dev/em: Link is not up until 2 seconds after "ifconfig up"

My experimental 1U box which has em0 and em1 shows following result.
Doing "ifconfig em1 up" after "ifconfig em1 down", link is down 1 or
more seconds.  I'm trying to make this box as VRRP router, so 1
second down during master/backup transition (which uses down, mac
address setting, and up) causes ping-pong transition of master router.

I think I can work around some timeout tweaks in VRRP daemon side, but
I hope em(4) driver (or hardware problem?) can deal with it.  I did
same test with fxp(4) and rl(4), but these interfaces are active after
"ifconfig up" immediately.


# ifconfig em1 down; ifconfig em1 up; ifconfig em1; sleep 1; ifconfig em1; sleep 1; ifconfig em1
em1: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
        options=3<RXCSUM,TXCSUM>
        inet 192.168.128.3 netmask 0xffffff00 broadcast 192.168.128.255
        inet6 fe80::230:48ff:fe28:4d75%em1 prefixlen 64 scopeid 0x2 
        ether 00:30:48:28:4d:75
        media: Ethernet autoselect
        status: no carrier
em1: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
        options=3<RXCSUM,TXCSUM>
        inet 192.168.128.3 netmask 0xffffff00 broadcast 192.168.128.255
        inet6 fe80::230:48ff:fe28:4d75%em1 prefixlen 64 scopeid 0x2 
        ether 00:30:48:28:4d:75
        media: Ethernet autoselect
        status: no carrier
em1: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
        options=3<RXCSUM,TXCSUM>
        inet 192.168.128.3 netmask 0xffffff00 broadcast 192.168.128.255
        inet6 fe80::230:48ff:fe28:4d75%em1 prefixlen 64 scopeid 0x2 
        ether 00:30:48:28:4d:75
        media: Ethernet autoselect (100baseTX <full-duplex>)
        status: active

# pciconf -lv
...
em0_at_pci2:3:0:   class=0x020000 card=0x10118086 chip=0x10108086 rev=0x01 hdr=0x00
    vendor   = 'Intel Corporation'
    device   = '82546EB Gigabit Ethernet Controller (copper)'
    class    = network
    subclass = ethernet
em1_at_pci2:3:1:   class=0x020000 card=0x10118086 chip=0x10108086 rev=0x01 hdr=0x00
    vendor   = 'Intel Corporation'
    device   = '82546EB Gigabit Ethernet Controller (copper)'
    class    = network
    subclass = ethernet
...


-- 
Jun Kuriyama <kuriyama_at_imgsrc.co.jp> // IMG SRC, Inc.
             <kuriyama_at_FreeBSD.org> // FreeBSD Project