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SNU SCONE lab.
Problems of Addressing IP addressing scheme is too rigid
– One network ID for each organization
– Only three classes
Problems1. Large physical network (Large extended LAN)
2. Inefficient use of addresses• Need to allocate Class B address to a network with 255 hosts
– 255/65535 = 0.39% efficient
SNU SCONE lab.
Subnetting-1
Solution for large organizations
A class A (or B) network may have tens of thousand of hosts Problems?
One solution is to assign many class C addresses
Routing complexity increases
One Entry in
Forwarding Table
One
organization
One physical
network
One
organization
Many physical
networks
Many Entries in
Forwarding Table
Subnetting
Subnetting-2
Partition a large network into multiple small physical networks called subnet
Use a part of the host ID space for subnet identification– How do you know What part of
host ID is used for Subnet?
Subnet mask
Routing– Outside, route based on network ID (prefix) only
– Inside, route based on (network+subnet ID)
SNU SCONE lab. 4
SNU SCONE lab.
Subnet Example & Forwarding
ProcedureSubnet Mask: 255.255.255.128
Subnet Number: 128.96.34.0 (00100010 00000000)
Subnet Mask:
255.255.255.128
Subnet number:
128.96.34.128 (00100010 10000000)
Subnet Mask:
255.255.255.0
Subnet number:
128.96.33.0(00100001 00000000)
128.96.34.15 128.96.34.1
128.96.34.130
128.96.34.129 128.96.34.139
128.96.33.14 128.96.33.1
Router R0 Forwarding Table
SubnetNo SubnetMask NextHop
128.96.34.0 255.255.255.128 Interface 0
128.96.34.128 255.255.255.128 Interface 1
128.96.33.0 255.255.255.0 R1
R0
R1
IP Lookup procedure
Let D = Destination IP address
For each forwarding entry
D1 = SubnetMask & D
if D1 = SubnetNumber
Deliver to the NextHop
break
6
CIDR
Solution to efficient use of address
Allocate multiple (small) network IDs to an organization such that they can be aggregated into one prefix
CIDR(Classless Inter-Domain Routing), Supernetting– Ignore IP address class
– Variable network ID length
– Prefix: Network ID part of IP addresses
1010…..11 00
1010…..11 01
1010…..11 10
1010…..11 11
1010…..11
Prefix (22 bits)
Scenario:
A company with 900 hosts
10 bit host ID
24 bit
CIDR - Example
Network ID allocation & Aggregation– For a network with N hosts, host ID length should be at least n
where 2^n > N
• Use 32 -n bits for network ID
– Example:
• For an AS with 4,000 hosts, host ID part should be 12 bit long
– Network ID part is 20 bit long
– Share a common prefix (network ID part) of desired length
– Example
• 192.4.16.0-192.4.31.0 (11000000 00000100 0001xxxx xxxxxxxx)
• 16 class C addresses
SNU SCONE lab. 7
SubnetNumber SubnetMask NextHop
128.96.34.0 255.255.255.128 Interface 0
128.96.34.128 255.255.255.128 Interface 1
128.96.33.0 255.255.255.0 R2
SNU SCONE lab. 8
CIDR Notation
Notation
– IPAddress / length
• Length specifies the prefix used for network ID
• Similar to subnet mask
• 185.21.16.0/20 = 255.255.240.0
Forwarding table entry
– Use prefix length instead of subnet mask
SubnetNumber NextHop
128.96.34.0/25 Interface 0
128.96.34.128/25 Interface 1
128.96.33.0/24 R2
9
CIDR & Routing Route aggregation
Longest matching prefix
Destination NH
128.112.128.0/24 Int 0
128.112.128.0/21 Int 1
Forward a packet destines to 128.112.128.0?
Forward a packet destined to 128.112.129.0?
ISP2
11
Routing & Forwarding
Routing– Collect network information and determine shortest paths
– Path selection criteria
• Hop count, distance, reliability, QoS, …
– As a result, generate forwarding tables
Forwarding– Move packets according to forwarding table
SNU SCONE lab.
SNU SCONE lab. 12
Routing Scalability
Millions of networks in the Internet
Scalability problem
– Control packet overhead
– Processing overhead
Divide and conquer, Abstraction
Partition the Internet into pieces called AS
(Autonomous system) or RD(Routing Domain)
– Single authority unit over
• Address management & Routing inside the domain
– Examples
• ISP, Large University/company, …
AS ID (16 bit)
– Each AS has a unique ID
SNU SCONE lab. 13
Intra-/Inter-domain Routing Intradomain routing
– Routing within an AS where the owner has a complete control over the network operation
– Optimality > Reachability
– Collect all information & find shortest paths
– IGP (Interior Gateway Protocol)
– RIP, OSPF
Interdomain routing– Routing across AS boundaries
– AS would not disclose inside information
– Reachability > Optimality
– Exchange reachability info. between ASs
– EGP (Exterior Gateway Protocol)
– EGP, BGP-4
14
Graph Model Represent a network as a graph
– Node: network or router
– Link: network link
• Link cost
Find the shortest paths on the graph– Network conditions change dynamically
– Shortest path algorithms
Point-to-
point
Ethernet
FDDI
A
XY
Z B
x y z2 1 13
C=2
C=1
C=3
C=1
11
Ethernet
FDDI
P2P
Intradomain Routing Algorithm &
Protocol Routing algorithm = Shortest path algorithms
– Bellman-Ford algorithm
– Dijkstra algorithm
Routing protocol– Distributed realization of shortest path algorithms
• What information should be exchanged for distributeimplementation of shortest path algorithms?
– Application layer protocol that exchange
• Routing info.
• Network topology
• Network operating conditions
– Faults, congestion, estimated delay...
– RIP(Routing Information Protocol)
– OSPF(Open Shortest Path First)
SNU SCONE lab.
Shortest Path Algorithm
Graph G = (N,E)– Link (i, j) is incident on node i and j
• Associated cost,
– Path (i, j, k, l, ,m) is a series of links connecting two end nodes i and m
• Cost =
Shortest path algorithm– Find a path between two nodes with minimum cost
cij
lmkljkij cccc
SNU SCONE lab.
Bellman-Ford Algorithm
Let D(v) be the cost of current shortest path from node v to s
Algorithm
Step 1: D(s) = 0
D(v) = for all v
Step 2: D’(v) = min [D(u) +
u ∈ N(v)
If D’(v) = D(v) for all v , Stop
O.W. D(v) = D’(v) for all v
Repeat
cuv ]
sv
l
m
n
Distributed Implementation?
x
y
SNU SCONE lab.
DV (Distance-Vector) Algorithm
Based on distributed BF Algorithm
Each node sends to neighbor nodes its own optimal path costs as
– Distance vector
• Shortest path cost to each destination
Each node receives distance vector from all of its neighbor nodes and compute best routes
sv
l
m
n
1
5
2
x
y
19
BF - ExampleDistance to network
Router
4 8 12 16
A 0 1 1
B 1 0 4
C 1 4 0 3
D 3 0
Router
4 8 12 16
A ? ? ? ?
B ? ? ? ?
C ? ? ? ?
D ? ? ? ?
192.168.
0.48 12 16
A 0
B 0
C 0
D 0
SNU SCONE lab. 20
RIP
Neighbor routers exchange RIP request/response
messages that contain distance vector
When to send RIP messages?
– Periodic
– Triggered
Command Version 0
Family of Net1 0
Distance to Net1
Subnet Mask
Next hop
IP Address of Net1
Net2
Net3
...
Use UDP Port 520
How to limit the delivery
only to directly connected
routers?
Route Adaptation
(F)
(A)
(D)
(G)
(A)
(G)
Next Hop
Suppose F notices that link (F, G) is broken① F advertises to A that its cost to G is
② A receives from B, C and E with cost = 3, 2, 3,
respectively
③ A updates its route to G via C with cost 3
④ F receives advertisement from A and updates
the route via A with cost 4
SNU SCONE lab. 22
RIP Problem
Slow convergence– Count to infinity
A
D
C
B
10
1
11
1
Routing Table Updates
A B C D
d nh d nh d nh d nh
2 B 1 D 2 B 0 dd
2 B ∞ ur 2 B 0 dd
3 C 3 C 3 A 0 dd
4 C 4 C 4 A 0 dd
Before Break
23
Split Horizon & Poison Reverse Horizon
– Directions where to advertise distance-vector
Split horizon
– Do not advertise a route to an interface from where the best
trigger (next hop) arrives
Split horizon with Poison reverse
– Advertise a route with ∞ to an interface from where the best
trigger arrives
A
D
C
B
101
11
1
Routing Table Updates
A B C D
d nh d nh d nh d nh
2 B 1 D 2 B 0 dd
2 B ∞ ur 2 B 0 dd
Read: http://technet.microsoft.com/library/Cc940478
SNU SCONE lab.
Dijkstra Algorithm
Find shortest paths from node s
d
3
s
a b
c
e
1
2
22
1
13
55
Algorithm
Step 1: F = {s}
D(v) = 𝐶𝑠𝑣
Step 2: If F = N, Stop
O.W. Find u s.t. D(u) = min { D(x) }
x ∈ N-F
F = F + {u}
D(v) = min [D(v), D(u) + 𝐶𝑢𝑣], ∀ v ∈ N(u)
Repeat
SNU SCONE lab. 25
Link State Routing Protocol - 1 Problem of distance-vector routing protocol
– Large overhead
– Slow convergence
– Not scalable
• No hierarchy
Search for a new intra-domain routing protocol
– Starts in 1987
– Multiple paths between a source-destination pair
– Descriptive metric
– Hierarchy
Distributed database model
– Each router maintains complete network information
SNU SCONE lab. 26
Link State Routing Protocol - 2 Dijkstra (or any SP algorithms)
Procedure– Each router monitors the status of directly connected links
– Announce the link state information to all routers
• LSA (Link State Advertisement)
• Use flooding
– Collect LSAs into the local link state database and compute the shortest path tree rooted at the router
LSA contains– ID of the node that creates the LSA
– List of directly connected neighbors (routers and networks) and the cost(state) of each link
– Sequence number (SEQNO)
– LS Age
SNU SCONE lab.
LSA Flooding Reliable flooding
– Make sure LSA reaches to all routers
• While maintaining the efficiency of forwarding
– Use seqno to detect duplicate
Procedure– A router generates new LSA periodically
• Increment SEQNO
• Start SEQNO = 0 when reboot
– Flood to all links
– When a router receives an LSP
• Check the LSA is new one
• If new, store the LSA and after increment LSAge, flood to all interfaces except the one from which the LSP was received
• If not, ignore
SNU SCONE lab. 29
OSPF - Area
OSPF is very complex protocol
– Hierarchy
• A large AS/RD is partitioned
into several areas
– Load balancing
A large AS has thousands of routers
- Hierarchical structure
Area: a set of routers that exchange LSA
Area 0 : Backbone area
ABR(Area Border Router)
- Router that is both the member of
backbone area and non-backbone area
Use R4-R5 link?
Optimality vs. Scalability
SNU SCONE lab. 30
OSPF PDU – 1/2
Authentication
Version Type Message length
Checksum Authentication type
SourceAddr
AreaId
0 8 16 31
OSPF common header format
Incorrect routing may cause
large security problems
Make sure LSP is generated by
legitimate routers
Lowest IP address among the
IP addresses assigned to a router
Network
A
Network
B
OSPF PDU – 2/2
SNU INC lab. 31
(LSA) Link-State Advertisement
Network
A
Network
B
Type 1 LSA
Type 2 LSA
Link-state ID = Advertising router
Smallest IP address
Router ID
SNU SCONE lab. 32
Interdomain Routing
Interdomain routing problems
– Large size
– No centralized control or common metric
– Trust, policy
Interdomain routing protocols
– EGP (Exterior Gateway Protocol)
– BGP (Border Gateway Protocol)
SNU SCONE lab. 33
EGP & BGP EGP is designed for tree structured networks
Old Internet topology
There is only one ingress/egress
point to/from an AS
- Use the default route
Today’s multi-backbone Internet
- Loops
BGP
EGP
34
AS Types Stub AS
– AS that has a single connection to another AS
– Carry local traffic only
Multihomed AS– Connections to more than one AS
– Carry local traffic only
Transit AS– Connections to more than one AS
– Designed to provide transit services
35
BGP - Configuration
• Each AS has a BGP speaker
• Neighbor BGP speakers exchange reachability information (TCP)
• Determine paths to prefixes from the
collected reachability information
• Advertise the paths (reachability info) to
other AS
SNU SCONE lab.
36
BGP BGP speakers advertise
– Local networks
– (Transit AS only) Reachable networks with complete path
information
(128.96/16, AS2)
(128.96/16, AS1/AS2)
(128.96/16, AS3/AS1/AS2)
Why sending complete path info?
37
iBGP (interior BGP) Distribute reachability info to all routers within the AS
– Each router learns the best BG to route a packet to a particular prefix
Routers also runs a intradomain routing to find paths to BGs
SNU SCONE lab.
BG(Border GW)
SNU SCONE lab.
IPv6
IPv6 is a new IP that will replace IPv4
Urgency of new protocol
– Address space depletion
• IPv4 32 bit address can support only 4 billion nodes
• Expected to be full by year 20XX
The final day has been extended many times
Why?
SNU SCONE lab.
IPng
Ipng (IP next generation) WG
– IETF - 1991
– Developing a new protocol is once a lifetime opportunity
– Add functions that is/will be useful for the future Internet
Requirements
– Addressing Routing
– QoS(Quality of Service)
– Autoconfiguration
– Security
– Mobility
– Smooth transition
Select SIPP with minor modifications
– Called IPv6
– 128 bit address
SNU SCONE lab.
Address
Address types
Allocate addresses considering the ease of routing
Scalable Small routing table Aggregation (Hierarchy)
Hierarchy– Registry (Continent) > ISP (Backbone ISP > non-backbone ISP) >
Subscriber (AS) > Subnet > Host
– CIDR-like aggregation
• ISP obtains an address space and controls address allocation
• Ideally an ISP advertises only one prefix
Prefix Address Type Space
010 Provider based unicast 1/8
1111 1110 10 Link local 1/1024
1111 1110 11 Site local 1/1024
1111 1111 Multicast 1/256
SNU SCONE lab. 42
Addressing & Routing - 2
Geographic aggregation
– Hosts within a geographic region has the same prefix
– Continent level
– Registry ID
010 Registry ID ISP ID Subscriber ID Subnet ID Interface ID
3 m n o p 64
SNU SCONE lab. 43
IPv4 to IPv6 Transition & Address IPv4 to IPv6 transition is a difficult problem
Co-existence of IPv4 & IPv6
Approaches– Dual-stack
– Tunneling
Dual-stack– Process both IPv4 & IPv6 packets
Tunneling– Encapsulate IPv6 packet with IPv4 header
– Use IPv4-mapped IPv6 addresses for easy encapsulation
• 00..00 + IPv4-Address
V6
Sdr
V6
Rc
V4
NetworkV6 packet V6 packet
SNU SCONE lab. 44
Address Notation
Hexadecimal/2 byte separated by semicolons
– 47CD:1234:4422:AC02:0022:1234:A456:0124
Long contiguous 0 bits
– 47CD:0000:0000:0000:0000:0000:A456:0124
=> 47CD:: A456:0124
IPv4 part
– Dotted decimal
– ::FFFF:128.96.33.81
SNU SCONE lab.
IPv6 Packet Format - 1
Ves Class Flow Label
Payload length Next header Hop limit
SOURCE ADDRESS
DESTINATION ADDRESS
0 4 8 16 24 31
Hop-by-hop
Destination option
Routing header
Fragment header
Authentication header
ESP header
Next header
– Types of header appeared next to the IP header
• Ex: TCP: 6
Extension Header
– Options & Fragmentation info. are recorded in extension headers
– For fast packet processing at intermediate routers, extension
headers appear in a specific order
Fragmentation header
IPv6 Packet Format - 2
IPv6 header TCP header + Data
Next = TCP(6)
IPv6 header Routing header TCP header + Data
Next=routing(43) Next = TCP(6)
NextHeader Reserved Offset RES M
Ident
0 8 16 29 31
47
Autoconfiguration
Automatic configuration of IP address and other information
Two approaches– Stateful: DHCP
– Stateless: SLAAC(StateLess Address AutoConfiguration)
• Server-less autoconfiguration
How to create globally unique address?– Network prefix + Unique Interface ID
– Uniqueness of Interface ID is guaranteed at HW level
How to obtain the prefix?– Let the default router advertise the subnet prefix
– RS(Router Solicitation)
• Solicit the routing information
– RA(Router Advertisement)
• Inform prefix information and etc.
SNU SCONE lab.
Multicasting
Types of communications
– Unicast
– Broadcast
– Multicast
– Anycast
Importance of multicast
– Replicated data
– Entertainment
• IPTV, VOD, Game,..
Multicast requirements
– Efficiency
– Scalability
SNU SCONE lab. 50
Multicasting Methods
Multiple unicast (Simulcast)
– Unicast to each receiver
– Inefficient
• Sender processing
• Network traffic
– Management of (many) receivers is almost impossible
Router based multicast (IP level multicast)
– Routers replicate packets and forward to multiple links
S
R
R
Scalability
Router overhead
- Routing table
- Packet processing
SNU SCONE lab. 51
Multicast Models
SSM (Source Specific Multicast) vs ASM (Any Source
Multicast)
Centralized
– Each sender manages group members
• Hosts that wish to join/leave a multicast group should send
join/leave requests to the sender
– Difficult to implement IP-level multicast
Distributed
– No centralized member management function
– Hosts can join/leave multicast groups freely
• Host informs its router that it has joined a group
– Similar to broadcast & filtering
• TV, Radio
– Any host can send to a multicast group
IGMP (Internet Group Mgmt
Protocol) - 1 Two step multicast
– First distribute datagrams to multicast routers that have
multicast group members
– A multicast router handles multicasting within its subnet
IGMP
– A protocol to check the presence of group members within a
subnet
– Transmission of group membership query and response
between a multicast router and hosts
IGMP - 2
When a host joins a group
– Broadcast its membership
A multicast router periodically broadcasts group
membership queries
A host that is a member of a multicast group
responds to the poll
– After random delay between (0, 10) sec. Why?
Multicast
Router
Hosts
54
Multicast Routing Problem To do
– Install directives (like a forwarding Table) at each router
to duplicate (if necessary) and forward packets such that
all member routers receive the packets
Steiner tree problem
– Graph G = (V, E)
– R (receiver set) is a subset of V
– Find the best subtree of G that includes all R
– NP-Complete
– Compare to MST (Minimum Spanning Tree) problem
55
Multicast Tree Types Source based
– Use a shortest path tree (union of shortest paths) rooted on the
source
– Different multicast trees optimized to each source
Shared– Common tree used by all senders
SS
Mimic a Steiner Tree
How to build trees?
SNU SCONE lab. 56
Multicast Routing Protocols Source based tree protocols
– Per source and group (destination) overhead
– Good performance
– DVMRP, MOSPF, PIM-DM
Shared tree protocols
– Per group overhead
– Less efficient, traffic concentration
– CBT, PIM-SM
Source-based Shared
Tree OH High Low
Efficiency Good Poor
SNU SCONE lab.
DVMRP
Distance Vector Multicast Routing Protocol
RIP-dependent
– Uses RIP to exchange group membership information
Flood and prune protocol
– Broadcast to all networks through a spanning tree rooted at
the source
– Only routers w/ member accept packets
– Prune branches (subtrees) w/o members
Mechanisms
– RPB
– RPM
• Pruning & grafting
SNU SCONE lab. 58
RPB(Reverse Path Broadcast)
Dalal & Metcalfe(1978)
Broadcasting
– Avoid flooding loops
– Use shortest path from destination to source (reverse path)
Mechanism
– Flood (relay) a packet if the packet arrives on the shortest path
link to the source
– O.w. discard
– Compare to flooding used in OSPF LSA distribution
RPB achieves shortest path broadcast
S A
B
C
Problems of RPB
1. Broadcasts to subnets w/o group members
2. Multiple broadcasts to the same link
RPM (Reverse Path Multicast) delivers to routers with
group members only
Pruning
– Cut branches w/o members
– Start from leaf networks
– Non-member routers send prune upstream
• An upstream router prunes itself when all downstream routers send
prunes and sends prune upstream
Flood-and-pruning
– Repeat flood periodically to restore whole shortest path tree
RPM
SNU SCONE lab.
SNU SCONE lab. 61
Prune
S
R
R
Sender
Prune branches where no members and
branches not on shortest paths of other members
Example - Detailed
SNU SCONE lab. 62
h1
h5
h4
h3
h2
R2 knows that it is
responsible to h1
How?
Mark this fact and forward
multicast packet from D to
h1
How about Nx?
NxR1, R3 have the same cost to D
Decide a parent for h2
How?
Nz
NyDiff. btw Nx and (Ny, Nz)?
Ny is a leaf while Nx is not
How to know a network is leaf or not?
Single transmission
SNU SCONE lab.
MOSPF
Multicast extensions to OSPF
Extend LSA to report the groups active on a subnet
– Group-Membership-LSA
Source/destination routing
– Source-based shortest path trees
SNU SCONE lab. 65
PIM(Protocol Indep. Multicast)
Motivation
– Independence from unicast routing
– Group members may be sparsely/densely populated
– Select shared/source-based trees flexibly
– Also, consider traffic intensity
SM (Sparse Mode)Simplicity is important
Shared tree & Source-specific tree
DM (Dense Mode)Efficiency is important
Source based tree
Similar to DVMRP
PIM-SM
SNU SCONE lab. 66
Start w/
Shared Tree
Convert to
Source
specific tree
RP(Rendezvous Point) of each group
is determined in advance
GA In Sndr Out
G RP-R2 * R2-R4
* R2-R5
RP sends JOIN message to the sender
Create sender-specific forwarding state
(S,G) state
No encapsulation
But, shared tree
inefficiency
GA In Sndr Out
G R1-R3 S R3-RP
Sender-specific state
R
R
R
R
R
R
R
R
SNU SCONE lab. 67
PIM-SM Transmission
DR (Designated Router)
Overhead
How to decrease the overhead?
Tunneling
REGISTER
SNU SCONE lab. 68
Interdomain Multicast
DVMRP, MOSPF are for intradomain multicast
Suppose to use PIM for interdomain multicast– Location of RP
– Triangle routing
How to build interdomain multicast?
Interdomain– Source-specific tree
Intradomain– Each domain operates PIM-SM with its own RPs
RPR
S
R
SNU SCONE lab. 69
MSDP (Multicast Source Discovery)
RPs are connected to MSDP
peers in foreign domains
Informs active senders to MSDP
peers
Foreign RPs send JOIN
messages to active senders to
form a sender-specific tree
across domain boundary
SNU SCONE lab. 70
PIM-SSM
Source-specific multicast for one-to-many applications
Channel
– (S, G) combination
Mechanism
– A receiver report membership (channel) to a local router
– The local router sends a JOIN message to the sender
• Bypass shared tree construction
– Forms sender-specific multicast tree
Can be used for interdomain milticast
SNU SCONE lab. 71
BIDIR-PIM (Bidirectional)
For many-to-many
applications within a domain
– Conference
Forward packets regardless
of incoming interface
– Note PIM-SM forwards a packet
only when it is arrived from the
upstream (i.e. from the RP)
Host Mobility Support The Internet uses network based routing for scalability
– Assume hosts do not change locations (attachments)
What happens if hosts roam changing physical networks?– IP addresses should be changed
Root Cause of the problem
IP address is both Identifier & Locator
Separate ID & Locator roles
CN
MN
(Mobil Node)
Invariant IP Address
Suppose we change the IP addresses of an MN– To communicate with the MN, CNs should know the new address
– Can it be done?
The Internet was designed w/ an assumption that IP
address is fixed
– TCP connection (Flow) is defined by
• Source address & port number
• Destination address & port number
How to support mobility while not violating the Internet
semantics?
– And your solution should be scalable, simple, etc
SNU SCONE lab. 74
Architecture & Basic Mechanism
MN (Mobile Node)
CN (Correspondent Node)
HA (Home Agent)FA (Foreign Agent)
HN (Home Network)VN (Visited Network)
MN
CN
TunnelHA
FA
VNHN
● Preparation
1. MN obtains a new address (called CoA (care-of address) at the VN
2. MN informs the care-of address to the HA using BU (Binding Update)
Two types of CoA
- Co-located CoA
- FA CoA
Tunneling & Encapsulation
MN
CN
TunnelHA
FA
VNHN
HoA Data
CA HoA DataS? D? HoA (Home Address)
CoA (Care-of Address)
CA(CN’s Address)
● CN MN
1. CN transparently sends a datagram to the MN w/ the original IP address (HoA)
2. The datagram arrives at HN(Home Network) & ARP request (may) will be issued
3. HA intercepts packets to the MN (How?)
4. HA relays packets to the VN for the MN
● MN CN
Destination address? Source address?
Any problems?
CA HoA Data
CA
Route Optimization
Problem - Triangle routing
– Packets from CN to MN are relayed through HA
Route optimization
– Send packets directly to the MN
– MN sends BU to the CN
– CN maintains “Binding cache “& sends datagrams to the
MN directly
Is encapsulation still needed?
Probably Yes!! Why?
CN
HA FA
MN
CA CoA DATA
CA HoA DATA
SNU SCONE lab.
Cache Consistency
MN moves to a new location
– Cache consistency problem
• CNs may have old care-of-address
HA FA1
CN
FA2
MN
Registration
Binding
update
Binding
Ack
In case of MN’s registration to a new FA
- Send BU to the previous FA
- Old FA also maintains binding cache and replies with “Binding Ack”
Send warning message to CNs