> You may want to take a look at PR-13770 (too).  I experienced the same
> "transmit FIFO underrun" with the sip0 driver on a freshly installed NetBSD
> 1.6.1 system, and found that the fix described in PR-13770 worked.

Spot on.
Thanks for that Dion.

I now get 

Mar  1 20:43:41 artworks /netbsd: sip0: frame alignment error
Mar  1 20:43:43 artworks /netbsd: sip0: frame alignment error

but only a few so far and at least the error rate is well down

Name  Mtu   Network       Address              Ipkts Ierrs    Opkts Oerrs Colls
sip0  1500  <Link>        00:09:5b:60:7e:3e    92303     2    73643     2 64702
sip0  1500  1.2.3.4/      1.2.3.6      
                          224.0.0.1            92303     2    73643     2 64702
sip0  1500  1.2.3.4/      1.2.3.9              92303     2    73643     2 64702
sip0  1500  1.2.3.4/      1.2.3.10             92303     2    73643     2 64702


I submitted a new PR.

Thanks,
James
---
James Burton (james@jmsh.net)           Call the men of science, let them
                                        hear this song. Tell them Albert
                                        Einstein & Copernicus were wrong.