Ola pessoal, meu caso eh o seguinte: depois que atualizei meu Ubuntuo do 10.10 para o 11.04 (instalacao limpa) a conexao de internet com a placa de rede wireless Broadcom BCM4312 cai direto.... mesmo usando um driver antigo ou o driver proprietario, Broadcom STA, o problema persiste.
Segue os resultados dos comandos:
iwconfig
lo no wireless extensions.
eth0 no wireless extensions.
eth1 IEEE 802.11bg ESSID:"IADBP"
Mode:Managed Frequency:2.437 GHz Access Point: Not-Associated
Bit Rate:54 Mb/s Tx-Power:24 dBm
Retry min limit:7 RTS thr:off Fragment thr:off
Power Managementmode:All packets received
Link Quality=5/5 Signal level=0 dBm Noise level=-57 dBm
Rx invalid nwid:0 Rx invalid crypt:0 Rx invalid frag:0
Tx excessive retries:0 Invalid misc:0 Missed beacon:0
lspci
00:00.0 Host bridge: ATI Technologies Inc RS690 Host Bridge
00:01.0 PCI bridge: ATI Technologies Inc RS690 PCI to PCI Bridge (Internal gfx)
00:06.0 PCI bridge: ATI Technologies Inc RS690 PCI to PCI Bridge (PCI Express Port 2)
00:07.0 PCI bridge: ATI Technologies Inc RS690 PCI to PCI Bridge (PCI Express Port 3)
00:12.0 SATA controller: ATI Technologies Inc SB600 Non-Raid-5 SATA
00:13.0 USB Controller: ATI Technologies Inc SB600 USB (OHCI0)
00:13.1 USB Controller: ATI Technologies Inc SB600 USB (OHCI1)
00:13.4 USB Controller: ATI Technologies Inc SB600 USB (OHCI4)
00:13.5 USB Controller: ATI Technologies Inc SB600 USB Controller (EHCI)
00:14.0 SMBus: ATI Technologies Inc SBx00 SMBus Controller (rev 14)
00:14.1 IDE interface: ATI Technologies Inc SB600 IDE
00:14.2 Audio device: ATI Technologies Inc SBx00 Azalia (Intel HDA)
00:14.3 ISA bridge: ATI Technologies Inc SB600 PCI to LPC Bridge
00:14.4 PCI bridge: ATI Technologies Inc SBx00 PCI to PCI Bridge
00:18.0 Host bridge: Advanced Micro Devices [AMD] K8 [Athlon64/Opteron] HyperTransport Technology Configuration
00:18.1 Host bridge: Advanced Micro Devices [AMD] K8 [Athlon64/Opteron] Address Map
00:18.2 Host bridge: Advanced Micro Devices [AMD] K8 [Athlon64/Opteron] DRAM Controller
00:18.3 Host bridge: Advanced Micro Devices [AMD] K8 [Athlon64/Opteron] Miscellaneous Control
01:05.0 VGA compatible controller: ATI Technologies Inc RS690M [Radeon X1200 Series]
02:00.0 Network controller: Broadcom Corporation BCM4312 802.11b/g LP-PHY (rev 01)
05:00.0 Ethernet controller: Atheros Communications AR8132 Fast Ethernet (rev c0)
Ja fuçei em quase todos os tutos e foruns que existem, mas o problema persiste..... alguem poderia me ajuda?

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Obrigado galera!!!