In the 2100 the SFP combo port has very limited configuration. It will appear as a 1000baseSX link whatever is connected to it:
[admin@2100-2.stevew.lan]/root: ifconfig -vvm mvneta0
mvneta0: flags=8a43<UP,BROADCAST,RUNNING,ALLMULTI,SIMPLEX,MULTICAST> metric 0 mtu 1500
options=800bb<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING,JUMBO_MTU,VLAN_HWCSUM,LINKSTATE>
capabilities=804bb<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING,JUMBO_MTU,VLAN_HWCSUM,LRO,LINKSTATE>
ether 00:e0:ed:b6:13:59
inet6 fe80::2e0:edff:feb6:1359%mvneta0 prefixlen 64 scopeid 0x1
inet 172.21.16.220 netmask 0xffffff00 broadcast 172.21.16.255
media: Ethernet autoselect (1000baseSX <full-duplex>)
status: active
supported media:
media autoselect
media 1000baseSX mediaopt full-duplex
media 1000baseSX
media 1000baseT mediaopt full-duplex,master
media 1000baseT mediaopt full-duplex
media 1000baseT mediaopt master
media 1000baseT
media 100baseTX mediaopt full-duplex
media 100baseTX
media 10baseT/UTP mediaopt full-duplex
media 10baseT/UTP
media none
nd6 options=23<PERFORMNUD,ACCEPT_RTADV,AUTO_LINKLOCAL>
So it will either work or not with no real options tweak if it doesn't.
Steve