Icmp internet control message protocol
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used by hosts, routers, gateways to communication network-level information error reporting: unreachable host, network, port, protocol echo request/reply (used by ping) network-layer “above” IP: ICMP msgs carried in IP datagrams

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ICMP: Internet Control Message Protocol

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Icmp internet control message protocol

used by hosts, routers, gateways to communication network-level information

error reporting: unreachable host, network, port, protocol

echo request/reply (used by ping)

network-layer “above” IP:

ICMP msgs carried in IP datagrams

ICMP message: type, code plus first 8 bytes of IP datagram causing error

ICMP: Internet Control Message Protocol

TypeCodedescription

0 0 echo reply (ping)

3 0 dest. network unreachable

3 1 dest host unreachable

3 2 dest protocol unreachable

3 3 dest port unreachable

3 6 dest network unknown

3 7 dest host unknown

4 0 source quench (congestion

control - not used)

8 0 echo request (ping)

9 0 route advertisement

10 0 router discovery

11 0 TTL expired

12 0 bad IP header


Dhcp dynamic host configuration protocol

DHCP: Dynamic Host Configuration Protocol

Goal: allow host to dynamically obtain its IP address from network server when it joins network

Can renew its lease on address in use

Allows reuse of addresses (only hold address while connected an “on”

Support for mobile users who want to join network (more shortly)

DHCP overview:

  • host broadcasts “DHCP discover” msg

  • DHCP server responds with “DHCP offer” msg

  • host requests IP address: “DHCP request” msg

  • DHCP server sends address: “DHCP ack” msg


Dhcp client server scenario

E

B

A

DHCP client-server scenario

223.1.2.1

DHCP

223.1.1.1

server

223.1.1.2

223.1.2.9

223.1.1.4

223.1.2.2

arriving DHCP

client needs

address in this

network

223.1.1.3

223.1.3.27

223.1.3.2

223.1.3.1


Dhcp client server scenario1

DHCP discover

src : 0.0.0.0, 68

dest.: 255.255.255.255,67

yiaddr: 0.0.0.0

transaction ID: 654

DHCP client-server scenario

arriving

client

DHCP server: 223.1.2.5

DHCP offer

src: 223.1.2.5, 67

dest: 255.255.255.255, 68

yiaddrr: 223.1.2.4

transaction ID: 654

Lifetime: 3600 secs

DHCP request

src: 0.0.0.0, 68

dest:: 255.255.255.255, 67

yiaddrr: 223.1.2.4

transaction ID: 655

Lifetime: 3600 secs

time

DHCP ACK

src: 223.1.2.5, 67

dest: 255.255.255.255, 68

yiaddrr: 223.1.2.4

transaction ID: 655

Lifetime: 3600 secs


What is mobility

no mobility

high mobility

What is mobility?

  • spectrum of mobility, from thenetwork perspective:

mobile user, using

same access point

mobile user, passing through multiple access point while maintaining ongoing connections (like cell phone)

mobile user, connecting/ disconnecting from network using DHCP.


Mobility vocabulary

Mobility: Vocabulary

home network: permanent “home” of mobile

(e.g., 128.119.40/24)

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

wide area network

Permanent address: address in home network, can always be used to reach mobile

e.g., 128.119.40.186

correspondent


Mobility more vocabulary

Mobility: more vocabulary

visited network: network in which mobile currently resides (e.g., 79.129.13/24)

Permanent address: remains constant (e.g., 128.119.40.186)

Care-of-address: address in visited network.

(e.g., 79,129.13.2)

wide area network

home agent: entity in visited network that performs mobility functions on behalf of mobile.

correspondent: wants to communicate with mobile


How do you contact a mobile friend

How do you contact a mobile friend:

  • search all phone books?

  • call her parents?

  • expect her to let you know where he/she is?

I wonder where Alice moved to?

Consider friend frequently changing addresses, how do you find her?


Mobility approaches

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


Mobility approaches1

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

not

scalable

to millions of

mobiles


Mobility registration

mobile contacts foreign agent on entering visited network

foreign agent contacts home agent home: “this mobile is resident in my network”

1

2

Mobility: registration

visited network

home network

End result:

  • Foreign agent knows about mobile

  • Home agent knows location of mobile

wide area network


Mobility via indirect routing

foreign agent receives packets, forwards to mobile

home agent intercepts packets, forwards to foreign agent

correspondent addresses packets using home address of mobile

mobile replies directly to correspondent

3

2

4

1

Mobility via Indirect Routing

visited

network

home

network

wide area network


Indirect routing comments

Indirect Routing: comments

  • Mobile uses two addresses:

    • permanent address: used by correspondent (hence mobile location is transparent to correspondent)

    • care-of-address: used by home agent to forward datagrams to mobile

  • foreign agent functions may be done by mobile itself

  • triangle routing: correspondent-home-network-mobile

    • inefficient when

      correspondent, mobile

      are in same network


Forwarding datagrams to remote mobile

foreign-agent-to-mobile packet

packet sent by home agent to foreign agent: a packet within a packet

dest: 128.119.40.186

dest: 128.119.40.186

dest: 128.119.40.186

packet sent by correspondent

dest: 79.129.13.2

Forwarding datagrams to remote mobile

Permanent address: 128.119.40.186

Care-of address: 79.129.13.2


Indirect routing moving between networks

Indirect Routing: moving between networks

  • suppose mobile user moves to another network

    • registers with new foreign agent

    • new foreign agent registers with home agent

    • home agent update care-of-address for mobile

    • packets continue to be forwarded to mobile (but with new care-of-address)

  • Mobility, changing foreign networks transparent: on going connections can be maintained!


Mobility via direct routing

foreign agent receives packets, forwards to mobile

mobile replies directly to correspondent

4

2

4

1

3

Mobility via Direct Routing

correspondent forwards to foreign agent

visited

network

home

network

wide area network

correspondent requests, receives foreign address of mobile


Mobility via direct routing comments

Mobility via Direct Routing: comments

  • overcome triangle routing problem

  • non-transparent to correspondent: correspondent must get care-of-address from home agent

    • What happens if mobile changes networks?


Mobile ip

Mobile IP

  • RFC 3220

  • has many features we’ve seen:

    • home agents, foreign agents, foreign-agent registration, care-of-addresses, encapsulation (packet-within-a-packet)

  • three components to standard:

    • agent discovery

    • registration with home agent

    • indirect routing of datagrams


Mobile ip agent discovery

Mobile IP: agent discovery

  • agent advertisement: foreign/home agents advertise service by broadcasting ICMP messages (typefield = 9)

H,F bits: home and/or foreign agent

R bit: registration required


Mobile ip registration example

Mobile IP: registration example


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