linux – 如何接收错误的以太网帧并禁用CRC / FCS计算？

它可能在您的内核,NIC和驱动程序以及ethtool版本上.

我们需要告诉驱动程序/硬件做两件通常不会做的事情：
1)将FCS字段传递到网络堆栈. (通常这会在被传递之前被截断)
2)不丢弃具有错误FCS字段的数据包,而是按原样传递它们

有两种ethtool选项可以实现以下各项：

ethtool -K eth0 rx-fcs on  #1 above: give us the FCS field
ethtool -K eth0 rx-all on  #2 above: even receive bad packets

有了这些,我可以使用wireshark或tcpdump来查看FCS字段,即使它们不正确. (在我的情况下,我有一些网络设备,它使用准确的时间戳即时替换校验和 – 这会导致数据包显示为“坏”,并使用上述内容进行恢复)

并非所有卡都会实现这一点！他们可能将上述ethtool选项“修复”或不回应.

以1G的速度,我看到e1000卡运行良好.在10G我还没有找到一个可以做到这一点的网卡,而且必须依赖更复杂的数据采集卡.

同样,我不知道最低内核/ ethtool版本要求是什么,但我确实记得要升级CentOS服务器以使其工作.

我也知道r8169和e1000驱动程序/卡可以做到,但根本不能说任何其他组合.

另请注意,您将无法在发送它们的计算机上捕获传出的FCS值,因为它们在过程中很晚才添加(可能已卸载到卡本身),因此pcap无法看到.

在Linux 3.10.11内核上,使用ethtool 3.10：

$ethtool -k eth0
Features for eth0:
rx-checksumming: on
tx-checksumming: on
    tx-checksum-ipv4: off [fixed]
    tx-checksum-ip-generic: on
    tx-checksum-ipv6: off [fixed]
    tx-checksum-fcoe-crc: off [fixed]
    tx-checksum-sctp: off [fixed]
scatter-gather: on
    tx-scatter-gather: on
    tx-scatter-gather-fraglist: off [fixed]
tcp-segmentation-offload: on
    tx-tcp-segmentation: on
    tx-tcp-ecn-segmentation: off [fixed]
    tx-tcp6-segmentation: on
udp-fragmentation-offload: off [fixed]
generic-segmentation-offload: on
generic-receive-offload: on
large-receive-offload: off [fixed]
rx-vlan-offload: on
tx-vlan-offload: on
ntuple-filters: off [fixed]
receive-hashing: on
highdma: on [fixed]
rx-vlan-filter: on [fixed]
vlan-challenged: off [fixed]
tx-lockless: off [fixed]
netns-local: off [fixed]
tx-gso-robust: off [fixed]
tx-fcoe-segmentation: off [fixed]
tx-gre-segmentation: off [fixed]
tx-udp_tnl-segmentation: off [fixed]
fcoe-mtu: off [fixed]
tx-nocache-copy: on
loopback: off [fixed]
rx-fcs: off
rx-all: off
tx-vlan-stag-hw-insert: off [fixed]
rx-vlan-stag-hw-parse: off [fixed]
rx-vlan-stag-filter: off [fixed]

然后：

$sudo ethtool -K eth0 rx-fcs on rx-all on

给我：

$ethtool -k eth0
Features for eth0:
rx-checksumming: on
tx-checksumming: on
    tx-checksum-ipv4: off [fixed]
    tx-checksum-ip-generic: on
    tx-checksum-ipv6: off [fixed]
    tx-checksum-fcoe-crc: off [fixed]
    tx-checksum-sctp: off [fixed]
scatter-gather: on
    tx-scatter-gather: on
    tx-scatter-gather-fraglist: off [fixed]
tcp-segmentation-offload: on
    tx-tcp-segmentation: on
    tx-tcp-ecn-segmentation: off [fixed]
    tx-tcp6-segmentation: on
udp-fragmentation-offload: off [fixed]
generic-segmentation-offload: on
generic-receive-offload: on
large-receive-offload: off [fixed]
rx-vlan-offload: on
tx-vlan-offload: on
ntuple-filters: off [fixed]
receive-hashing: on
highdma: on [fixed]
rx-vlan-filter: on [fixed]
vlan-challenged: off [fixed]
tx-lockless: off [fixed]
netns-local: off [fixed]
tx-gso-robust: off [fixed]
tx-fcoe-segmentation: off [fixed]
tx-gre-segmentation: off [fixed]
tx-udp_tnl-segmentation: off [fixed]
fcoe-mtu: off [fixed]
tx-nocache-copy: on
loopback: off [fixed]
rx-fcs: on
rx-all: on
tx-vlan-stag-hw-insert: off [fixed]
rx-vlan-stag-hw-parse: off [fixed]
rx-vlan-stag-filter: off [fixed]