2
AS1
AS3
AS2
Transit
Stub
AS2
Multi-homed
37
NL: Specific IP routing protocols
• Intra-AS routing protocols (interior routing
protocols)
–
–
–
–
GGP
RIP
IGRP
OSPF
• Inter-AS routing protocols (exterior routing
protocols)
– EGP
– BGP
38
NL: Intra-AS Routing
• Generate Intra-AS routing tables
• Also known as Interior Gateway Protocols (IGP)
• Most common IGPs
– Distance vector protocols
• GGP: Gateway-to-Gateway Protocol (1970s)
• RIP: Routing Information Protocol (1982)
• IGRP: Interior Gateway Routing Protocol (1988)
– Cisco proprietary
– Link state protocols
• OSPF: Open Shortest Path First
• Hierarchical OSPF
39
NL: RIP (Routing Information Protocol)
• Included in BSD-UNIX Distribution in 1982
• Distance metric: # of hops (max = 15 hops)
• Vectors exchanged every 30 sec and when triggered
– Static update period leads to synchronization problems
• Split horizon with poisonous reverse
• RIP-2 in 1993 adds prefix mask for CIDR
40
NL: RIP: Link Failure and Recovery
If no advertisement heard after 180 sec -->
neighbor/link declared dead
– routes via neighbor invalidated
– new advertisements sent to neighbors
– neighbors in turn send out new advertisements (if
tables changed)
– link failure info quickly propagates to entire net
– poison reverse used to prevent count-to-infinity
(infinite distance = 16 hops)
41
NL: RIP Table processing
• RIP routing tables managed by application-level process
called route-d (daemon)
• advertisements sent in UDP packets, periodically
repeated
42
NL: IGRP (Interior Gateway Routing Protocol)
• CISCO proprietary; successor of RIP (mid 80s)
–
–
–
–
Distance Vector, like RIP
several cost metrics (delay, bandwidth, reliability, load etc)
90 sec update with triggered updates
Split horizon
• V1: path holddown
• V2: route poisoning
• multiple path support
– uses TCP to exchange routing updates
– EIGRP
• Loop-free routing via DUAL (based on diffused
computation)
• CIDR support
43
NL: Intra-AS Link State Protocols
• OSPF
– Uses Link State algorithm
• LS packet dissemination
• Topology map at each node
• Route computation using Dijkstra’s algorithm
– OSPF advertisement carries one entry per neighbor router
– Advertisements disseminated to entire AS (via flooding)
44
NL: OSPF “advanced” features (not in RIP)
• Security: all OSPF messages authenticated (to
prevent malicious intrusion); TCP connections used
• Multiple same-cost paths allowed (only one path in
RIP)
• For each link, multiple cost metrics for different TOS
(eg, satellite link cost set “low” for best effort; high
for real time)
• Integrated uni- and multicast support:
– Multicast OSPF (MOSPF) uses same topology data base as
OSPF
• Hierarchical OSPF in large domains.
45
NL: Hierarchical OSPF
46
NL: Hierarchical OSPF
• Two-level hierarchy: local area, backbone.
– Link-state advertisements only in area
– each nodes has detailed area topology; only know
direction (shortest path) to nets in other areas.
• Area border routers: “summarize” distances to nets
in own area, advertise to other Area Border routers.
• Backbone routers: run OSPF routing limited to
backbone.
• Boundary routers: connect to other ASs.
47
NL: Inter-AS routing
• EGP
• BGP
48
NL: Why different Intra- and Inter-AS routing ?
Policy vs. Performance:
• Inter-AS
– ISPs want control over how its traffic routed, who routes
through its net
– policy and monetary factors dominate over performance
• Intra-AS
– single administrative policy
– performance dominates
49
NL: History
• Mid-80s: EGP (Exterior Gateway Protocol)
– Used in original ARPAnet
– Reachability protocol (no shortest path)
• Single bit for reachability information
– Topology restricted to a tree (no cycles allowed)
• ARPA-managed packet switches at top of tree
– Unacceptable once Internet grew to multiple
independent backbones
• Result: BGP development
50
NL: BGP
• Link state or distance vector?
– Problems with distance-vector:
• Bellman-Ford algorithm may not converge
– More problems with link state:
• Everyone sees every link
– LS database too large – entire Internet
– Can’t easily control who uses the network (i.e. an ISP may want to
hide particular links from being used by others, but link states are
broadcast)
• Metric used by routers not the same – loops
– No universal routing metric
– Policy drives routing decisions
51
NL: BGP
• BGP (Border Gateway Protocol): the de facto standard
• Path Vector protocol:
– similar to Distance Vector protocol
– each Border Gateway broadcast to neighbors (peers)
entire path (I.e, sequence of ASs) to destination
• E.g., Gateway X sends its path to dest. Z:
– Path (X,Z) = X,Y1,Y2,Y3,…,Z
– When AS gets route check if AS already in path
• If yes, reject route
• If no, add self and (possibly) advertise route further
– Allows for policy application (different metrics)
• Metrics are local - AS chooses path, protocol ensures no loops
Supports CIDR aggregation (BGP4)
Supports alternative routes
52
NL: Path Selection Criteria
• Path attributes + external (policy) information
• Examples:
– Hop count
– Policy considerations
• Preference for AS
• Presence or absence of certain AS
– Path origin
– Link dynamics
– Early-exit
• Hot-potato routing for transit packets
53
NL: Policy with BGP
• BGP provides capability for enforcing various
policies
• Policies are not part of BGP: they are provided to
BGP as configuration information
• BGP enforces policies by choosing paths from
multiple alternatives and controlling
advertisement to other AS’s
54
NL: Examples of BGP Policies
• A multi-homed AS refuses to act as transit
– Limit path advertisement
• A multi-homed AS can become transit for some
AS’s
– Only advertise paths to some AS’s
• An AS can favor or disfavor certain AS’s for
traffic transit from itself
55
NL: Interconnecting BGP Peers
• BGP uses TCP to connect peers
• Advantages:
– Simplifies BGP
– No need for periodic refresh - routes are valid until
withdrawn, or the connection is lost
• Note recent news on BGP TCP spoofing attack
– Incremental updates
• Disadvantages
– Congestion control on a routing protocol?
– Poor interaction during high load
56
NL: Internet inter-AS routing: BGP
• BGP messages exchanged using TCP.
• 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
57
NL: IPv4 summary
•
•
•
•
•
•
•
Security
Error detection
Delivery semantics
Quality-of-service
Fragmentation
Addressing
Routing
58
NL: IPv6
• Redefine functions of IP (version 4)
– Remove ancillary functionality
– Add missing, but essential functionality
– Recall, functions of IPv4
• What changes should be made in….
–
–
–
–
–
–
–
IP addressing
IP delivery semantics
IP quality of service
IP security
IP routing
IP fragmentation
IP error detection
59
NL: IPv6
• Initial motivation: 32-bit address space
completely allocated by 2008.
• Additional motivation:
– header format to help speed processing/forwarding
– header changes to facilitate QoS
– new “anycast” address: route to “best” of several
replicated servers
60
NL: IPv6 Header
0
4
Versi
on
12
Class
Payload Length
16
19
24
32
Flow Label
Next Header
Hop Limit
Source Address (128 bits)
Destination Address (128 bits)
61
NL: IPv6 Changes
• Scale – addresses are 128bit
– Header size?
• Simplification
– Removes infrequently used parts of header
– 40 byte fixed header vs. 20+ byte variable header
• IPv6 removes checksum
– Relies on upper layer protocols to provide integrity
– Reduces processing time at each hop
• IPv6 eliminates fragmentation
– Requires path MTU discovery
62
NL: IPv6 Changes
• TOS replaced with traffic class octet
– Support QoS via DiffServ
• FlowID field
– Help soft state systems, accelerate flow classification
– Maps well onto TCP connection or stream of UDP packets on
host-port pair
• Easy configuration
– Provides auto-configuration using hardware MAC address to
provide unique base
• Additional requirements
– Support for security
– Support for mobility
63
NL: IPv6 Changes
• Protocol field replaced by next header field
– Unify support for protocol demultiplexing as well as option
processing
• Option processing
– Options allowed, but only outside of header, indicated by
“Next Header” field
– Options header does not need to be processed by every router
• Large performance improvement
• Makes options practical/useful
• ICMPv6: new version of ICMP
– additional message types, e.g. “Packet Too Big”
– multicast group management functions
64
NL: Transition From IPv4 To IPv6
• Not all routers can be upgraded simultaneous
– no “flag days”
– How will the network operate with mixed IPv4 and
IPv6 routers?
• Two proposed approaches:
– Dual Stack: some routers with dual stack (v6, v4) can
“translate” between formats
– Tunneling: IPv6 carried as payload in an IPv4
datagram among IPv4 routers
65
NL: Dual Stack Approach
66
NL: Tunneling
IPv6 inside IPv4 where needed
67
NL: Network layer summary
• Network layer functions
• Specific network layers (IPv4, IPv6)
68