Mobility: §7.5 & §7.6 Smith College, CSC 249 April 5, 2018 Overview Wireless – addressing and frame structure Mobility Within a single subnet Between subnets Mobility vocabulary Acting out mobility 2 1
Wireless: 802.11 frame: addressing 6 4 2 2 6 6 6 2 0 - 2312 address address address address payload CRC 1 2 3 4 Address 4: used only in ad hoc mode Address 1: MAC address of wireless host or AP Address 3: MAC address to receive this frame of router interface to which AP is attached Address 2: MAC address of wireless host or AP transmitting this frame 3 802.11 frame: addressing Internet router H1 R1 AP R1 MAC addr H1 MAC addr dest. address source address 802. 3 frame AP MAC addr H1 MAC addr R1 MAC addr Router interface Wireless Wireless destination source 802. 11 frame station station 4 2
802.11: mobility within same subnet H1 remains in same IP router subnet: IP address will remain same hub or switch How does the switch find H1 as it changes BBS 1 association from AP1 to AP 1 AP2? AP 2 self-learning: switch will see H1 BBS 2 frame from H1 and “remember” which switch port can be used to reach H1 5 Mobility: Vocabulary home network: permanent home agent: entity that will “home” of mobile perform mobility functions on (e.g., 128.119.40/24) behalf of mobile, when mobile is remote wide area network Permanent address: address in home network, can always be used to reach mobile correspondent e.g., 128.119.40.186 6 3
Mobility: more vocabulary visited network: network Permanent address: remains in which mobile currently constant ( e.g., 128.119.40.186) resides (e.g., 79.129.13/24) Care-of-address: address in visited network. (e.g., 79,129.13.2) wide area network foreign agent: entity in visited network that performs correspondent: wants mobility functions on to communicate with behalf of mobile. mobile 7 Mobility: Registration Protocols needed: 1) Mobile node to foreign agent – mobile node registers when enters a foreign network and deregisters when leaves 2) Foreign agent to home agent registration – foreign agent registers the COA with the home agent à No deregistration of COA, because _?_ 3) Home agent datagram encapsulation – datagram within a datagram, addressed to COA (‘tunneling’) 4) Foreign agent decapsulation – extract original datagram and forward to mobile node 8 4
Mobility: Registration home network visited network 1 2 Mobile contacts foreign agent contacts home foreign agent on agent: “this mobile is resident in entering visited my network” network. How End result: does it know to Foreign agent knows about mobile do this!? Home agent knows location of mobile 9 Mobility via Indirect Routing foreign agent receives packets, home agent intercepts forwards to mobile visited packets, forwards to foreign agent network home network 3 wide area network 2 1 4 correspondent addresses packets mobile replies using home address directly to of mobile correspondent 10 5
Indirect Routing: comments Mobile node has 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) 11 Mobile IP Built upon Indirect Routing: home agents, foreign agents, foreign-agent registration, care-of-addresses, encapsulation (packet-within-a-packet) Three components in the standard: 1. agent discovery (using ICMP) 2. registration with home agent (handshaking) 3. indirect routing of datagrams 12 6
Mobile IP agent discovery, ICMP Agent advertisement: foreign/home agents advertise service by broadcasting ICMP messages (typefield = 9) 16 0 8 24 type = 9 c hecksum code = 0 = 9 = 9 standard ICMP fields router address length sequence # RBHFMGV registration lifetime reserved bits mobility agent advertisement 0 or more care-of- extension addresses 13 ICMP: internet control message protocol Type Code description Used by hosts & routers to 0 0 echo reply (ping) communicate network-level 3 0 dest. network unreachable information 3 1 dest host unreachable error reporting: unreachable 3 2 dest protocol unreachable host, network, port, protocol 3 3 dest port unreachable echo request/reply (used by ping) 3 6 dest network unknown 3 7 dest host unknown Network-layer “above” IP: 4 0 source quench (congestion ICMP messages are carried in control - not used) IP datagrams 8 0 echo request (ping) ICMP message: type, code plus first 8 bytes of IP datagram causing error 11 0 TTL expired 12 0 bad IP header 7
Act out Mobile IP Need: home agent, foreign agent and mobile node (i) Move to new network (ii) Register (iii) Receive and send messages (iv) Move to new network and register 15 Mobile IP: Registration Example visited network: 79.129.13/24 home agent foreign agent ICMP agent adv. HA: 128.119.40.7 COA: 79.129.13.2 Mobile agent COA: 79.129.13.2 MA: 128.119.40.186 … . registration req. registration req. COA: 79.129.13.2 HA: 128.119.40.7 COA: 79.129.13.2 MA: 128.119.40.186 HA: 128.119.40.7 Lifetime: 9999 MA: 128.119.40.186 identification:714 Lifetime: 9999 … . identification: 714 encapsulation format … . registration reply registration reply time HA: 128.119.40.7 MA: 128.119.40.186 HA: 128.119.40.7 Lifetime: 4999 MA: 128.119.40.186 Identification: 714 Lifetime: 4999 encapsulation format Identification: 714 … . … . 16 8
Mobile IP: Indirect Routing foreign-agent-to-mobile packet packet sent by home agent to foreign dest: 128.119.40.186 agent: a packet within a packet dest: 79.129.13.2 dest: 128.119.40.186 Permanent address: 128.119.40.186 Care-of address: 79.129.13.2 dest: 128.119.40.186 packet sent by correspondent 17 Mobile IP Question Consider two mobile nodes in a foreign network having a foreign agent. Is it possible for the two mobile nodes to use the same care- of-address in mobile IP? Explain Yes – COA can simply be the foreign agent (foreign router) 18 9
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 19 Wireless, Mobility: Impact on Higher Layer Protocols Logically, impact should be minimal … Best effort service model remains unchanged TCP and UDP can (and do) run over wireless, mobile … but performance-wise: Packet loss/delay may increase TCP interprets loss as congestion, will decrease congestion window un-necessarily Delay impairments for real-time traffic Limited bandwidth of wireless links 20 10
Chapter 7 Summary Wireless Mobility Wireless links: Indirect routing Link characteristics Elements (actors) Procedure Error prone – why? Mobile IP Network characteristics Impact on higher-layer IEEE 802.11 (“Wi-Fi”) protocols CSMA/CA – know collision avoidance rationale and implementation 21 On to Security 11
Network Security The principles of network security: Access & availability Cryptography, beyond “confidentiality” Message integrity Authentication Securing each layer 23 What is network security? Access and Availability: Confidentiality: Data Integrity: Authentication: 24 12
Friends and enemies: Alice, Bob, Trudy well-known in network security world Bob and Alice want to communicate “securely” Trudy (intruder) may intercept, delete, add and/or alter messages Who/what might Alice and Bob be? Alice Bob channel data, control messages secure secure data data sender receiver Trudy 26 Cryptographic Keys Alice’s Bob’s K K encryption A decryption B key key ciphertext encryption decryption algorithm algorithm plaintext plaintext Symmetric key cryptography: sender & receiver keys are identical and secret (but known by 2 parties) Public-key cryptography: the encryption key is public , the decryption key secret, and know only by one party 29 13
Symmetric Key Cryptography K K A-B A-B ciphertext plaintext plaintext encryption decryption message, m algorithm algorithm m = K ( ) K (m) K (m) A-B A-B A-B Symmetric key cryptography: Bob and Alice share/know the same (symmetric) key: K e.g., key is knowing substitution pattern in mono-alphabetic substitution cipher Q: 30 Public Key Cryptography + Bob’s public K B key - Bob’s private K B key plaintext ciphertext plaintext encryption decryption message message, m algorithm + algorithm K (m) - + m = K ( K (m) ) B B B 31 14
RSA Important Property The following property defines this method: - + - + K ( K (m) ) = m K ( K (m) ) = B B B B use public key use private key first, followed first, followed by public key by private key 32 15
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