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87 lines
3.0 KiB
Markdown
87 lines
3.0 KiB
Markdown
# Auto-configuration for nested subnets on a tree topology
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This example demonstrates IPv6 subnet auto-configuration for networks on
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a tree topology.
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This allows to connect multiple links with individual subnets and route
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between them.
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Each link can have an arbitrary number of hosts and routers.
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Routers can have multiple interfaces to connect different downlinks.
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If you can ensure there is only a single router on each link, you can
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skip the coordination protocol and save some resources by enabling
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the `gnrc_ipv6_auto_subnets_simple` module.
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Routers can still have multiple downstream interfaces but there can be
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only a single router in each subnet.
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## Setup on native
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To simulate such a network on `native` a `setup_taps.sh` script is provided that
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will create TAP interfaces and bridges.
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Each bridge will be it's own subnet and `native` instances will act as routers
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to route between them.
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The setup script will also start `radvd` to advertise a large prefix that allows
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for sub-division by RIOT.
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The interfaces that should be created are specified in the `tapology.txt` file.
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Each router will have (at least) two interfaces that should be on different
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bridges.
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To start the first router, run
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make term PORT="tap_a0 tap_b1"
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This will route between the `tap_a0` interface on `br0` and the `tap_b1`
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interface on `br1`.
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Start more `native` instances to simulate a cascading tree network:
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make term PORT="tap_b0 tap_c1"
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make term PORT="tap_c0 tap_d1"
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…
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It is also possible to connect non-routing leaf nodes with a single interface:
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make flash term LEAF=1 PORT=tap_b2
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## Setup on hardware
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On physical hardware the setup will be the same.
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Routing nodes need at least two interfaces between which they can route.
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For a simple setup, you can use `ethos` or `slipdev` to turn any UART into
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a network interface. (If you need to use DHCPv6 IA_PD for obtaining a prefix,
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use `slipdev_l2addr` instead of plain `slipdev`)
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### Obtaining the prefix
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#### Via router advertisements
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Usually routers are configured to advertise a /64 prefix that can not be divided
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further when using SLAAC.
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If you can configure your router to advertise a larger prefix instead, this
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will be the easiest solution.
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#### Via DHCPv6
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If you can't change the configuration of your router, but your router supports
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DHCPv6 IA_PD, you can use this to request a larger prefix.
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This requires a gateway node that uses the `gnrc_dhcpv6_client_simple_pd`
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module *instead* of `gnrc_ipv6_auto_subnets`.
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Make sure to set the `CONFIG_GNRC_DHCPV6_CLIENT_6LBR_UPSTREAM` option to the
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ID of the upstream interface on the gateway device, e.g.
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CFLAGS += -DCONFIG_GNRC_DHCPV6_CLIENT_6LBR_UPSTREAM=6
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As with GNRC the interface ID is based on the PID of the interface thread, this can
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change if you add modules / threads and is a common source of errors.
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If the configuration is set wrong, you will not get a prefix for the downstream
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interface(s).
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