modify Ethernet FSC in Scapy

Question

I need to send malformed Ethernet frames for testing purposes. I have disabled offload for Rx and Tx checksums:

root@T60:~# ethtool --show-offload eth0
Features for eth0:
rx-checksumming: off
tx-checksumming: off
    tx-checksum-ipv4: off [fixed]
    tx-checksum-unneeded: off [fixed]
    tx-checksum-ip-generic: off
    tx-checksum-ipv6: off [fixed]
    tx-checksum-fcoe-crc: off [fixed]
    tx-checksum-sctp: off [fixed]

However, does this offloading involve only IP, TCP and UDP checksums? Is it possible to send frames with malformed Frame Sequence Check in Ethernet footer using Scapy? I highly doubt in this as calculating the Ethernet FSC is probably implemented in NIC hardware?

http://stackoverflow.com/questions/6329583/how-to-reliably-generate-ethernet-frame-errors-in-software — RyPeck, Oct 13 '13 at 20:41
@RyPeck I tried this python script before posting this question and at least on my Intel 82573L(e1000e module) it's not sending out frames with modified FSC. If I send those frames to Cisco switch I can verify this with "FCS errors" counter in "sh controllers" output and if I send those frames to another machine(Broadcom BCM5721 NIC), then there are no errors in "ip -s link" output. Last but not least, I would prefer to pull this off using Scapy. — Martin, Oct 13 '13 at 23:06

score 1 · Accepted Answer · answered Oct 19 '13 at 05:13

1

YES , the NIC offover just off ether, IP, TCP, UDP 's checksum, and UDP checksum is checked seldom.
YES, SCAPY can assembly packet even it's bad checksum by using raw socket
just try la :)

answered Oct 19 '13 at 05:13

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modify Ethernet FSC in Scapy

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