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Mobility Management

Motivation

Approaches to mobility

management

Layer 2 mobility

Mobile IP (layer 3 mobility)

Data transfer

Encapsulation

IPv6

Problems

DHCP

Mobile Communication Networks 2 Andreas Mitschele-Thiel, Florian Evers 24-Jan-13

Motivation

Routing

forwarding is based on some destination address (a locator)

change of location (due to mobility) requires change of destination address

or needs an update of routing tables

Ideas:

Specific routes to end systems (per-host forwarding)

Multicast

Modification of the destination address

Tunneling


Motivation

BS

BS

BS

BS

Source

Internet

Specific routes to end systems (per-host forwarding)

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

=> distribution of routing information for every mobile everywhere

=> does not scale to a large network

=> security problems (routing table updates)


Motivation

Multicast

Building of a multicast tree

=> security problem

=> Overhead

BS

BS

BS

BS

Source

Internet HA


Motivation

BS

BS

BS

BS

Source

Internet

Modification of the destination address

adjust the host address depending on the current location

=> problems to find a mobile host without a constant address

=> problems with application due to change of address

=> security problem HA


Motivation

BS

BS

BS

BS

Source

Internet

Tunneling

Separation of a terminal/user identificator from a topological locator

=> security problem (location update at home agent)

HA


Motivation

Important tasks of mobility management:

Find and address a mobile away from home

Support ``continuous´´ communication after change of location

Security: avoid misuse of mechanism

Privacy: hide location from others

Important criteria to compare mobility protocols:

Handover (HO) performance:

delay to update the route

packet loss due to handover

Protocol overhead: consumption of network resources

Scalability: protocol overhead in large networks with large numbers of

mobile nodes

Robustness: adaptability to different network conditions and failures

Ease of deployment: simplicity, suitability to different network scenarios


Approaches to Mobility (Which Layer Handles Mobility?)

Mobility may be supported at different layers:

Layer 1 (radio link addition or deletion – radio mobility)

UMTS/GSM: HO between cells supported by a single base station

Layer 2 (switching: mobility is hidden from layer 3 – micro mobility)

UMTS/GSM: HO in core network (SGSN) or in radio access network (RNC)

WLAN: change between access points belonging to same subnet

Layer 3 (routing: mobility beyond a single subnet – macro mobility)

Goal, No changes of upper layers protocols, change of network architecture is

allowed

Mobile IP and derivatives


Approaches to Mobility (Which Layer Handles Mobility?)

Layer 4 (transport)

Goal, keep the Internet infrastructure unchanged by allowing the end hosts to

take care of mobility

UMTS/GPRS: routing based on traffic flow template (QoS-specific)

considering port IDs, etc. (GTP-U)

Layer 5 (session)

Change of mapping of identity/number to destination address

Layer 7 (application)

No changes in the current networks

Extending IP telephony infrastructure to fulfil the mobility requirements

DNS: change of mapping of name (e.g. URL) to IP address

Hybrid Layers Mobility

Optimization of a certain layer mobility using information from other layers or

Integrated solution Instead of hybrid solution


Layer 2 Mobility (Micro Mobility)

Mobility is completely hidden from the IP layer

Mobility is handled by layer 2 either by

per-host forwarding: update of address tables in switches

tunneling: use of second address as locator

Examples:

802.11 uses ARP updates (per-host forwarding)

change of mapping of MAC address to output port

UMTS/GPRS applies

per-host forwarding between core network elements

tunneling to pass intermediate nodes (IP routers) between

network elements


Layer 2 Mobility in IEEE 802.11

4 phases

Recognizing the lost in the connection

Search and detection of new adequate AP

Re-/Authentication with the new discovered AP

Re-/Association with the new discovered AP

Recognizing the lost in the connection through the weakness of the

received signal or on the failed frame transmissions

Search and detection of new adequate AP through scanning the

medium, passive and active scanning are the standard methods


Layer 2 Mobility in 802.11

large variation for the same hardware

with same configuration

Scanning is the main factor in layer2

latency, about 90%.

Speeding the scanning, periodic

scanning, selective scanning

STA APs

Association phase

Authentication phase

Scanning phase

New AP


Layer 2 Mobility in UMTS/GPRS

L1

RLC

PDCP

MAC

E.g., IP,

PPP

Application

L1

RLC

PDCP

MAC

ATM

UDP/IP

GTP-U

AAL5

Relay

L1

UDP/IP

L2

GTP-U

E.g., IP,

PPP

3G-SGSNUTRANMS

Iu-PSUu Gn Gi

3G-GGSN

ATM

UDP/IP

GTP-U

AAL5

L1

UDP/IP

GTP-U

L2

Relay

Terminal IP to location IP mapping

(termination of IP tunnel) Per host routing Per-host routing

Tunneling via intermediate IP

routers


IP-based Mobility

IP Routing

forwarding is based on IP destination address; network prefix (e.g. 129.13.42)

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

Basic Mechanisms:

Specific routes to end-system: per-host forwarding

distribution of routing information to every router/switch

change of multiple routing table entries upon terminal movement

does not scale well with the number of routers and mobile hosts

Separation of terminal identity from location: tunneling

terminal/user identifier and topological location address

high latency for updates

Multicast

Modification of destination address depending on current location

almost impossible to find a mobile system

DNS updates take to long time

TCP connections break


Mobile IP (Layer 3 – Macro Mobility)

Requirements for Mobile IP:

Transparency

mobile end-systems keep their IP address

continuation of communication after interruption of link

point of connection to the fixed network can be changed

Compatibility

support of the same layer 2 protocols as IP

no changes to current end-systems and routers required

mobile end-systems can communicate with fixed systems

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


Mobile IP Basics: Example Network

mobile end-system Internet

router

router

router

end-system

FA

HA

MN

home network

foreign

network

(physical home network

for the MN)

(current physical network

for the MN)

9.4.1

CN


Mobile IP 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 for the MN

Care-of Address (COA)

address of the current tunnel end-point for the MN (at FA or MN)

current location of the MN from an IP point of view

can be chosen, e.g., via DHCP (Co-located COA)

Correspondent Node (CN)

communication partner


Basics: Data transfer to the mobile node

Internet

sender

FA

HA

MN

home network

foreign

network

receiver

1

2

3

1. Sender sends to the IP address of MN,

HA intercepts packet (proxy ARP)

2. HA tunnels packet to COA, here FA,

by encapsulation

3. FA forwards the packet

to the MN

CN


Basics: Data transfer from the mobile node

Internet

receiver

FA

HA

MN

home network

foreign

network

sender

1

1. Sender sends to the IP address

of the receiver as usual,

FA works as default router CN


Agent Discovery and Registration (IPv4)

Here the care-of address denotes the address of the FA

the MN could also get it directly via DHCP (co-located care-of address)

The binding update is a remote redirect and therefore needs authentication

After registration the HA tunnels data for the MN to the care-of address

IPv4

Foreign network

Home Agent

Foreign Agent advertises service

1. Foreign Agent, Care-of address

Mobile Node

2. MN sends Registration Request 3. FA relays Binding Update to HA

5. HA accepts binding or denies

6. FA relays status to MN

4. HA maintains the association between home address and current care-of address and registration lifetime (binding)

Home network


Agent Discovery and Registration

FA

FA

FA

FA

Source

Internet HA

10.10.0.0

9.9.0.0

Home address:10.10.0.10

CoA:

1- FA-CoA: 9.9.0.0 or

2- Co-located CoA: 9.9.x.x

Destination is: 10.10.0.10



FA

FA

FA

FA

Source

Internet HA

10.10.0.0

9.9.0.0

Home address:10.10.0.10

CoA:

1- FA-CoA: 9.9.0.0 or

2- Co-located CoA: 9.9.0.2

De-tunneling by MN



Agent Advertisement

HA and FA periodically send advertisement messages into their physical

subnets

MN listens to these messages and detects, if it is in the home or a foreign

network

MN reads a COA from the FA advertisement messages

Note: agent advertisement may be solicited by MN (agent solicitation msg)

Registration (always limited lifetime!)

MN signals COA to the HA via the FA, HA acknowledges via FA to MN

these actions have to be secured by authentication

Advertisement (ICMP extensions to RFC 1256)

HA advertises the IP address of the MN (as for fixed systems), i.e.

standard routing information

routers adjust their entries; these are stable for a longer time (HA

responsible for a MN over a longer period of time)

packets to the MN are sent to the HA, independent of changes in COA/FA


Tunneling

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 COA IP address of HA

TTL IP identification

IP-in-IP IP checksum flags fragment offset

length TOS ver. IHL

IP address of MN IP address of CN


lay. 4 prot. IP checksum flags fragment offset

length TOS ver. IHL

TCP/UDP/ ... payload

MIP header

IP packet


Tunneling

Minimal encapsulation (optional)

avoids repetition of identical fields

e.g. TTL, IHL, version, TOS

only applicable for unfragmented packets, no space left for fragment

identification

care-of address COA IP address of HA


min. encap. IP checksum flags fragment offset

length TOS ver. IHL

IP address of MN original sender IP address (if S=1)

S lay. 4 protoc. IP checksum

TCP/UDP/ ... payload

reserved

MIP header

minimized

IP packet


Optimization of packet forwarding

Triangular Routing

sender sends all packets via HA to MN

=> higher latency and network load

Ideas for Solutions

sender learns the current location of MN

direct tunneling to this location

HA informs a sender about the location of MN

security problems with binding updates

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


Tunneling and Route Optimization (IPv4)

The home agent can either use IP-within-IP or minimal encapsulation to reduce the header overhead

Route optimization can be done if the HA sends a Binding Update to the CN

=> subsequent packets can be tunneled directly from the CN to the FA

In the reverse direction normal standard IP routing mechanisms are used to deliver IP datagrams from the MN

Problems if the MN moves to another FA!

Home network

Foreign network

Home Agent Foreign Agent

Mobile Node

3. FA strips off the tunnel header and relays the rest to the MN

1. CN sends IP packet to home address of MN. Initially the CN only knows the home address of the MN

Correspondent Node

2. HA encapsulates the IP packet into a new IP packet by adding a tunneling header with the care-of address as destination. Tunnel source IP address is the HA address

4. HA can send a binding update to CN

5. The CN can tunnel IP packets directly to the FA


After having moved to the new FA, the MN can also communicate its new care-of address to the previous FA

Note that most of the Binding Update messages are not emitted by the MN, thus they are not going over the wireless link

Problem if FA 1 does not know the new care-of address of the mobile node:

FA1 must re-route the traffic to the HA, which again handles it via a new tunnel to FA2

Foreign Agent 1 Mobile Node

Correspondent

Node 4. The FA 1 tunnels the IP

packets to the MN’s new

location (FA 2)

3. CN attempts to

reach the MN

using the obsolete

care-of address

Foreign Agent 2

1. MN moves to a new

subnet

5. FA 2

relays to

the MN

Home Agent 6. FA 1 sends the HA a Binding

Warning and asks the HA to

send the CN a Binding

Update

8. Now the CN can again

tunnel more directly to the

MN

7. HA sends a Binding

Update to the CN

Change of foreign agent (IPv4)

2. MN communicates its new

care-of address (of FA 2) to

the previous FA


Change of foreign agent

CN HA FAold FAnew MN

MN changes

location

t

Data Data Data Update

ACK

Data Data

Registration Update

ACK Data

Data Data Warning

Request

Update

ACK

Data Data


Reverse tunneling (RFC 3024)

Internet

receiver

FA

HA

MN

home network

foreign

network

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)

MIP reverse tunneling is backwards compatible

the extensions can be implemented easily and cooperate with current

implementations of Mobile IP without these extensions

agent advertisements can carry requests for reverse tunneling


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)

handover 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


Changes with IPv6

Huge address space with IPv6 address renumbering scheme

Better mobility support

Mobile IP was designed as add-on to IPv4

majority of IPv4 nodes do not support Mobile IP

MN can use Address Autoconfiguration which eliminates the need of a Foreign Agent

Stateless: to configure its care-of address from a NW prefix of the foreign NW and a MN interface identifier. The needed information is published by neighboring routers through the Neighbor Discovery protocol in the foreign network (combined ARP/ICMP)

Statefull: by using a centralized DHCP server

Source Routing: Instead of tunneling packets using “IP in IP”, IPv6 Routing Headers are used

IPv6 does work smoothly with Ingress filtering

In IPv4 a border router may discard IP packets not originating from its own subnet, and MN use their home address always as source address

Every IPv6 node will have implemented IPv6 authentication headers to be used with binding updates


Tunneling Operation (IPv6)

Route Optimization: Only the MN can send a binding update, e.g. to the CN. If the CN knows the care-of address of the MN it can prevent triangle routing through the HA

Tunneling is facilitated using routing headers and not “IPv6 in IPv6”

No problems if the MN moves to another FA, as IPv6 requires that binding messages have to be send by the MN to the CN and HA directly every time the MN moves

IPv6 uses destination option headers to include the binding update in a normal IPv6 packet

Home network

Foreign network

Home Agent

Mobile Node

1. CN sends IP

packet to home

address of MN

Correspondent

Node

3. Strips off the tunnel header

and reads the packet

4. The MN sees that the packet

was routed through the HA

and therefore can send a

binding update to the CN

directly

5. The CN afterwards can send

packets directly to the CN by

using Routing headers

2. HA adds a routing header with the

care-of address as destination.


Moving to a new Location (IPv6)

All Binding Update messages intended for the CN are transmitted directly by the

MN. This becomes feasible as IPv6 uses destination option headers to include

the binding update in a normal IPv6 packet, e.g. in TCP ACK messages

Thus corresponding nodes are generally kept updated and can send nearly every

packet directly to the MN

Home network

New Foreign network

Home Agent

Mobile Node

Correspondent

Node

Situation after the MN has

moved to a new subnetwork

3. The CN again can send

packets directly to the CN by

using IPv6 Routing headers

2. MN also sends a Binding Update directly to

the CN

1. MN sends a Binding Update directly to the HA


Problems of Mobile IP

Security and Privacy

authentication with FA problematic where the FA belongs to another

organization

no protocol for key management and key distribution has been standardized

in the Internet (manual key distribution)

combination with IPsec is problematic (tunnel within tunnel)

no location privacy

Firewalls

typically Mobile IP cannot be used together with firewalls, special set-ups are

needed (such as reverse tunneling)

QoS

QoS needs to go in line with mobility support (handover requires update of

location information as well as QoS information)

Security, firewalls, QoS etc. are topics of current research and discussions!


Dynamic Host Configuration Protocol (DHCP)

Application

simplification of installation and maintenance of networked

computers

supplies systems with all necessary information, such as IP

address, DNS server address, domain name, subnet mask, default

router etc.

enables automatic integration of systems into an Intranet or the

Internet

can be used to acquire a COA for Mobile IP (co-location of MN and

FA)

Client/Server-Model

the client sends via a MAC broadcast a request to the DHCP server

(might be via a DHCP relay)

client relay

client DHCP server

DHCPDISCOVER

DHCPDISCOVER


DHCP – protocol mechanisms

server

(not selected) client server

(selected)

initialization

collection of replies

selection of configuration

initialization completed

release

confirmation of

configuration

delete context

determine the

configuration

DHCPDISCOVER

DHCPOFFER

DHCPREQUEST

(reject)

DHCPACK

DHCPRELEASE

DHCPDISCOVER

DHCPOFFER

DHCPREQUEST

(options)

determine the

configuration


DHCP characteristics

Server

several servers can be configured for DHCP, coordination not yet

standardized (i.e. manual configuration)

Renewal of configurations

IP addresses have to be requested periodically, simplified protocol

Options (RFC 2132)

available for routers, subnet mask, NTP (network time protocol)

timeserver, SLP (service location protocol) directory,

DNS (domain name system)

Big security problems!

no authentication of DHCP information specified


References

Books and Presentations

Jochen Schiller: Mobile Communications (German and English), Addison-

Wesley, 2000 (chapter 9 provides an overview on Mobile IP)

Charles Perkins: Mobile IP – Design Principles and Practises. Addisson

Wesley, 1998

Ramjee Prasad, Marina Ruggieri: Technology Trends in Wireless

Communications, Artech House, 2003

Wisely, Eardley, Burness: IP for 3G: Networking Technologies for Mobile

Communications, Wiley, 2002 (chapter 5 provides classification of mobility

mechanisms and overview on protocols, including session-layer mobility)

Important standards:

Mobile IP: RFC 3220, formerly: RFC 2002

Reverse tunneling: RFC 3024, formerly: 2344

DHCP: RFC 2131, RFC 2132

ICMP: RFC 1256

Documents

Mobility Management - Startseite TU Ilmenau