MOB 6 addressing routing 2010

Internet & Mobile Communications - 2007 10 DHCP  Dialog with the server – Ports’ numbers:  The client only uses port 68 to send and receive its messages  The server sends and re

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Anne Fladenmuller Internet & Mobile Communications - 2007

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Internet & Mobile Communications - 2007

Goal: routing and IP packets control

Operations taken into account by IP:

Mobility requires modifications mainly in packets

redirection functions

• QoS management

• Triggering of address resolution mechanisms

• Information about control and links state

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…

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WAN

98.217.15.25

132.227.61.xx 98.217.15.xx

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Network Layer

  Different mobility aspects

–  Unfrequent moves from the user with his laptop or PDA

  IP address modification: DHCP

  Macro mobility management

–  Frequent moves from the user: micro mobility

management

–  Independant moves of all network devices: Ad Hoc networks

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DHCP

  Allocation of a new IP address with DHCP

(Dynamic Host Configuration Protocol)

–  Main goal:

  Simplification of network administration

with his computer

–  It allows obtaining a network configuration dynamically:

  DHCP is mainly used for IP addresses distribution

  It comes from an evolution of BOOTP (Bootstrap Protocol) used to set up machines accross a network

configuration parameters specific to a given host

  RFCs: 1541

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DHCP

  DHCP protocols principles

–  1 DHCP server distributes IP addresses

  The server is a base for all DHCP requests (1 server with a fixed IP address per network)

–  When a machine gets started, it has no information about its network configuration

–  To find the DHCP server and dialog with it, the machine will send a particular broadcast packet on the LAN

–  When the DHCP server receives this packet, it answers with another broadcast packet (the client does not necessarily have his IP address and is thus unreacheable directly) which contains all necessary information for the client

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DHCP

  Allocation of a static or dynamic address

–  A DHCP server generally provides dynamic addresses

  A same computer can thus receive 2 different addresses one successively

–  But it can also provide a fixed IP address to a specific client

  This must be used reasonably, otherwise the DHCP server is more or less useless

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DHCP

  Dialog with the server

–  Ports’ numbers:

  The client only uses port 68 to send and receive its messages

  The server sends and receives its messages on a single port, port 67

  The DHCP frame is indeed the same as BOOTP

  Parameters exchange (machine’s name ) is done through options

–  Options are described in RFC2132 They are all identified by a number For example,

  option 15: provides the client with the network’s domain name

  option 53: DHCPACK

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DHCP

 op: equals 1 for BOOTREQUEST

(client request), 2 for BOOTREPLY

(server answer)

  htype: type of hardware address

  hlen: length of hardware address (in

bytes) It is 6 for a MAC address

  hops: can be used by DHCP relays

 xid: random number chosen by the

client and used to recognize the

client

 secs: time spent (in seconds) since

the client started its request

  flags: various flags

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DHCP

ciaddr: client’s IP address, when he

already has one

yiaddr: the (future) client’s IP address

siaddr: IP address of the (next) server

to use

giaddr: relay’s IP address (e.g

gateway) when the direct client/server

connection is not possible

chaddr: client’s hardware address

sname: optional field Server’s name

file: name of the file that should be

used to boot

options: Reserved field for options A

DHCP client must be ready to receive

at least 576 bytes, but it can ask the

server to limit the size of its messages

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  DHCPOFFER (2) answer of a server to a DHCPDISCOVER

message, which contains the first parameters

  DHCPREQUEST (3) client request e.g to extend its lease

  DHCPDECLINE (4) the client tells the server that the address is

already used

  DHCPACK (5) answer from the server which contains the client’s

parameters and address

  DHCPNAK (6) server’s answer to tell the client that its lease has

expired or if the client announces a worng network configuration

  DHCPRELEASE (7) the client releases its IP address

  DHCPINFORM (8) the client asks for local parameters, it already

has its IP address

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propose an IP address to the client (among others)

  The client sets up its configuration, then makes a

DHCPREQUEST to validate its IP address (broadcast

request because DHCPOFFER does not contain its IP

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DHCP

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DHCP

–  In order to optimize network resources, IP addresses are allocated with a starting and an end validity date: a lease

with a validity period, but also other configuration information like:

–  DNS address (Name resolution)

–  Default Gateway address (to get out of the network where the DHCP server has set up the client)

–  The DHCP server address

  The lease may be extended on the client’s request or on the server’s proposal If the server does not receive any valid answer, it makes the IP address available

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DHCP

  Optimization of IP addresses allocation by modifying the leases’ duration

–  The problem is here:

  If all addresses are allocated and none is released after a certain time, no more request will be satisfied

–  In a network to which many computers connect frequently, it is interesting to propose short leases But be careful not to block the bandwidth on the small and very busy networks

–  In a network mostly constituted of fixed machines very rarely rebooted, long leases are sufficient

  It is recommended not to create unnecessarily short leases, which leads to a significant increase in the network A

compromise must be found between the mean users’ connection suration, the server’s number of IP addresses left, the number of subscribers

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DHCP

  Lease expiration

–  DHCP is preventive: it waits until 50% of the lease’s duration

to ask for its extension

  To do this the client contact the original server through a (DHCPREQUEST) message

  If the leas eextension is accepted by the server, it send a (DHCPACK) message so that the client can be updated with this new duration

–  If the client does not get any answer il will wait 7/8th of the lease’s duration and will ask its DHCP server, if it can extend its lease’s duration

  DHCP servers can answer with a (DHCPACK) to extend the client’s lease

  If a server cannot extend its lease, it will send a (DHCPNACK) message to the client who will have to restart the whole IP lease request procedure

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DHCP

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–  Negociation is done as follows:

another nework, they must thus cross routers (theoretically impossible)

  Installation on one or several routers of a relay agent who will intercept bradcast requests and will forward them to a DHCP server known by this agent

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DHCP

–  The relay agent located on the gateway will be the intermediary and the client will however manage to get an address, given by a DHCP server located on another network, but relayed by the relay agent

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DHCP/DNS

  Operation of DHCP/DNS update

(PTR) and addresses (A) resources for its activated DHCP clients

–  This process requires the use of a additional DHCP option: the FQDN client option (option 81)

  This option allows the client to provide the DHCP server with:

–  Its complete domain name (FQDN) ,

–  Instructions on the way it wants the server to process the dynamic DHCP updates about itself (should this happen)

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DHCP/DNS

  The server can be configured in various ways

to process clients’ requests:

–  The DHCP server keeps and updates client’s information from its DNS servers in accordance with the client’s request

–  The DHCP server always saves and updates the client’s information from its configured DNS servers

–  The DHCP server never saves and updates the client’s information from its configured DNS servers

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Internet & Mobile Communications - from Gwendal Legrand

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–  “on-the-go”, e.g., while sitting on a train;

–  possibility of network connections remaining open

–  Mobile Computers (Mobile IP, IEEE 802.11)

–  Mobile Networks (Ad-hoc Network)

  Ubiquitous computing:

–  computing everywhere… OR

–  computers everywhere…most of them invisible

–  hundreds of computers per person, various sizes and capabilities

–  Characteristics

  very small smart badge w/ user info, etc

  allow personalized settings to follow a user

  attached to anything books, car keys, etc.

  Need of service location protocols

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IP mobility vs Wireless LANs

on the same IP subnet)

  IP mobility is not equal to

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Requirements of the IP mobility architecture

  Two major requirements arise when

the access network used by the mobile roaming user

  Dealing with mobility at the IP layer provides a way to answer the above requirements

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Mobility in the Internet

  IP address

–  used as a routing directive

–  used as an end-point identifier

  TCP transport session

–  4-tuple: <src addr, src port, dest addr, dest port>

  Host moves

–  get a new address -> translate addresses

–  keep its address -> change routing

  Let's see that in more detail now …

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Mobile IP standardization process

  Standardization of Mobile IP is carried out at the IETF

–  The IP Routing for Wireless/Mobile Hosts

(mobileip) Working Group is in charge of defining and

specifying the Mobile IP architecture and protocols

  Some very interesting enhanced functionalities are still considered as work in progress and specified in Internet Drafts

found at the mobileip WG home page on the Web: http://

www.ietf.org/html.charters/mobileip-charter.html

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I wonder where Alice moved to?

Consider friend frequently changing

addresses, how do you find her?

How do you contact a mobile friend:

  search all phone

books?

  call her parents?

  expect her to let you

know where he/she is?

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network, can always be

used to reach mobile

e.g., 137.194.160.36

home agent: entity that will perform mobility functions on behalf of mobile, when mobile

is remote

wide area network

correspondent

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visited network: network

in which mobile currently resides (e.g., 132.227.61.0)

Permanent address: remains constant (e.g., 137.194.160.36)

foreign agent: entity

in visited network that performs mobility functions on behalf of mobile

outside its home network

Home agent : entity in the home network which delivers datagrams

to departed mobile nodes, and maintains

current location information for each

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The Mobile IP basic concept

  The Mobile IP architecture resolves the above

contradiction by using 2 IP addresses for a mobile host :

identify uniquely the IP host on the Internet (answers the two first IP addresses constraints)

route the datagrams destined to the mobile host to the current attachment point of this host (answers the last IP addresses constraint)

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Mobility: approaches

  Let routing handle it: routers advertise permanent

address of mobile-nodes-in-residence via usual routing table exchange

–  routing tables indicate where each mobile located

–  no changes to end-systems

  Let end-systems handle it:

–  indirect routing: communication from correspondent

to mobile goes through home agent, then forwarded

to remote

–  direct routing: correspondent gets foreign address of mobile, sends directly to mobile

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Mobility: approaches

address of mobile-nodes-in-residence via usual routing table exchange

–  routing tables indicate where each mobile located

–  no changes to end-systems

  let end-systems handle it:

–  indirect routing: communication from correspondent

to mobile goes through home agent, then forwarded

to remote

–  direct routing: correspondent gets foreign address of mobile, sends directly to mobile

not scalable

to millions of mobiles

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Some open questions … for the moment

  How does the mobile host get a COA?

–  Router advertisements, DHCP, manual

  How can a mobile host tell where it is?

–  Am I at home?

–  Am I visiting a foreign network?

–  Have I moved?

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Home Agent

Foreign Agent

Agent advertisement

Home Address → Care-of Address

Tunnel

header

IPsrc = Home Agent

IPDst = Foreign Agent

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Protocol overview

  Home Agent & Foreign Agent broadcast or multicast agent

advertisements on their respective links

contents of these advertisements to determine whether they are on the home or on a visited network

  A mobile node on a visited network acquires a temporary address (care

of address) – DHCP

  The mobile registers its COA with its home agent

The packets for the mobile are intercepted and sent to the current

position of the mobile

  The packets arrive to the COA and are decapsulated in order to extract the original packet

  The packets from the mobile are sent directly to the correspondents

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  Registration :

–  When a mobile is away, it registers its temporary address with its home agent

  Tunneling :

–  The packets for the mobile are intercepted by the

HA and tunnelled to the mobile

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  Based on 2 types of messages:

–  Agent Advertisement : broadcast or multicast by

the agents

–  Agent Solicitation : sent by a mobile which does

not want to wait for an AA

  Message authentication needed

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