Getting all ipv4 and ipv6 packet and byte counts on a router

I'm running 14.3 on my gateway router and I want to answer a simple question: How much
ipv4 vs ipv6 traffic is entering and leaving the network via the external interface?

And by traffic I mean packets *and* bytes destined for the gateway router *and* for
traffic forwarded via the router in both directions.

I looked at netstat(1) which pointed to netinet6/ip6_var.h and from that I deduce that
link-level stats do not discriminate between v4/v6 and address-level stats only count
traffic associated with a router address (I also double checked this by scanning for
xo_emit() with "bytes" - no joy).

I don't read kernel well enough to check, but are v4/v6 packet&bytes counted separately on
an interface basis? If so, how do I get at them in user space?

If not, do I need to write some bpf/pcap code to do the counting myself? This deployment
happens to have CPU to burn so it's feasible, but it seems like a common requirement so
sending packets into user-space just to collect these stats seems surprising. In any
event, if someone can hit me over the head with a clue bat I'd appreciate it.


Mark.