无法设置 1 Gbit 以太网连接

Question

我使用的是 Kubuntu 12.10。我的路由器与我的另一台 PC 以 1Gbit 连接运行，我有 1Gbit 以太网卡，电缆是 cat5e，无法设置 1Gbit 以太网连接。只有 100Mbit/s。

lspci|grep 以太网

04:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168B PCI Express Gigabit Ethernet controller (rev 01)

sudo ethtool eth0

Settings for eth0:
    Supported ports: [ TP ]
    Supported link modes:   10baseT/Half 10baseT/Full 
                            100baseT/Half 100baseT/Full 
                            1000baseT/Full 
    Supported pause frame use: No
    Supports auto-negotiation: Yes
    Advertised link modes:  10baseT/Half 10baseT/Full 
                            100baseT/Half 100baseT/Full 
                            1000baseT/Full 
    Advertised pause frame use: Symmetric Receive-only
    Advertised auto-negotiation: Yes
    Speed: 100Mb/s
    Duplex: Full
    Port: Twisted Pair
    PHYAD: 0
    Transceiver: internal
    Auto-negotiation: on
    MDI-X: Unknown
    Supports Wake-on: pumbg
    Wake-on: g
    Current message level: 0x00000033 (51)
                           drv probe ifdown ifup
    Link detected: yes

以太网卡的内核模块是 r8168。出了什么问题？