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ipam.md

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IP address management (IPAM)

Overview

Sabakan assigns IP addresses to nodes for two purposes. One is for DHCP, and another is for static assignment. DHCP is used for the initial network boot.

Each machine may have one or more IP addresses for OS, and one for its [baseboard management controller][BMC].

IPAMConfig

IPAMConfig is a set of configurations to assign IP addresses automatically. It is given as JSON object with the following fields:

Field Type Description
max-nodes-in-rack int The maximum number of nodes in a rack, excluding "boot" node.
node-ipv4-pool string CIDR IPv4 network for node IP pool.
node-ipv4-offset string Node IPs will be started by adding this to node-ipv4-pool. Default is "", equivalent to 0.0.0.0.
node-ipv4-range-size int Size of the address range to divide the pool (bit counts).
node-ipv4-range-mask int The subnet mask for a divided range.
node-ip-per-node int The number of IP addresses for each node.
node-index-offset int Offset for assigning IP address to a node in a divided range.
node-gateway-offset int The default gateway address offset.
bmc-ipv4-pool string CIDR IPv4 network for BMC IP pool.
bmc-ipv4-offset string BMC IPs will be started by adding this to bmc-ipv4-pool. Default is "", equivalent to 0.0.0.0.
bmc-ipv4-range-size int Size of the address range to divide the pool (bit counts).
bmc-ipv4-range-mask int The subnet mask for a divided range.
bmc-ipv4-gateway-offset int The default gateway address offset.

Setting the index of a node

Upon node registration, sabakan sets the index in rack of the node.

Nodes whose role is "boot" will have node-index-offset as its index in rack. Other nodes will have an index ranging from node-index-offset + 1 to node-index-offset + max-nodes-in-rack.

Assigning static IPv4 addresses to Node OS

Sabakan computes static IPv4 addresses for a node OS as follows (pseudo code):

rack := node.RackNumber
idx  := node.IndexInRack

range_size := 1 << node-ipv4-range-size
base := INET_ATON(node-ipv4-pool) + INET_ATON(node-ipv4-offset)
addr0 := base + range_size * node-ip-per-node * rack + idx

addresses := []net.IP
for i := 0; i < node-ip-per-node; i++ {
    addresses = append(addresses, INET_NTOA(addr0 + i*range_size))
}

Assigning static IPv4 address to BMC

Sabakan computes static IPv4 addresses for BMC as follows (pseudo code):

rack := node.RackNumber
idx  := node.IndexInRack

range_size := 1 << bmc-ipv4-range-size
base := INET_ATON(bmc-ipv4-pool) + INET_ATON(bmc-ipv4-offset)

bmc_addr := INET_NTOA(base + range_size * rack + idx)

DHCP lease range

In short, sabakan leases IP addresses for DHCP that are never assigned statically to nodes.

Specifically, the range of IP addresses for lease begins from the next address of the node whose index in rack is node-index-offset + max-nodes-in-rack, and ends at the second last address of the divided range of the IP address pool.

Note that the divided range to be used can be determined by the interface address that accepts the DHCP request because the interface address must belong to the range. If the request was relayed by another DHCP server, the interface address of the relaying server should be used instead.

Examples

Suppose that IPAM configurations are as follows:

Field Value
max-nodes-in-rack 28
node-ipv4-pool 10.69.0.0/16
node-ipv4-offset 0.0.0.0
node-ipv4-range-size 6
node-ipv4-range-mask 26
node-ip-per-node 3
node-index-offset 3
node-gateway-offset 1
bmc-ipv4-pool 10.72.16.0/20
bmc-ipv4-offset 0.0.1.0
bmc-ipv4-range-size 5
bmc-ipv4-range-mask 20
bmc-ipv4-gateway-offset 1

For a node whose rack number is 0 and index in rack is 4, its static addresses for node OS are:

  • 10.69.0.4
  • 10.69.0.68
  • 10.69.0.132

and its BMC address is:

  • 10.72.17.4

For another node whose rack number is 1 and index in rack is 5, its static addresses for node OS are:

  • 10.69.0.197
  • 10.69.1.5
  • 10.69.1.69

and its BMC address is:

  • 10.72.17.37

Gateway address

A default gateway need to be given to clients to communicate with servers outside of the L2 network. The default gateway address is henceforth an address in the L2 network.

To calculate it automatically, sabakan uses node-gateway-offset as follows. Suppose the client has an IPv4 address "10.72.18.3",

  1. Mask the address with node-ipv4-range-mask bit mask.
  2. Add node-gateway-offset value.

With the given IPAM configurations, the gateway address is computed as "10.72.16.1".

The default gateway address for BMC is computed just like this but using bmc-ipv4-gateway-offset.