rt_t
#define IRB2RT(irb) (rt_t *)((caddr_t)(irb) - offsetof(rt_t, rt_irb))
irb_refhold(&((rt_t *)(rn))->rt_irb);
irb_refrele_ftable(&((rt_t *)(rn))->rt_irb);
DTRACE_PROBE1(irb__free, rt_t *, rt);