Transcript PPT Version

Dallas, March 2006
IETF 65th – autoconf WG
MANET connectivity scenarios
and multiple gateways issues
Simone Ruffino
{[email protected]}
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
S.Ruffino - Autoconf scenarios and multi-gw issues
March, 2006
IETF 65th – autoconf WG
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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
S.Ruffino - Autoconf scenarios and multi-gw issues
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Connected MANET
www
External
IP Network
IGW
…
IGW
• 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
S.Ruffino - Autoconf scenarios and multi-gw issues
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Connected MANET - Fixed IGWs
Mesh networks
External IP
Network
AP/IGW
AP/IGW
AP
External IP
Network
IGW
IGW
AP
AP
AP
AP
AP
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IETF 65th – autoconf WG
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Connected MANET - Mobile IGWs
Multi-hop cellular networks
• Goal: coverage
extension of cellular
networks
Internet
Cellular WAN
– GSM,GPRS,UMTS etc
• Gateways are mobile
• Nodes that are within
coverage area can
become gateways
– Concurrently active multiple
gateways
S.Ruffino - Autoconf scenarios and multi-gw issues
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Intermittent connection
Train networks
• IGWs in a MANET,
especially if mobile and
equipped with a radio
interface, may not be
permanently connected
to the external network
Station
• MANETs may
experience a burst of
exchanged traffic while
connected to the
external network
Station
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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
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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
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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)
S.Ruffino - Autoconf scenarios and multi-gw issues
March, 2006
IETF 65th – autoconf WG
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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
S.Ruffino - Autoconf scenarios and multi-gw issues
March, 2006
IETF 65th – autoconf WG
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Routing dependance from address choice
2001:db8:0:a::/64
2001:db8:0:b::/64
2001:db8:0:a::1/64
•
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
2001:db8:0:a::1/64
• Low throughput, high latency and delay variation
S.Ruffino - Autoconf scenarios and multi-gw issues
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Routing dependance from address choice
(cont.)
Lower throughput due to
sub optimal downlink path
S.Ruffino - Autoconf scenarios and multi-gw issues
March, 2006
IETF 65th – autoconf WG
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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.
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Next steps
• Revise and enhance draft-ruffino-autoconfconn-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 !
S.Ruffino - Autoconf scenarios and multi-gw issues
March, 2006
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