Subnet & Supernet

Chong-kwon Kim

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

Routing

Chong-kwon Kim

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. 28

Flooding: Example

X

C

A

B D

X

C

A

B D

X

C

A

B

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)

IPv6

Chong-kwon Kim

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.

Multicast

Chong-kwon Kim

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

59

Example

S

R

R

Sender

S

R

R

Sender

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

Example - Detailed

SNU SCONE lab. 63

h1

h5

h2

Nx

Nz

Ny

No memberNo member

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)

MIP (Mobile IP)

Chong-kwon Kim

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