EPL476 Mobile Networks

Mobile Network Protocols

Instructor: Dr. Vasos Vassiliou

Slides adapted from Prof. Dr.-Ing. Jochen H. Schiller and W. Stallings

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MOBILE NETWORK LAYER

Mobile IP

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Mobile IP (I) Mobile IP adds mobility support to the Internet network

layer protocol IP. The Internet started at a time when no-one had a concept of

mobile computers.• The Internet of today lacks mechanisms for the support of users

traveling through the world.– IP is the common base for thousands of applications and runs over dozens of

different networks; this is the reason for supporting mobility at the IP layer.

Motivation for Mobile IP: Routing

• based on IP destination address, network prefix determines physical subnet

• Change of physical subnet implies change of IP address to have a topological correct address (standard IP) or needs special entries in the routing tables

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Mobile IP (II)

Create specific routes to end-systems – mobile nodes?

• change of all routing table entries to forward packets to the right destination

• does not scale with the number of mobile hosts and frequent changes in the location

Changing the IP address?• adjust the host IP address depending on the current

location• almost impossible to find a mobile host, DNS has not been

built for frequent updates• TCP connection break

5

Mobile IP (III)

Requirements to Mobile IP: Transparency

• mobile end-systems keep their IP address• continuation of communication after interruption of link

possible• point of connection to the fixed network can be changed

Compatibility• support of the same layer 2 protocols as IP does• no changes to current end-systems and routers required• Mobile end-systems can communicate with fixed systems

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Mobile IP (IV)

Security• authentication of all registration messages

Efficiency and scalability• only little additional messages to the mobile system

required (connection typically via a low bandwidth radio link)

• world-wide support of a large number of mobile systems in the whole Internet

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Real-life Solution

Take up the analogy of you moving from one apartment to another. What do you do? Leave a forwarding address with your old

post-office The old post-office forwards mail to your

new post-office, which then delivers it to you

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Mobile IP - Definition

“Mobile IP (MIP) is a modification to IP that allows nodes to continue to receive datagrams no matter where they happen to be attached to the Internet”

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Mobile IP (V)

Terminology: Mobile Node (MN)

• system (node) that can change the point of connection to the network without changing its IP address

Home Agent (HA)• system in the home network of the MN, typically a router• registers the location of the MN, tunnels IP datagrams to the COA

Foreign Agent (FA)• system in the current foreign network of the MN, typically a

router• forwards the tunneled datagrams to the MN, typically also the

default router of the MN

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Mobile IP (VI)

Care-of Address (COA)• address of the current tunnel end-point for the MN (at FA

or MN)• actual location of the MN from an IP point of view• can be chosen, e.g., via DHCP

Correspondent Node (CN)• communication partner

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Mobile IP in detail …

Combination of 3 separable mechanisms: Discovering the care-of address Registering the care-of address Tunneling to the care-of address

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CN

2. HA Discovery Request

3. HA Discovery Reply

4. HA Registration through FA

5. HA Registration Ack.

1. CoA Discovery

MN HA

1

2

3

-- MN is Registered with HA --

4

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-- CoA and HA Discovery --

-- Registration Procedure --

-- CN starts communication with MN --6. Data Packet

7. IP-in-IP Encapsulation

8. Tunneled Data

-- Signals 6-10a as above --

8 77

6a. Data Packet

-- MN starts communication with CN --

8a Detunnelled Data

9. Binding Update

6a6a

-- Discovery and Registration as above --

FA

8a

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1010. IP-in-IP tunneling

99

10a 10a. Detunnelled Data

CN

2. HA Discovery Request

3. HA Discovery Reply

4. HA Registration BU

5. HA Registration BU Ack.

1. CoA Discovery

MN HA

1

2

3

-- MN is Registered with HA --

4

55

-- CoA and HA Discovery --

-- Registration Procedure --

-- CN starts communication with MN --

6. Data Packet

7. IP-in-IP Encapsulation

8. Tunneled Data

-- Signals 6-10 as above --

8

77

6a. Data Packet

-- MN starts communication with CN --

9. Binding Update

6a6a

-- Discovery and Registration as above --

FA

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1010. Binding Ack

99

MIPv4 MIPv6

Mobile IP in detail

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Discovering the care-of address Discovery process built on top of an existing

standard protocol: router advertisements Router advertisements extended to carry

available care-of addresses called: agent advertisements

Foreign agents (and home agents) send agent advertisements periodically

A mobile host can choose not to wait for an advertisement, and issue a solicitation message

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Agent advertisements

Foreign agents send advertisements to advertise available care-of addresses

Home agents send advertisements to make themselves known

Mobile hosts can issue agent solicitations to actively seek information

If mobile host has not heard from a foreign agent its current care-of address belongs to, it seeks for another care-of address

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Registering the Care-of Address Once mobile host receives care-of address, it

registers it with the home agent A registration request is first sent to the home

agent (through the foreign agent) Home agent then approves the request and

sends a registration reply back to the mobile host

Security?

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Registration Illustration

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Home agent discovery

If the mobile host is unable to communicate with the home agent, a home agent discovery message is used

The message is sent as a broadcast to the home agents in the home network

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Tunneling to the Care-of address When home agent receives packets addressed

to mobile host, it forwards packets to the care-of address

How does it forward it? - encapsulation The default encapsulation mechanism that

must be supported by all mobility agents using mobile IP is IP-within-IP

Using IP-within-IP, home agent inserts a new IP header in front of the IP header of any datagram

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Tunneling (contd.)

Destination address set to the care-of address

Source address set to the home agent’s address

After stripping out the first header, IP processes the packet again

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Tunneling Illustration

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(current physical network for the MN)

home network

(physical home networkfor the MN)

Mobile IP (VII)

Example network

Internet

router

HAMN

router

FA foreign network

routerend-system

CN

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Mobile IP (VIII)

Data transfer to the mobile system

Internethome network

foreignnetwork

FA

HA

MN

receiver

1

2

3

sender

CN

1. Sender sends to the IP address of MN, HA intercepts packet2. HA tunnels packet to COA, here FA, by encapsulation3. FA forwards the packet to the MN

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foreignnetwork

home network

Mobile IP (IX)

Data transfer from the mobile system

Internet

HA

MN

sender

receiver

CN

1. Sender sends to the IP address of the receiver as usual, FA works as default router

FA

1

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Mobile IP (XIII)

Optimization of packet forwarding: Triangular routing

• sender sends all packets via HA to MN• higher latency and network load

Solutions – optimization• HA informs a sender about the location of MN • sender learns the current location of MN• direct tunneling to this location• big security problems!

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Mobile IP (XIV)

Change of FA• Packets on-the-fly during the change can be lost• new FA informs old FA to avoid packet loss, old FA

forwards remaining packets to new FA• this information also enables the old FA to release

resources for the MN

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Mobile IP (XV)

Change of the foreign agent with the optimized mobile IP

CN HA FAold FAnew MN

t

requestupdate

ACKdata data

MN changeslocationregistration

updateACKdata

data datawarning

update

ACKdata

data

registration

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Mobile IP (XVI) Reverse tunneling:

Internet

receiver

FA

HA

MN

home network

foreignnetwork

sender

3

2

1

1. MN sends to FA2. FA tunnels packets to HA by encapsulation3. HA forwards the packet to the receiver (standard case)

CN

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Mobile IP (XVII)

Mobile IP with reverse tunneling Router accept often only “topological correct“ addresses

(firewall!)• a packet from the MN encapsulated by the FA is now topological

correct• furthermore multicast and TTL problems solved (TTL in the

home network correct, but MN is to far away from the receiver) Reverse tunneling does not solve

• problems with firewalls, the reverse tunnel can be abused to circumvent security mechanisms (tunnel hijacking)

• optimization of data paths, i.e. packets will be forwarded through the tunnel via the HA to a sender (double triangular routing)

The standard is backwards compatible• the extensions can be implemented easily and cooperate with

current implementations without these extensions • Agent Advertisements can carry requests for reverse tunneling

29[modified from Ericsson Tech. Rep. 11/0362-FCB, Dec 2000 ]

Mobile IP in detail

type = 16

length = 6 + 4 * #COAs

R: registration required

B: busy, no more registrations

H: home agent

F: foreign agent

M: minimal encapsulation

G: GRE encapsulation

r: =0, ignored (former Van Jacobson compression)

T: FA supports reverse tunneling

reserved: =0, ignored

Agent advertisement

preference level 1router address 1#addressestype

addr. size lifetimechecksum

COA 1COA 2

type = 16 sequence numberlength

0 7 8 15 16 312423code

preference level 2router address 2

. . .

registration lifetime

. . .

R B H F M G r reservedT

Registration

t

MN HAregistrationrequest

registration

reply

t

MN FA HAregistrationrequestregistrationrequest

registration

reply

registration

reply

Mobile IP registration request

home agenthome addresstype = 1 lifetime0 7 8 15 16 312423

T x

identification

COA

extensions . . .

S B DMGr

S: simultaneous bindings

B: broadcast datagrams

D: decapsulation by MN

M mininal encapsulation

G: GRE encapsulation

r: =0, ignored

T: reverse tunneling requested

x: =0, ignored

Mobile IP registration reply

home agenthome addresstype = 3 lifetime0 7 8 15 16 31

code

identification

extensions . . . Example codes:

registration successful

0 registration accepted

1 registration accepted, but simultaneous mobility bindings unsupported

registration denied by FA

65 administratively prohibited

66 insufficient resources

67 mobile node failed authentication

68 home agent failed authentication

69 requested Lifetime too long

registration denied by HA

129 administratively prohibited

131 mobile node failed authentication

133 registration Identification mismatch

135 too many simultaneous mobility bindings

Encapsulation

original IP header original data

new datanew IP header

outer header inner header original data

Encapsulation I Encapsulation of one packet into another as payload

e.g. IPv6 in IPv4 (6Bone), Multicast in Unicast (Mbone) here: e.g. IP-in-IP-encapsulation, minimal encapsulation or GRE (Generic

Record Encapsulation) IP-in-IP-encapsulation (mandatory, RFC 2003)

tunnel between HA and COA

Care-of address COAIP address of HATTLIP identification

IP-in-IP IP checksumflags fragment offsetlengthDS (TOS)ver. IHL

IP address of MNIP address of CNTTLIP identification

lay. 4 prot. IP checksumflags fragment offsetlengthDS (TOS)ver. IHL

TCP/UDP/ ... payload

Encapsulation II Minimal encapsulation (optional)

avoids repetition of identical fields e.g. TTL, IHL, version, DS (RFC 2474, old: TOS) only applicable for non fragmented packets, no space left for

fragment identification

care-of address COAIP address of HATTLIP identification

min. encap. IP checksumflags fragment offsetlengthDS (TOS)ver. IHL

IP address of MNoriginal sender IP address (if S=1)

Slay. 4 protoc. IP checksum

TCP/UDP/ ... payload

reserved

Generic Routing Encapsulation original

headeroriginal data

new datanew header

outer headerGRE header

original dataoriginalheader

Care-of address COAIP address of HATTLIP identification

GRE IP checksumflags fragment offsetlengthDS (TOS)ver. IHL

IP address of MNIP address of CNTTLIP identification

lay. 4 prot. IP checksumflags fragment offsetlengthDS (TOS)ver. IHL

TCP/UDP/ ... payload

routing (optional)sequence number (optional)key (optional)

offset (optional)checksum (optional)protocolrec. rsv. ver.CRK S s

RFC 1701

RFC 2784 (updated by 2890)

reserved1 (=0)checksum (optional)protocolreserved0 ver.C

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Route Optimizations

Enable direct notification of the corresponding host

Direct tunneling from the corresponding host to the mobile host

Binding cache maintained at corresponding host

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Route optimizations (contd.)

4 types of messages Binding update Binding request Binding warning Binding acknowledge

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Binding Update

When a home agent receives a packet to be tunneled to a mobile host, it sends a binding update message to the corresponding host

When a home agent receives a binding request message, it replies with a binding update message

Also used in the the smooth-handoffs optimization

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Binding Update (Contd.)

Corresponding host caches binding and uses it for tunneling subsequent packets

Lifetime of binding? Corresponding host that perceives a near-

expiry can choose to ask for a binding confirmation using the binding request message

Home agent can choose to ask for an acknowledgement to which a corresponding host has to reply with a binding ack message

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Binding warning

When a foreign agent receives a tunneled message, but sees no visitor entry for the mobile host, it generates a binding warning message to the appropriate home agent

When a home agent receives a warning, it issues an update message to the corresponding host

What if the foreign agent does not have the home agent address (why?) ?

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Binding Update and Warning

Home Agent

Foreign AgentCorresponding Host

Mobile Host

BU BW

BW

BRBA

Optimization of packet forwarding Problem: Triangular Routing

sender sends all packets via HA to MN higher latency and network load

“Solutions” sender learns the current location of MN direct tunneling to this location HA informs a sender about the location of MN big security problems!

Change of FA packets on-the-fly during the change can be lost new FA informs old FA to avoid packet loss, old FA now

forwards remaining packets to new FA this information also enables the old FA to release

resources for the MN

Change of foreign agent CN HA FAold FAnew MN

MN changeslocation

t

Data Data DataUpdate

ACK

Data Data

RegistrationUpdate

ACKData

Data DataWarning

Request

Update

ACK

DataData

Reverse tunneling (RFC 3024, was: 2344)

Internet

receiver

FA

HA

MN

home network

foreignnetwork

sender

3

2

1

1. MN sends to FA

2. FA tunnels packets to HA

by encapsulation

3. HA forwards the packet to the

receiver (standard case)

CN

Mobile IP with reverse tunneling Router accept often only “topological correct“ addresses

(firewall!) a packet from the MN encapsulated by the FA is now topological

correct furthermore multicast and TTL problems solved (TTL in the home

network correct, but MN is to far away from the receiver) Reverse tunneling does not solve

problems with firewalls, the reverse tunnel can be abused to circumvent security mechanisms (tunnel hijacking)

optimization of data paths, i.e. packets will be forwarded through the tunnel via the HA to a sender (double triangular routing)

The standard is backwards compatible the extensions can be implemented easily and cooperate with

current implementations without these extensions Agent Advertisements can carry requests for reverse tunneling

48

Mobile IP and IPv6 Mobile IP was developed for IPv4, but IPv6 simplifies the

protocols security is integrated and not an add-on, authentication of

registration is included COA can be assigned via auto-configuration (DHCPv6 is one

candidate), every node has address autoconfiguration no need for a separate FA, all routers perform router

advertisement which can be used instead of the special agent advertisement; addresses are always co-located

MN can signal a sender directly the COA, sending via HA not needed in this case (automatic path optimization)

„soft“ hand-over, i.e. without packet loss, between two subnets is supported

• MN sends the new COA to its old router• the old router encapsulates all incoming packets for the MN and

forwards them to the new COA• authentication is always granted

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Problems with mobile IP Security

authentication with FA problematic, for the FA typically belongs to another organization

no protocol for key management and key distribution has been standardized in the Internet

patent and export restrictions Firewalls

typically mobile IP cannot be used together with firewalls, special set-ups are needed (such as reverse tunneling)

QoS many new reservations in case of RSVP tunneling makes it hard to give a flow of packets a special

treatment needed for the QoS Security, firewalls, QoS etc. are topics of current research

and discussions!

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Security in Mobile IP Security requirements (Security Architecture for the Internet

Protocol, RFC 1825) Integrity

any changes to data between sender and receiver can be detected by the receiver

Authenticationsender address is really the address of the sender and all data received is really data sent by this sender

Confidentialityonly sender and receiver can read the data

Non-Repudiationsender cannot deny sending of data

Traffic Analysiscreation of traffic and user profiles should not be possible

Replay Protectionreceivers can detect replay of messages

not encrypted encrypted

IP security architecture I Two or more partners have to negotiate security

mechanisms to setup a security association typically, all partners choose the same parameters and

mechanisms Two headers have been defined for securing IP packets:

Authentication-Header• guarantees integrity and authenticity of IP packets• if asymmetric encryption schemes are used, non-repudiation

can also be guaranteed

Encapsulation Security Payload• protects confidentiality between communication partners

Authentification-HeaderIP-Header UDP/TCP-Paketauthentication headerIP header UDP/TCP data

ESP headerIP header encrypted data

Mobile Security Association for registrations parameters for the mobile host (MH), home agent (HA),

and foreign agent (FA) Extensions of the IP security architecture

extended authentication of registration

prevention of replays of registrations• time stamps: 32 bit time stamps + 32 bit random number• nonces: 32 bit random number (MH) + 32 bit random number

(HA)

registration reply

registration requestregistration request

IP security architecture II

MH FA HAregistration reply

MH-HA authenticationMH-FA authentication FA-HA authentication

Key distribution

Home agent distributes session keys

foreign agent has a security association with the home agent

mobile host registers a new binding at the home agent home agent answers with a new session key for foreign

agent and mobile node

FA MH

HA

response:

EHA-FA {session key}

EHA-MH {session key}

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Recap

Host mobility and Internet addresses Post-office analogy Home agent, foreign agent, care-of address,

home address Registration and Tunneling Mobile IP problems Mobile IP Optimizations Other options