I wrote:

> BTW, does anyone see the similar hardware ip4csum-tx problem
> with short IP packets on ex(4)?
 :
> ex0 at pci1 dev 4 function 0: 3Com 3c980C-TXM 10/100 Ethernet (rev. 0x78)

More info:

Note this only happens on ping -s 1473 or 1474
(i.e. 1 or 2 byte octets with IP headers).

My 3C905B-TX on i386 running 4.99.3 also has the problem:
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ex0 at pci0 dev 5 function 0: 3Com 3c905B-TX 10/100 Ethernet (rev. 0x30)
---

But there is a report that the follwoing 3C905C-TX on alpha
running 3.1_RC1 doesn't:
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ex0 at pci0 dev 5 function 0: 3Com 3c905C-TX 10/100 Ethernet with mngmt (rev. 0x74)
---
Izumi Tsutsui