**- Why I did it**
I was asked to change "Allow list" prefix-list generation rule.
Previously we generated the rules using following method:
```
For each {prefix}/{masklen} we would generate the prefix-rule
permit {prefix}/{masklen} ge {masklen}+1
Example:
Prefix 1.2.3.4/24 would have following prefix-list entry generated
permit 1.2.3.4/24 ge 23
```
But we discovered the old rule doesn't work for all cases we have.
So we introduced the new rule:
```
For ipv4 entry,
For mask < 32 , we will add ‘le 32’ to cover all prefix masks to be sent by T0
For mask =32 , we will not add any ‘le mask’
For ipv6 entry, we will add le 128 to cover all the prefix mask to be sent by T0
For mask < 128 , we will add ‘le 128’ to cover all prefix masks to be sent by T0
For mask = 128 , we will not add any ‘le mask’
```
**- How I did it**
I change prefix-list entry generation function. Also I introduced a test for the changed function.
**- How to verify it**
1. Build an image and put it on your dut.
2. Create a file test_schema.conf with the test configuration
```
{
"BGP_ALLOWED_PREFIXES": {
"DEPLOYMENT_ID|0|1010:1010": {
"prefixes_v4": [
"10.20.0.0/16",
"10.50.1.0/29"
],
"prefixes_v6": [
"fc01:10::/64",
"fc02:20::/64"
]
},
"DEPLOYMENT_ID|0": {
"prefixes_v4": [
"10.20.0.0/16",
"10.50.1.0/29"
],
"prefixes_v6": [
"fc01:10::/64",
"fc02:20::/64"
]
}
}
}
```
3. Apply the configuration by command
```
sonic-cfggen -j test_schema.conf --write-to-db
```
4. Check that your bgp configuration has following prefix-list entries:
```
admin@str-s6100-acs-1:~$ show runningconfiguration bgp | grep PL_ALLOW
ip prefix-list PL_ALLOW_LIST_DEPLOYMENT_ID_0_COMMUNITY_1010:1010_V4 seq 10 deny 0.0.0.0/0 le 17
ip prefix-list PL_ALLOW_LIST_DEPLOYMENT_ID_0_COMMUNITY_1010:1010_V4 seq 20 permit 127.0.0.1/32
ip prefix-list PL_ALLOW_LIST_DEPLOYMENT_ID_0_COMMUNITY_1010:1010_V4 seq 30 permit 10.20.0.0/16 le 32
ip prefix-list PL_ALLOW_LIST_DEPLOYMENT_ID_0_COMMUNITY_1010:1010_V4 seq 40 permit 10.50.1.0/29 le 32
ip prefix-list PL_ALLOW_LIST_DEPLOYMENT_ID_0_COMMUNITY_empty_V4 seq 10 deny 0.0.0.0/0 le 17
ip prefix-list PL_ALLOW_LIST_DEPLOYMENT_ID_0_COMMUNITY_empty_V4 seq 20 permit 127.0.0.1/32
ip prefix-list PL_ALLOW_LIST_DEPLOYMENT_ID_0_COMMUNITY_empty_V4 seq 30 permit 10.20.0.0/16 le 32
ip prefix-list PL_ALLOW_LIST_DEPLOYMENT_ID_0_COMMUNITY_empty_V4 seq 40 permit 10.50.1.0/29 le 32
ipv6 prefix-list PL_ALLOW_LIST_DEPLOYMENT_ID_0_COMMUNITY_1010:1010_V6 seq 10 deny ::/0 le 59
ipv6 prefix-list PL_ALLOW_LIST_DEPLOYMENT_ID_0_COMMUNITY_1010:1010_V6 seq 20 deny ::/0 ge 65
ipv6 prefix-list PL_ALLOW_LIST_DEPLOYMENT_ID_0_COMMUNITY_1010:1010_V6 seq 30 permit fc01:10::/64 le 128
ipv6 prefix-list PL_ALLOW_LIST_DEPLOYMENT_ID_0_COMMUNITY_1010:1010_V6 seq 40 permit fc02:20::/64 le 128
ipv6 prefix-list PL_ALLOW_LIST_DEPLOYMENT_ID_0_COMMUNITY_empty_V6 seq 10 deny ::/0 le 59
ipv6 prefix-list PL_ALLOW_LIST_DEPLOYMENT_ID_0_COMMUNITY_empty_V6 seq 20 deny ::/0 ge 65
ipv6 prefix-list PL_ALLOW_LIST_DEPLOYMENT_ID_0_COMMUNITY_empty_V6 seq 30 permit fc01:10::/64 le 128
ipv6 prefix-list PL_ALLOW_LIST_DEPLOYMENT_ID_0_COMMUNITY_empty_V6 seq 40 permit fc02:20::/64 le 128
```
Co-authored-by: Pavel Shirshov <pavel.contrib@gmail.com>
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