What we will cover…Home Networking: Network Address Translation (NAT)Mobile Routing

Home network

local network(e.g., home network)

rest ofInternet

NAT: Network Address Translation

10.0.0.1

10.0.0.2

10.0.0.3

10.0.0.4

138.76.29.7

local network(e.g., home network)

10.0.0/24

rest ofInternet

Datagrams with source or destination in this networkhave 10.0.0/24 address for

source, destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address: 138.76.29.7,different source port numbers

NAT: Network Address Translation

Advantages:

local network uses just one IP address as far as outside world is concerned: min. IP address wastage

can change addresses of devices in local network without notifying outside world: flexibility

devices inside local net not explicitly addressable, visible by outside world (a security plus).

NAT: Network Address Translation

Implementation: NAT router must:

outgoing datagrams: replace (source IP address, port #) of every outgoing datagram to (NAT IP address, new port #). . . remote clients/servers will respond using (NAT IP

address, new port #) as destination addr.

remember (in NAT translation table) every (source IP address, port #) to (NAT IP address, new port #) translation pair

incoming datagrams: replace (NAT IP address, new port #) in dest fields of every incoming datagram with corresponding (source IP address, port #) stored in NAT table

NAT: Network Address Translation

10.0.0.1

10.0.0.2

10.0.0.3

S: 10.0.0.1, 3345D: 128.119.40.186, 80

1

10.0.0.4

138.76.29.7

1: host 10.0.0.1 sends datagram to 128.119.40.186, 80

NAT translation tableWAN side addr LAN side addr

138.76.29.7, 5001 10.0.0.1, 3345…… ……

S: 128.119.40.186, 80 D: 10.0.0.1, 3345

4

S: 138.76.29.7, 5001D: 128.119.40.186, 80

2

2: NAT routerchanges datagramsource addr from10.0.0.1, 3345 to138.76.29.7, 5001,updates table

S: 128.119.40.186, 80 D: 138.76.29.7, 5001

3

3: Reply arrives dest. address: 138.76.29.7, 5001

4: NAT routerchanges datagramdest addr from138.76.29.7, 5001 to 10.0.0.1, 3345

NAT: Network Address Translation

16-bit port-number field: 60,000 simultaneous connections with a

single LAN-side address!

NAT traversal problem client wants to connect to

server with address 10.0.0.1 server address 10.0.0.1 local

to LAN (client can’t use it as destination addr)

only one externally visible NATted address: 138.76.29.7

solution 1: statically configure NAT to forward incoming connection requests at given port to server e.g., (123.76.29.7, port

2500) always forwarded to 10.0.0.1

10.0.0.1

10.0.0.4

NAT router

138.76.29.7

Client?

NAT traversal problem solution 2: relaying (used in Skype)

NATed client establishes connection to relay

External client connects to relay relay bridges packets between connections

138.76.29.7

Client

10.0.0.1

NAT router

1. connection torelay initiatedby NATted host

2. connection torelay initiatedby client

3. relaying established

NAT: Network Address Translation

NAT is controversial:

routers should only process up to layer 3

NAT breaks that protocol!!!

Mobile Routing

What is mobility?

spectrum of mobility, from the network perspective:

no mobility high mobility

mobile user, usingsame 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: Vocabularyhome network: permanent “home” of mobile(e.g., 128.119.40/24)

Permanent address: address in home network, can always be used to reach mobilee.g., 128.119.40.186

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

wide area network

correspondent

Mobility: more vocabulary

Care-of-address: address in visited network.(e.g., 79,129.13.2)

wide area network

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

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

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

correspondent: wants to communicate with mobile

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: 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

End result: Foreign agent knows about mobile Home agent knows location of mobile

wide area network

home network

visited network

1

mobile contacts foreign agent on entering visited network

2

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

Mobility via Indirect Routing

wide area network

homenetwork

visitednetwork

3

2

41

correspondent addresses packets using home address of mobile

home agent intercepts packets, forwards to foreign agent

foreign agent receives packets, forwards to mobile

mobile replies directly to correspondent

Forwarding datagrams to remote mobile

Permanent address: 128.119.40.186

Care-of address: 79.129.13.2

dest: 128.119.40.186

packet sent by correspondent

dest: 79.129.13.2 dest: 128.119.40.186

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

dest: 128.119.40.186

foreign-agent-to-mobile packet

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

Mobility via Direct Routing

wide area network

homenetwork

visitednetwork

4

2

41correspondent requests, receives foreign address of mobile

correspondent forwards to foreign agent

foreign agent receives packets, forwards to mobile

mobile replies directly to correspondent

3

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?