Preface:

I was having trouble setting up my Celestica Seastone DX010 100GBE switch to breakout a single 100gbe port into 25gbe due to an bug in Sonic NOS. Using this reddit guide was a bit confusing but after hours of troubleshooting, it seemed to work.

Procedure

Edit config file with following command:

sudo vi /etc/sonic/config_db.json

Add in Ethernet 1-3 and make sure speed is set to "25000" for 25gbe, split out the lanes from 65,66,67,68 into Eth0-3, set "admin_status" to "up" on Eth0-4, set aliases on all 4 -- I did "Eth1/1-4", and set "fec" to "none". After that, run below command to reload config:

sudo config reload -y

My Config(for reference purposes):

{
    "DEVICE_METADATA": {
        "localhost": {
            "hwsku": "Seastone-DX010",
            "platform": "x86_64-cel_seastone-r0",
            "mac": "00:e0:dc:ac:7e:9d",
            "hostname": "sonic",
            "type": "LeafRouter",
            "bgp_asn": "65100"
        }
    },
    "PORT": {
        "Ethernet0": {
            "alias": "Eth1/1",
            "fec": "none",
            "lanes": "65",
            "speed": "25000",
            "index": "1",
            "autoneg": "1",
            "admin_status": "up",
            "mtu": "9100"
        },
        "Ethernet1": {
            "alias": "Eth1/2",
            "fec": "none",
            "lanes": "66",
            "speed": "25000",
            "index": "1",
            "autoneg": "1",
            "admin_status": "up",
            "mtu": "9100"
        },
        "Ethernet2": {
            "alias": "Eth1/3",
            "fec": "none",
            "lanes": "67",
            "speed": "25000",
            "index": "1",
            "autoneg": "1",
            "admin_status": "up",
            "mtu": "9100"
        },
        "Ethernet3": {
            "alias": "Eth1/4",
            "fec": "none",
            "lanes": "68",
            "speed": "25000",
            "index": "1",
            "autoneg": "1",
            "admin_status": "up",
            "mtu": "9100"
        },
        "Ethernet4": {
            "alias": "Eth2",
            "lanes": "69,70,71,72",
            "speed": "100000",
            "index": "2",
            "admin_status": "up",
            "mtu": "9100"
        },
        "Ethernet8": {
            "alias": "Eth3",
            "lanes": "73,74,75,76",
            "speed": "100000",
            "index": "3",
            "admin_status": "up",
            "mtu": "9100"
        },
        "Ethernet12": {
            "alias": "Eth4",
            "lanes": "77,78,79,80",
            "speed": "100000",
            "index": "4",
            "admin_status": "up",
            "mtu": "9100"
        },
        "Ethernet16": {
            "alias": "Eth5",
            "lanes": "33,34,35,36",
            "speed": "100000",
            "index": "5",
            "admin_status": "up",
            "mtu": "9100"
        },
        "Ethernet20": {
            "alias": "Eth6",
            "lanes": "37,38,39,40",
            "speed": "100000",
            "index": "6",
            "admin_status": "up",
            "mtu": "9100"
        },
        "Ethernet24": {
            "alias": "Eth7",
            "lanes": "41,42,43,44",
            "speed": "100000",
            "index": "7",
            "admin_status": "up",
            "mtu": "9100"
        },
        "Ethernet28": {
            "alias": "Eth8",
            "lanes": "45,46,47,48",
            "speed": "100000",
            "index": "8",
            "admin_status": "up",
            "mtu": "9100"
        },
        "Ethernet32": {
            "alias": "Eth9",
            "lanes": "49,50,51,52",
            "speed": "100000",
            "index": "9",
            "admin_status": "up",
            "mtu": "9100"
        },
        "Ethernet36": {
            "alias": "Eth10",
            "lanes": "53,54,55,56",
            "speed": "100000",
            "index": "10",
            "admin_status": "up",
            "mtu": "9100"
        },
        "Ethernet40": {
            "alias": "Eth11",
            "lanes": "57,58,59,60",
            "speed": "100000",
            "index": "11",
            "admin_status": "up",
            "mtu": "9100"
        },
        "Ethernet44": {
            "alias": "Eth12",
            "lanes": "61,62,63,64",
            "speed": "100000",
            "index": "12",
            "admin_status": "up",
            "mtu": "9100"
        },
        "Ethernet48": {
            "alias": "Eth13",
            "lanes": "81,82,83,84",
            "speed": "100000",
            "index": "13",
            "admin_status": "up",
            "mtu": "9100"
        },
        "Ethernet52": {
            "alias": "Eth14",
            "lanes": "85,86,87,88",
            "speed": "100000",
            "index": "14",
            "admin_status": "up",
            "mtu": "9100"
        },
        "Ethernet56": {
            "alias": "Eth15",
            "lanes": "89,90,91,92",
            "speed": "100000",
            "index": "15",
            "admin_status": "up",
            "mtu": "9100"
        },
        "Ethernet60": {
            "alias": "Eth16",
            "lanes": "93,94,95,96",
            "speed": "100000",
            "index": "16",
            "admin_status": "up",
            "mtu": "9100"
        },
        "Ethernet64": {
            "alias": "Eth17",
            "lanes": "97,98,99,100",
            "speed": "100000",
            "index": "17",
            "admin_status": "up",
            "mtu": "9100"
        },
        "Ethernet68": {
            "alias": "Eth18",
            "lanes": "101,102,103,104",
            "speed": "100000",
            "index": "18",
            "admin_status": "up",
            "mtu": "9100"
        },
        "Ethernet72": {
            "alias": "Eth19",
            "lanes": "105,106,107,108",
            "speed": "100000",
            "index": "19",
            "admin_status": "up",
            "mtu": "9100"
        },
        "Ethernet76": {
            "alias": "Eth20",
            "lanes": "109,110,111,112",
            "speed": "100000",
            "index": "20",
            "admin_status": "up",
            "mtu": "9100"
        },
        "Ethernet80": {
            "alias": "Eth21",
            "lanes": "1,2,3,4",
            "speed": "100000",
            "index": "21",
            "admin_status": "up",
            "mtu": "9100"
        },
        "Ethernet84": {
            "alias": "Eth22",
            "lanes": "5,6,7,8",
            "speed": "100000",
            "index": "22",
            "admin_status": "up",
            "mtu": "9100"
        },
        "Ethernet88": {
            "alias": "Eth23",
            "lanes": "9,10,11,12",
            "speed": "100000",
            "index": "23",
            "admin_status": "up",
            "mtu": "9100"
        },
        "Ethernet92": {
            "alias": "Eth24",
            "lanes": "13,14,15,16",
            "speed": "100000",
            "index": "24",
            "admin_status": "up",
            "mtu": "9100"
        },
        "Ethernet96": {
            "alias": "Eth25",
            "lanes": "17,18,19,20",
            "speed": "100000",
            "index": "25",
            "admin_status": "up",
            "mtu": "9100"
        },
        "Ethernet100": {
            "alias": "Eth26",
            "lanes": "21,22,23,24",
            "speed": "100000",
            "index": "26",
            "admin_status": "up",
            "mtu": "9100"
        },
        "Ethernet104": {
            "alias": "Eth27",
            "lanes": "25,26,27,28",
            "speed": "100000",
            "index": "27",
            "admin_status": "up",
            "mtu": "9100"
        },
        "Ethernet108": {
            "alias": "Eth28",
            "lanes": "29,30,31,32",
            "speed": "100000",
            "index": "28",
            "admin_status": "up",
            "mtu": "9100"
        },
        "Ethernet112": {
            "alias": "Eth29",
            "lanes": "113,114,115,116",
            "speed": "100000",
            "index": "29",
            "admin_status": "up",
            "mtu": "9100"
        },
        "Ethernet116": {
            "alias": "Eth30",
            "lanes": "117,118,119,120",
            "speed": "100000",
            "index": "30",
            "admin_status": "up",
            "mtu": "9100"
        },
        "Ethernet120": {
            "alias": "Eth31",
            "lanes": "121,122,123,124",
            "speed": "100000",
            "index": "31",
            "admin_status": "up",
            "mtu": "9100"
        },
        "Ethernet124": {
            "alias": "Eth32",
            "lanes": "125,126,127,128",
            "speed": "100000",
            "index": "32",
            "admin_status": "up",
            "mtu": "9100"
        }
    },
    "BREAKOUT_CFG": {
        "Ethernet0": {
            "brkout_mode": "4x25G[10G]"
        },
        "Ethernet4": {
            "brkout_mode": "1x100G[40G]"
        },
        "Ethernet8": {
            "brkout_mode": "1x100G[40G]"
        },
        "Ethernet12": {
            "brkout_mode": "1x100G[40G]"
        },
        "Ethernet16": {
            "brkout_mode": "1x100G[40G]"
        },
        "Ethernet20": {
            "brkout_mode": "1x100G[40G]"
        },
        "Ethernet24": {
            "brkout_mode": "1x100G[40G]"
        },
        "Ethernet28": {
            "brkout_mode": "1x100G[40G]"
        },
        "Ethernet32": {
            "brkout_mode": "1x100G[40G]"
        },
        "Ethernet36": {
            "brkout_mode": "1x100G[40G]"
        },
        "Ethernet40": {
            "brkout_mode": "1x100G[40G]"
        },
        "Ethernet44": {
            "brkout_mode": "1x100G[40G]"
        },
        "Ethernet48": {
            "brkout_mode": "1x100G[40G]"
        },
        "Ethernet52": {
            "brkout_mode": "1x100G[40G]"
        },
        "Ethernet56": {
            "brkout_mode": "1x100G[40G]"
        },
        "Ethernet60": {
            "brkout_mode": "1x100G[40G]"
        },
        "Ethernet64": {
            "brkout_mode": "1x100G[40G]"
        },
        "Ethernet68": {
            "brkout_mode": "1x100G[40G]"
        },
        "Ethernet72": {
            "brkout_mode": "1x100G[40G]"
        },
        "Ethernet76": {
            "brkout_mode": "1x100G[40G]"
        },
        "Ethernet80": {
            "brkout_mode": "4x25G[10G]"
        },
        "Ethernet84": {
            "brkout_mode": "1x100G[40G]"
        },
        "Ethernet88": {
            "brkout_mode": "1x100G[40G]"
        },
        "Ethernet92": {
            "brkout_mode": "1x100G[40G]"
        },
        "Ethernet96": {
            "brkout_mode": "1x100G[40G]"
        },
        "Ethernet100": {
            "brkout_mode": "1x100G[40G]"
        },
        "Ethernet104": {
            "brkout_mode": "1x100G[40G]"
        },
        "Ethernet108": {
            "brkout_mode": "1x100G[40G]"
        },
        "Ethernet112": {
            "brkout_mode": "1x100G[40G]"
        },
        "Ethernet116": {
            "brkout_mode": "1x100G[40G]"
        },
        "Ethernet120": {
            "brkout_mode": "1x100G[40G]"
        },
        "Ethernet124": {
            "brkout_mode": "1x100G[40G]"
        }
    },
    "LOOPBACK_INTERFACE": {
        "Loopback0|10.1.0.1/32": {}
    },
    "BGP_NEIGHBOR": {
        "10.0.0.1": {
            "rrclient": 0,
            "name": "ARISTA01T2",
            "local_addr": "10.0.0.0",
            "nhopself": 0,
            "holdtime": "180",
            "asn": "65200",
            "keepalive": "60"
        },
        "10.0.0.3": {
            "rrclient": 0,
            "name": "ARISTA02T2",
            "local_addr": "10.0.0.2",
            "nhopself": 0,
            "holdtime": "180",
            "asn": "65200",
            "keepalive": "60"
        },
        "10.0.0.5": {
            "rrclient": 0,
            "name": "ARISTA03T2",
            "local_addr": "10.0.0.4",
            "nhopself": 0,
            "holdtime": "180",
            "asn": "65200",
            "keepalive": "60"
        },
        "10.0.0.7": {
            "rrclient": 0,
            "name": "ARISTA04T2",
            "local_addr": "10.0.0.6",
            "nhopself": 0,
            "holdtime": "180",
            "asn": "65200",
            "keepalive": "60"
        },
        "10.0.0.9": {
            "rrclient": 0,
            "name": "ARISTA05T2",
            "local_addr": "10.0.0.8",
            "nhopself": 0,
            "holdtime": "180",
            "asn": "65200",
            "keepalive": "60"
        },
        "10.0.0.11": {
            "rrclient": 0,
            "name": "ARISTA06T2",
            "local_addr": "10.0.0.10",
            "nhopself": 0,
            "holdtime": "180",
            "asn": "65200",
            "keepalive": "60"
        },
        "10.0.0.13": {
            "rrclient": 0,
            "name": "ARISTA07T2",
            "local_addr": "10.0.0.12",
            "nhopself": 0,
            "holdtime": "180",
            "asn": "65200",
            "keepalive": "60"
        },
        "10.0.0.15": {
            "rrclient": 0,
            "name": "ARISTA08T2",
            "local_addr": "10.0.0.14",
            "nhopself": 0,
            "holdtime": "180",
            "asn": "65200",
            "keepalive": "60"
        },
        "10.0.0.17": {
            "rrclient": 0,
            "name": "ARISTA09T2",
            "local_addr": "10.0.0.16",
            "nhopself": 0,
            "holdtime": "180",
            "asn": "65200",
            "keepalive": "60"
        },
        "10.0.0.19": {
            "rrclient": 0,
            "name": "ARISTA10T2",
            "local_addr": "10.0.0.18",
            "nhopself": 0,
            "holdtime": "180",
            "asn": "65200",
            "keepalive": "60"
        },
        "10.0.0.21": {
            "rrclient": 0,
            "name": "ARISTA11T2",
            "local_addr": "10.0.0.20",
            "nhopself": 0,
            "holdtime": "180",
            "asn": "65200",
            "keepalive": "60"
        },
        "10.0.0.23": {
            "rrclient": 0,
            "name": "ARISTA12T2",
            "local_addr": "10.0.0.22",
            "nhopself": 0,
            "holdtime": "180",
            "asn": "65200",
            "keepalive": "60"
        },
        "10.0.0.25": {
            "rrclient": 0,
            "name": "ARISTA13T2",
            "local_addr": "10.0.0.24",
            "nhopself": 0,
            "holdtime": "180",
            "asn": "65200",
            "keepalive": "60"
        },
        "10.0.0.27": {
            "rrclient": 0,
            "name": "ARISTA14T2",
            "local_addr": "10.0.0.26",
            "nhopself": 0,
            "holdtime": "180",
            "asn": "65200",
            "keepalive": "60"
        },
        "10.0.0.29": {
            "rrclient": 0,
            "name": "ARISTA15T2",
            "local_addr": "10.0.0.28",
            "nhopself": 0,
            "holdtime": "180",
            "asn": "65200",
            "keepalive": "60"
        },
        "10.0.0.31": {
            "rrclient": 0,
            "name": "ARISTA16T2",
            "local_addr": "10.0.0.30",
            "nhopself": 0,
            "holdtime": "180",
            "asn": "65200",
            "keepalive": "60"
        },
        "10.0.0.33": {
            "rrclient": 0,
            "name": "ARISTA01T0",
            "local_addr": "10.0.0.32",
            "nhopself": 0,
            "holdtime": "180",
            "asn": "64001",
            "keepalive": "60"
        },
        "10.0.0.35": {
            "rrclient": 0,
            "name": "ARISTA02T0",
            "local_addr": "10.0.0.34",
            "nhopself": 0,
            "holdtime": "180",
            "asn": "64002",
            "keepalive": "60"
        },
        "10.0.0.37": {
            "rrclient": 0,
            "name": "ARISTA03T0",
            "local_addr": "10.0.0.36",
            "nhopself": 0,
            "holdtime": "180",
            "asn": "64003",
            "keepalive": "60"
        },
        "10.0.0.39": {
            "rrclient": 0,
            "name": "ARISTA04T0",
            "local_addr": "10.0.0.38",
            "nhopself": 0,
            "holdtime": "180",
            "asn": "64004",
            "keepalive": "60"
        },
        "10.0.0.41": {
            "rrclient": 0,
            "name": "ARISTA05T0",
            "local_addr": "10.0.0.40",
            "nhopself": 0,
            "holdtime": "180",
            "asn": "64005",
            "keepalive": "60"
        },
        "10.0.0.43": {
            "rrclient": 0,
            "name": "ARISTA06T0",
            "local_addr": "10.0.0.42",
            "nhopself": 0,
            "holdtime": "180",
            "asn": "64006",
            "keepalive": "60"
        },
        "10.0.0.45": {
            "rrclient": 0,
            "name": "ARISTA07T0",
            "local_addr": "10.0.0.44",
            "nhopself": 0,
            "holdtime": "180",
            "asn": "64007",
            "keepalive": "60"
        },
        "10.0.0.47": {
            "rrclient": 0,
            "name": "ARISTA08T0",
            "local_addr": "10.0.0.46",
            "nhopself": 0,
            "holdtime": "180",
            "asn": "64008",
            "keepalive": "60"
        },
        "10.0.0.49": {
            "rrclient": 0,
            "name": "ARISTA09T0",
            "local_addr": "10.0.0.48",
            "nhopself": 0,
            "holdtime": "180",
            "asn": "64009",
            "keepalive": "60"
        },
        "10.0.0.51": {
            "rrclient": 0,
            "name": "ARISTA10T0",
            "local_addr": "10.0.0.50",
            "nhopself": 0,
            "holdtime": "180",
            "asn": "64010",
            "keepalive": "60"
        },
        "10.0.0.53": {
            "rrclient": 0,
            "name": "ARISTA11T0",
            "local_addr": "10.0.0.52",
            "nhopself": 0,
            "holdtime": "180",
            "asn": "64011",
            "keepalive": "60"
        },
        "10.0.0.55": {
            "rrclient": 0,
            "name": "ARISTA12T0",
            "local_addr": "10.0.0.54",
            "nhopself": 0,
            "holdtime": "180",
            "asn": "64012",
            "keepalive": "60"
        },
        "10.0.0.57": {
            "rrclient": 0,
            "name": "ARISTA13T0",
            "local_addr": "10.0.0.56",
            "nhopself": 0,
            "holdtime": "180",
            "asn": "64013",
            "keepalive": "60"
        },
        "10.0.0.59": {
            "rrclient": 0,
            "name": "ARISTA14T0",
            "local_addr": "10.0.0.58",
            "nhopself": 0,
            "holdtime": "180",
            "asn": "64014",
            "keepalive": "60"
        },
        "10.0.0.61": {
            "rrclient": 0,
            "name": "ARISTA15T0",
            "local_addr": "10.0.0.60",
            "nhopself": 0,
            "holdtime": "180",
            "asn": "64015",
            "keepalive": "60"
        },
        "10.0.0.63": {
            "rrclient": 0,
            "name": "ARISTA16T0",
            "local_addr": "10.0.0.62",
            "nhopself": 0,
            "holdtime": "180",
            "asn": "64016",
            "keepalive": "60"
        }
    },
    "DEVICE_NEIGHBOR": {},
    "INTERFACE": {
        "Ethernet0|10.0.0.0/31": {},
        "Ethernet4|10.0.0.2/31": {},
        "Ethernet8|10.0.0.4/31": {},
        "Ethernet12|10.0.0.6/31": {},
        "Ethernet16|10.0.0.8/31": {},
        "Ethernet20|10.0.0.10/31": {},
        "Ethernet24|10.0.0.12/31": {},
        "Ethernet28|10.0.0.14/31": {},
        "Ethernet32|10.0.0.16/31": {},
        "Ethernet36|10.0.0.18/31": {},
        "Ethernet40|10.0.0.20/31": {},
        "Ethernet44|10.0.0.22/31": {},
        "Ethernet48|10.0.0.24/31": {},
        "Ethernet52|10.0.0.26/31": {},
        "Ethernet56|10.0.0.28/31": {},
        "Ethernet60|10.0.0.30/31": {},
        "Ethernet64|10.0.0.32/31": {},
        "Ethernet68|10.0.0.34/31": {},
        "Ethernet72|10.0.0.36/31": {},
        "Ethernet76|10.0.0.38/31": {},
        "Ethernet80|10.0.0.40/31": {},
        "Ethernet84|10.0.0.42/31": {},
        "Ethernet88|10.0.0.44/31": {},
        "Ethernet92|10.0.0.46/31": {},
        "Ethernet96|10.0.0.48/31": {},
        "Ethernet100|10.0.0.50/31": {},
        "Ethernet104|10.0.0.52/31": {},
        "Ethernet108|10.0.0.54/31": {},
        "Ethernet112|10.0.0.56/31": {},
        "Ethernet116|10.0.0.58/31": {},
        "Ethernet120|10.0.0.60/31": {},
        "Ethernet124|10.0.0.62/31": {}
    },
    "KDUMP": {
        "config": {
            "enabled": "false",
            "num_dumps": "3",
            "memory": "0M-2G:256M,2G-4G:320M,4G-8G:384M,8G-:448M"
        }
    }