It can work with BiDi modules, I have a pair here that work fine in the 2100. They were the cheapest BiDi pair I could find!
When connected it looks like:
[24.03-RELEASE][root@2100-2.stevew.lan]/root: ifconfig -vvvm mvneta0
mvneta0: flags=1008a43<UP,BROADCAST,RUNNING,ALLMULTI,SIMPLEX,MULTICAST,LOWER_UP> metric 0 mtu 1500
description: WAN
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
inet 172.21.16.220 netmask 0xffffff00 broadcast 172.21.16.255
inet6 fe80::2e0:edff:feb6:1359%mvneta0 prefixlen 64 scopeid 0x1
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>
drivername: mvneta0
It looks like the module you have is rated as dual speed but the 2100 can only run at 1G. Any chance the ISP is set at 100Mbps?