[Kea-users] Moving to implementing shared-networks

[Tim Požár]

I am working with a small ISP that got a /22 of v4 space and is using 
kea 1.6.2 in HA mode on two VMs.  From the /22 they use a /23 for DHCP 
customers.  The rest is for statics, loopbacks, etc.

The servers are sitting behind a Juniper MX104 using subscriber services 
so the stanard, get a dhcp packet with a particular DHCP Agent info of 
double tag, start to build the demux interface, look the customer up in 
Radius and assign them an IP address via DHCP and finish the demux 
interface on the last DHCP ACK.

They have nearly exhausted the /23 so they would like to add another 
small prefix (/26) to get them another 60 addresses or so to tied them 
over until the can pick up another /22 or so to move their dhcp 
customers too.

Working REDACTED config...
---
{
     "Dhcp4": {
         "interfaces-config": {
             "interfaces": [ "eth0", "eth1", "eth2" ]
         },
[...]
         "valid-lifetime": 4000,
         "renew-timer": 1000,
         "rebind-timer": 2000,
         "reservation-mode": "disabled",
         "control-socket": {
             "socket-type": "unix",
             "socket-name": "/tmp/kea-dhcp4-ctrl.sock"
         },
         "lease-database": {
             "type": "memfile",
             "persist": true,
             "name": "/var/lib/kea/kea-leases4.csv",
             "lfc-interval": 3600
         },
[...]
         "option-data": [
             {
                 "name": "domain-name-servers",
                 "data": "9.9.9.9, 8.8.8.8"
             }
         ],
[...]
         // For a list of available hook libraries, see 
https://gitlab.isc.org/isc-projects/kea/wikis/Hooks-available
         "hooks-libraries": [
             {
                 "library": "/usr/lib64/kea/hooks/libdhcp_ha.so",
                 "parameters": {
                     "high-availability": [
                         {
                             "this-server-name": "dhcp01",
                             "mode": "load-balancing",
                             "peers": [
                                 {
                                     "name": "dhcp01",
                                     "url": "http://10.1.9.2:8080/",
                                     "role": "primary"
                                 },
                                 {
                                     "name": "dhcp02",
                                     "url": "http://10.1.9.3:8080/",
                                     "role": "secondary"
                                 }
                             ]
                         }
                     ]
                 }
             }
         ],
         "subnet4": [
             {
                 // "name": "Networks",
                 "option-data": [
                     {
                         "data": "1.2.3.1",
                         "name": "routers"
                     }
                 ],
                 "pools": [{"pool": "1.2.3.2 - 1.2.4.254"}],
                 "reservations": [],
                 "subnet": "1.2.3.0/23",
                 "relay": {
                     "ip-addresses": [ "1.2.3.1","1.2.5.1" ]
                 }
             },
[...]

I moved the subnet4 stanza for the 1.2.3.1/23 pool to a shared-network 
stanza and added a new /26 that looks like:
[...]
         "shared-networks": [
             {
                 "name": "BNG-Users1",
                 "relay": {
                     "ip-addresses": [ "1.2.3.1","1.2.5.1" ]
                  },
                 "subnet4": [
                     {
                         // "name": "Customer Network Prefix #2",
                         "option-data": [
                             {
                                 "data": "1.2.5.1",
                                 "name": "routers"
                             }
                         ],
                         "pools": [{"pool": "1.2.5.2 - 1.2.5.62"}],
                         "reservations": [],
                         "subnet": "1.2.5.0/26",
                         "id": 5
                     },
                     {
                         // "name": "Customer Network Prefix #1",
                         "option-data": [
                             {
                                 "data": "1.2.3.1",
                                 "name": "routers"
                             }
                         ],
                         "pools": [{"pool": "1.2.3.2 - 1.2.4.254"}],
                         "reservations": [],
                         "subnet": "1.2.3.0/23",
                         "id": 110
                     }
                 ]
             }
         ],
[...]

In starting this up, it hands out the /26 pool and then doesn't assign 
much (6 to 12) from the old /23 pool.  Reversing the prefixes will mean 
it will only assign perhaps a dozen leases and then stops.

Running TCPDUMP on the Kea VMs I see a bunch of broken DHCP handshakes 
where I see:

DHCP Discover
DHCP Offer

and not the full handshake of:
DHCP Discover
DHCP Offer
DHCP Request
DHCP ACK

Or I will see a number of Discover/Offer exchanges and after some time a 
Discover/Offer/Request/ACK.

If I look at the API with something like:

curl -X POST -H "Content-Type: application/json" -d '{ "command": 
"stat-lease4-get","service": [ "dhcp4" ]}' http://127.0.0.1:8080/ | 
python3 -m json.tool
[
     {
         "arguments": {
             "result-set": {
                 "columns": [
                     "subnet-id",
                     "total-addreses",
                     "assigned-addreses",
                     "declined-addreses"
                 ],
                 "rows": [
                     [
                         1,
                         509,
                         499,
                         0
                     ],
                     [
                         2,
                         967,
                         0,
                         0
                     ],
                     [
                         3,
                         1013,
                         219,
                         0
                     ],
                     [
                         4,
                         1013,
                         0,
                         0
                     ]
                 ],
                 "timestamp": "2020-11-13 06:08:34.067055"
             }
         },
         "result": 0,
         "text": "stat-lease4-get[all subnets]: 4 rows found"
     }
]

This is an example of a working dhcp server.  If I try the 
shared-networks, the pools always show 0 assigned-addresses.

Is shared-networks pretty stable on 1.6.2?  Any suggestion on why only a 
small percent or none of these handshakes work?  Any suggestion on 
debugging this further?  I did create some rather large kea logs with 
logging set to DEBUG and debug set to 99 if that can be of help.

Tim Pozar