Is there a SW based checksum fix for UDP header on inner UDP header of a VxLAN packet

[gavi.teit...@gmail.com]

Hi,

I'm looking to generate VxLAN packets via the stateless python API, and am unable to generate packets with a varied inner packet UDP header that has a valid checksum, since the only vm instruction class I could find which provides a fix to the UDP checksum is the STLVmFixChecksumHw class, however, my HW does not support fixing the inner packet's checksum.

As I cannot use the STLVmFixChecksumHw class to fix the checksum, I'm looking for an alternate. Is there a SW based UDP checksum fixer class?
If not, how can I manipulate the STL VM framework so that I can calculate it manually and update it?

Here is my code for the VM:

vm = STLScVmRaw([
STLVmFlowVar(name="inner_udp_src_port",
min_value=self.innerUdpSrcPortRangeLow,
max_value=self.innerUdpSrcPortRangeHigh,
size=2, op="inc"),
STLVmWrFlowVar(fv_name="inner_udp_src_port",
pkt_offset="UDP:1.sport"),
STLVmFixChecksumHw(l3_offset="IP:1",
l4_offset="UDP:1",
l4_type=CTRexVmInsFixHwCs.L4_TYPE_UDP),

STLVmFlowVar(name="vxlan_entropy_src_port",
min_value=self.outerUdpSrcPortRangeLow,
max_value=self.outerUdpSrcPortRangeHigh,
size=2, op="inc"),
STLVmWrFlowVar(fv_name="vxlan_entropy_src_port",
pkt_offset="UDP.sport"),
STLVmFixChecksumHw(l3_offset="IP",
l4_offset="UDP",
l4_type=CTRexVmInsFixHwCs.L4_TYPE_UDP),
])

Note, that the checksum is properly fixed for the outer packet, but not for the inner packet, as my HW does not support a fix checksum offload for the inner packet.

During the Trex run, I get the following warning:

"WARNING: No IP underlayer to compute checksum. Leaving null."

Here is a tcpdump sampling of a packet generated:

tcpdump: listening on ens1f0, link-type EN10MB (Ethernet), capture size 262144 bytes
16:41:55.214958 24:8a:07:ad:7a:fa > 50:6b:4b:d5:57:fe, ethertype IPv4 (0x0800), length 196: (tos 0x0, ttl 64, id 1, offset 0, flags [none], proto UDP (17), length 182)
70.70.70.6.1025 > 70.70.70.5.4789: [udp sum ok] VXLAN, flags [I] (0x08), vni 0
e4:11:22:06:00:00 > e4:11:22:05:00:00, ethertype IPv4 (0x0800), length 146: (tos 0x0, ttl 64, id 1, offset 0, flags [none], proto UDP (17), length 132, bad cksum 0 (->6d5b)!)
1.1.6.6.1052 > 1.1.5.6.1025: [bad udp cksum 0x0d8f -> 0xf2b8!] UDP, length 104
0x0000: 506b 4bd5 57fe 248a 07ad 7afa 0800 4500
0x0010: 00b6 0001 0000 4011 619f 4646 4606 4646
0x0020: 4605 0401 12b5 00a2 1342 0800 0000 0000
0x0030: 0000 e411 2205 0000 e411 2206 0000 0800
0x0040: 4500 0084 0001 0000 4011 0000 0101 0606
0x0050: 0101 0506 041c 0401 0070 0d8f 6162 6364
0x0060: 6566 6768 696a 6b6c 6d6e 6f70 7172 7374
0x0070: 7576 7778 797a 4142 4344 4546 4748 494a
0x0080: 4b4c 4d4e 4f50 5152 5354 5556 5758 595a
0x0090: 6162 6364 6566 6768 696a 6b6c 6d6e 6f70
0x00a0: 7172 7374 7576 7778 797a 4142 4344 4546
0x00b0: 4748 494a 4b4c 4d4e 4f50 5152 5354 5556
0x00c0: 5758 595a
1 packet captured
1 packet received by filter
0 packets dropped by kernel

[hanoh haim]

Hi gavi,

For the inner ip/udp use the sw instruction to fix ip checksum and set udp.cs to be zero.

Hanoh

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Hanoh

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