[Arista][Ipfwd][202012] Unexpected behavior when forwarding 0xffff IP checksum packets on 7050CX3 Arista devices

[xwjiang-ms]

Description

0xffff is invalid IP checksum, if DUT receive 0xffff checksum packet, we expect 2 kind of results:

1. 0xffff checksum is invalid, dut will drop this packet
2. 0xffff checksum is invalid, dut will forward this packet, and will reduce TTL and change IP checksum, because IP checksum is calculated by IP headers include TTL

But on 7050CX3 with 202012 image, the behavior is unexpected.
Similar issue found in 720DT-48S, and was fixed in #13088

We have test script in sonic-mgmt:
Test script: https://github.com/sonic-net/sonic-mgmt/blob/master/tests/ip/test_ip_packet.py
Test case: test_forward_ip_packet_with_0xffff_chksum_tolerant and test_forward_ip_packet_with_0xffff_chksum_drop

Steps to reproduce the issue:

1. Create IP packet with 0xffff checksum
2. Forward this IP packet to 7050CX3 Arista devices with 202012 image
3. Use portstat and ptf to check packets forwarded by 7050CX3 Arista devices

Describe the results you received:

Dut could forward 0xffff checksum, TTL-1, but IP checksum doesn't change

Describe the results you expected:

In other versions of images, 7050CX3's behavior is result 2, so I think in 202012 image, 7050CX3 should forward this packet and change checksum.

Output of show version:

SONiC Software Version: SONiC.20201231.86
Distribution: Debian 10.13
Kernel: 4.19.0-12-2-amd64
Build commit: 6d9ae9bcc8
Build date: Sat Jan  7 06:47:40 UTC 2023
Built by: cloudtest@ef909824c000000 Platform: x86_64-arista_7050cx3_32s
HwSKU: Arista-7050CX3-32S-C32
ASIC: broadcom
ASIC Count: 1
Serial Number: JPE21101722
Uptime: 17:27:27 up  1:04,  1 user,  load average: 0.52, 0.49, 0.61 Docker images:
REPOSITORY                 TAG                 IMAGE ID            SIZE
docker-mux                 20201231.86         7349977751f1        415MB
docker-mux                 latest              7349977751f1        415MB
docker-sonic-restapi       20201231.86         c949e32b51d2        382MB
docker-sonic-restapi       latest              c949e32b51d2        382MB
docker-sonic-telemetry     20201231.86         3b0e7281709a        452MB
docker-sonic-telemetry     latest              3b0e7281709a        452MB
docker-orchagent           20201231.86         660b15076805        391MB
docker-orchagent           latest              660b15076805        391MB
docker-teamd               20201231.86         3b9f7b9fd2d7        374MB
docker-teamd               latest              3b9f7b9fd2d7        374MB
docker-fpm-frr             20201231.86         0e25fb80657b        392MB
docker-fpm-frr             latest              0e25fb80657b        392MB
docker-acms                20201231.86         8edb557b4fe2        465MB
docker-acms                latest              8edb557b4fe2        465MB
docker-platform-monitor    20201231.86         a7087a94ca73        545MB
docker-platform-monitor    latest              a7087a94ca73        545MB
docker-syncd-brcm          20201231.86         f3af2aeb0b40        655MB
docker-syncd-brcm          latest              f3af2aeb0b40        655MB
docker-database            20201231.86         48f82f28a8bb        362MB
docker-database            latest              48f82f28a8bb        362MB
docker-router-advertiser   20201231.86         981f7e6f4ae4        362MB
docker-router-advertiser   latest              981f7e6f4ae4        362MB
docker-snmp                20201231.86         6a2fde9ee8d9        405MB
docker-snmp                latest              6a2fde9ee8d9        405MB
docker-lldp                20201231.86         82d443715a59        402MB
docker-lldp                latest              82d443715a59        402MB
docker-dhcp-relay          20201231.86         65c306c84817        378MB
docker-dhcp-relay          latest              65c306c84817        378MB
k8s.gcr.io/pause           3.5                 ed210e3e4a5b        683kB

Output of show techsupport:

(paste your output here or download and attach the file here )

Additional information you deem important (e.g. issue happens only occasionally):

[neethajohn]

@theasianpianist, can you check what is the expected behavior on this platform?

[theasianpianist]

Issue did not auto-close for some reason. Fixed by #13431