Dallas, March 2006

1. Dallas, March 2006 IETF 65th – autoconf WG MANET connectivity scenarios and multiple gateways issues Simone Ruffino {simone.ruffino@telecomitalia.it}

2. Scenarios draft • draft-ruffino-autoconf-conn-scenarios-00 • Goals: • describe a set of scenarios of MANET connection to the Internet • provide a reference for AUTOCONF WG, to help finding a solution not tailored to one/two specific scenarios • Categorization based on gateways characteristics • Analysis ranges from no connectivity (e.g. isolated MANET) to more complex scenarios (e.g. multiple mobile Internet gateways) • No technical issues in the draft

3. Isolated MANET • No connection to external networks • All traffic is generated by MANET nodes and addressed to MANET nodes • Applications : • temporary networks, set-up in areas where neither wireless coverage nor infrastructure exist • emergency networks for disaster recovery • battlefield applications • occasional work meetings • file sharing among co-workers

4. Connected MANET • MANET nodes • exchange data traffic among themselves through multi-hop paths • communicate with hosts located in the external network, routing traffic towards a gateway • Internet Gateways (IGWs) • equipped with at least two network interfaces, one of which is connected to the MANET • receive traffic from outside hosts and route it to the destination MANET node www External IP Network … IGW IGW

5. Connected MANET - Fixed IGWsMesh networks External IP Network External IP Network AP/IGW AP/IGW IGW IGW AP AP AP AP AP AP

6. Connected MANET - Mobile IGWs Multi-hop cellular networks • Goal: coverage extension of cellular networks • GSM,GPRS,UMTS etc • Gateways are mobile • Nodes that are within coverage area can become gateways • Concurrently active multiple gateways Internet Cellular WAN

7. Intermittent connectionTrain networks • IGWs in a MANET, especially if mobile and equipped with a radio interface, may not be permanently connected to the external network • MANETs may experience a burst of exchanged traffic while connected to the external network Station Station

8. Internet Gateways • Gateways play a critical role • Depending on their characteristics, gateways: • could be dedicated devices, endowed with additional resources • could serve as enforcement point, ingress filtering, DNS etc. • could run an “external” routing protocol to announce internal routes to external routers and hosts • could also be normal MANET nodes (i.e. OCCASIONAL GATEWAYS) • Sometimes they could be small, mobile, low-powered devices (highly dynamic) • Gateways are the owners of topologically correct IPv6 prefixes, which can be assigned to MANET

9. Multiple IGWs MANET • Multiple gateways • Improve reliability and fault tolerance (no single point of failure) • Enable load balancing of traffic directed/coming to/from the Internet • Essential feature, because gateways can become bottlenecks, if the number of nodes in the MANET increases • this also depends on the available bandwidth on the uplink interface. • But, different design choices can bring some additional issues • Single vs. Multiple prefixes advertised by IGWs • Address choice impacts performances • Overhead of address uniqueness checks • See also • sec. 3 of draft-ruffino-manet-autoconf-multigw-02

10. Issue #1 • In case of multiple GWs announcing *one* network prefix, partitioning of the MANET may invalid routes in the Internet towards MANET nodes • E.g. if a MANET cloud breaks into two separate parts, each one containing a gateway, routers in the Internet cannot choose the correct gateway to deliver traffic for a MANET node • Solutions are possible, but currently there is no suitable IETF standard • Example solutions include: use of host routes, use of a signalling path through the Internet • Drawbacks: • solutions could require additional protocols/mechanism to run on Internet routers, gateways and MANET nodes • Applicability would be limited to scenarios with very limited mobility (i.e. no partitions)

11. Issue #2 • In case of multiple gateways advertising *multiple* network prefixes, no coordination among gateways is needed • Each gateway is the legitimate owner of one (or more) prefix • Nodes can configure multiple global addresses on MANET interfaces • Nodes' choice of source address affects the downstream data path within the MANET • traffic from the Internet is routed through the gateway which owns the prefix, used by nodes to build source address; • if nodes choose a prefix announced by a very "far" gateway (in terms of routing metrics) traffic could flow through a non-optimal path within the MANET • Source address selection (RFC3484) operates on a prefix longest match basis • It does not take into account *distance* (in terms of routing metric) between node and gateways

12. Routing dependance from address choice • Traffic coming from the Internet (green) • is directed to the gateway which owns the prefix used by nodes to configure their global addresses • can flow through many hops in the MANET although a better path could exist if a different GW were chosen for configuration • Low throughput, high latency and delay variation 2001:db8:0:a::/64 2001:db8:0:b::/64 2001:db8:0:a::1/64 2001:db8:0:a::1/64

13. Lower throughput due to sub optimal downlink path Routing dependance from address choice (cont.)

14. Issue #3 • MANET nodes could reconfigure (frequently) their global address(es), due to partitioning, merging and gateway failure. • draft-ietf-ipv6-rfc2462bis-08 states that • every unicast IPv6 address SHOULD be checked for uniqueness, prior to configuration • it is not reccommended to perform DAD only on link-local addresses and skip the test for global addresses which use the same Interface ID • In a multiple-gateway/multiple-prefixes MANET, this could bring to a large amount of control signalling, especially if the ad-hoc network is very dynamic.

15. Next steps • Revise and enhance draft-ruffino-autoconf-conn-scenarios-00, gathering more input on different scenarios/applications • Receive feedback on specific issues on multiple-gw/multiple-prefixes manet • Possible inclusion into the PS ? Thanks !