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Department of Computer Sciences THE UNIVERSITY OF TEXAS AT AUSTIN CS 395T - Mobile Computing and Wireless Networks Mobile Networking (I) © 2002 Yongguang Zhang Contents • Mobility at the Network Layer • IETF Mobile-IP – Other Mobile-IP • Discussions – Architectural issues – Common implementation issues • Future Directions Spring 2002 © 2002 Yongguang Zhang 2 Mobility at the Network Layer • Where can you manage mobility? – – – – – – Application Session Transport Network Data-link Physical • Mobile-IP: an extension to current IP architecture – To manage mobility at the IP layer – To hide mobility from the upper layers Spring 2002 © 2002 Yongguang Zhang 3 Terminology • • • • Mobile Node (MN or MH) Correspondent Node (CN or CH) Home Network and Foreign Network Mobility Agent – Home Agent (HA) and Foreign Agent (FA) • Home Address (HoA) and Care-of Address (CoA) • Binding and Binding Update Spring 2002 © 2002 Yongguang Zhang 4 IETF Mobile-IP: Basic Concept • MN always uses its home address HoA • When MN visits a foreign network, – Registration with FA • Discover mobile agents and CoA – Registration with HA • Binding update (HoA -> CoA) • When CN communicates with MN, it uses HoA • HA forwards packet from HoA to CoA Spring 2002 © 2002 Yongguang Zhang 5 Agent Discovery • Through Agent Discovery Process • Agent advertisement (beaconing): – Mobile agent broadcast agent advertisement at regular intervals (“I am here”) • Agent solicitation: – MN can solicit advertisement (“anyone here?”) – Mobile agent respond to agent solicitation • Question: – why agent solicitation? Spring 2002 © 2002 Yongguang Zhang 6 Functions of Agent Advertisement • Allow for the detection of mobility agents • Let the MN know whether the agent is a HA, or a FA • List one or more available care-of addresses • Inform the MN about special features provided by FA – Example: Alternative encapsulation techniques • Let MN determine the network number and status of their link to the Internet Spring 2002 © 2002 Yongguang Zhang 7 CoA • Two types of CoA: – FA’s IP address – MN’s temporary address • Locally-assigned address in the foreign network • E.g., DHCP address • Depends on foreign network configuration – Foreign network may or may not hand out addresses to visitors Spring 2002 © 2002 Yongguang Zhang 8 Implementing Agent Discovery • Protocol details – Built on top of an existing standard protocol: Router Advertisement (RFC 1256) – Simply extends the fields of existing router advertisements Spring 2002 © 2002 Yongguang Zhang 9 Registering CoA • HA must know a MH’s CoA (binding update) • Binding: (HoA->CoA) – Binding has a lifetime (can expire) • Registration process – – – – – MH sends a registration request with CoA information HA authenticate the request HA approves or disapproves the request HA adds the necessary information to its routing table HA sends a registration reply back to MH Spring 2002 © 2002 Yongguang Zhang 10 Registration Operations Spring 2002 © 2002 Yongguang Zhang 11 Authentication • A malicious node could cause remote redirect • Authentication and protection against replay attacks, and need for unique identification field – Timestamp and Pseudorandom Number Spring 2002 © 2002 Yongguang Zhang 12 Automatic Home Agent Discovery • Problem: what if MH never knew its HA? – Example: MH reboots and losses all states • Subnet-wise broadcast packet is sent to the home network – Subnet-wise broadcast: cell-cast • HA responds • If more than one, other HAs on the home network send rejection notice Spring 2002 © 2002 Yongguang Zhang 13 Forwarding to CoA • Encapsulation – Sending the original packet (CH->MH) in another packet (HA->CoA) • Default encapsulation mechanism: – IP-within-IP (tunnel) – Tunnel header: A new IP header inserted by the tunnel source (home agent) – Destination IP: CoA • Alternative encapsulation mechanism: – Minimal encapsulation Spring 2002 © 2002 Yongguang Zhang 14 Tunneling Operations in Mobile IP Spring 2002 © 2002 Yongguang Zhang 15 The Triangle Routing Problem • MH->CH: direct; CH->MH: CH->HA->MH – Inefficient • Solution: Route optimization in Mobile-IP – Deliver binding updates directly to CH Spring 2002 © 2002 Yongguang Zhang 16 Discussion • System issues Spring 2002 © 2002 Yongguang Zhang 17 Home Network • Where Can We Put the Home Agent? – At the router? – As a separate server? • At the router – What if there is multiple routers for the home network? • As a separate server – How can it pick up a packet [CHMH]? Spring 2002 © 2002 Yongguang Zhang 18 Foreign Network • Where is FA? (Router or Separated Server?) • How Can FA deliver MH the packet [CHMH] – Normally, [CHMH] would go straight to a router (because MH is foreign) • Is There Adequate Support at A Foreign Network – What if there is no FA at the network you visit? – Co-located FA • What is the Minimum Requirement from the Foreign Network? – Keep it as small as possible Spring 2002 © 2002 Yongguang Zhang 19 Security Issues • Visitors Are Threats! – How to provision your LAN to support nomadic users – And to protect your LAN from nomadic users • Foreign Network Firewall Traversal – Can firewall allows inbound [HAFA] tunnel? – Can [MHCH] pass through an egress filter? • Bi-directional tunneling • Mutual Authentication – Can you trust MH? – Can you trust FA? Spring 2002 © 2002 Yongguang Zhang 20 Mobile Computing Model • What is the binding in IETF Mobile-IP? – HoA -> CoA (one level of indirection) • Where is the binding being managed? – HA – In the route optimization case: CH • Scale of mobility? – Internet-wide • What is a cell in Mobile-IP? – Subnet Spring 2002 © 2002 Yongguang Zhang 21 Further Discussions • Variants of IETF Mobile-IP – Implementation issues • Mobility Scope – Macro-mobility: Mobile-IP – Micro-mobility: Hierarchical Mobile-IP, Cellular-IP, HAWAII, TeleMIP, EMA, … • Combining network-layer mobility with link-layer mobility • Features: fast handoff, paging, etc. • Mobility in a higher layer – Transport layer, session layer Spring 2002 © 2002 Yongguang Zhang 22 Summary • • • • IETF Mobile-IP Other versions of Mobile-IP Other extensions to Mobile-IP Future Directions Spring 2002 © 2002 Yongguang Zhang 23