rtnetlink routes — the RTM_*ROUTE messages.

list/1 reads routes; add/5, add_default/3, replace/5, delete/5 and delete_default/3 install, update, and remove them. IPv4 and IPv6 are both supported — the address family is detected from the destination and gateway, which must agree.

Address-typed fields (:dst, :gateway) on a decoded %Route{} are Linx.IP structs; verbs accept strings or Linx.IPs.

Options

add/5, replace/5, delete/5 (and their *_default forms) take an options keyword:

• :table — routing table (1..2^32-1). Default 254 (the main table).
• :protocol — the route's origin tag (rtm_protocol). An integer 0..255, or one of :kernel (2), :boot (3, the default), :static (4), :ra (9), :dhcp (16). This is the ownership marker a reconciler uses to manage only its own routes (see the reconcile design notes).
• :metric — the route metric / RTA_PRIORITY (a u32); omitted when not given, which the kernel treats as metric 0.

add vs replace

• add/5 uses NLM_F_CREATE | NLM_F_EXCL — it errors (:eexist) if a matching route already exists.

• replace/5 uses NLM_F_CREATE | NLM_F_REPLACE — create-or-replace. It installs the route if absent and overwrites it (e.g. a changed gateway) if present. This is the idempotent upsert a reconciler applies, and the only way to change a route's mutable attributes in place.

The two table representations

struct rtmsg's table is a u8, so tables above 255 are conveyed via the separate RTA_TABLE attribute (mapped to :table_ext); the kernel sets the header byte to RT_TABLE_UNSPEC in that case. target_table/1 returns the effective table — taking :table_ext when present, falling back to :table.

Example

{:ok, sock} = Rtnl.open()

:ok = Route.add_default(sock, "10.0.0.1")
:ok = Route.add(sock, "192.168.9.0", 24, "10.0.0.254")

# Change the gateway in place (idempotent upsert):
:ok = Route.replace(sock, "192.168.9.0", 24, "10.0.0.253")

# A route in a custom table, tagged with a dedicated protocol:
:ok = Route.add(sock, "10.50.0.0", 24, "10.0.0.1", table: 100, protocol: 4)

{:ok, routes} = Route.list(sock)
{:ok, route} = Route.get(sock, "192.168.9.7")

:ok = Route.delete_default(sock, "10.0.0.1")

The wire format — struct rtmsg and the RTA_* attributes (include/uapi/linux/rtnetlink.h) — is declared with the Linx.Netlink.Codec DSL.