xref: /openbmc/docs/designs/multihost-ipmi-design.md (revision 0344dc18)

# Multi-host IPMI design

Author:
  Velumani T(velu),  [velumanit@hcl](mailto:velumanit@hcl.com)
  Kumar T(kumar_t), [thangavel.k@hcl.com](mailto:thangavel.k@hcl.com)

Primary assignee:

Other contributors:

Created:
 June 26, 2020

## Problem Description
The current version of OpenBMC does not support multi-host implementation in
IPMI commands handling. We have a multi-host system and proposing the design
to support multi-host.

As detailed below the hosts are connected in the IPMB interface, all host
related communication is based on IPMB. The OpenBMC uses ipmbbridged to manage
IPMB buses and the IPMB messages are routed to ipmid.

Issue 1: ipmbridged does not send the channel number (ie HostId)
Issue 2: ipmid does not have the information on which IPMB channel the request
has come from. The ipmid handlers should have the host details to fetch the
host specific responses.

## Background and References
IPMI and IPMB System architecture:
```
 +------------------------------------+
 |               BMC                  |
 | +-----------+       +------------+ |      +--------+
 | |           |       |            | | IPMB1|        |
 | |           |       |            |-|------| Host-1 |
 | |           |       |            | |      |        |
 | |           |       |            | |      +--------+
 | |           |       |            | |
 | |           |       |            | |
 | |           | D-Bus |            | |      +--------+
 | | ipmid     |-------| ipmbbridged| | IPMB2|        |
 | |           |       |            |-|------| Host-2 |
 | |           |       |            | |      |        |
 | |           |       |            | |      +--------+
 | |           |       |            | |
 | |           |       |            | |
 | |           |       |            | |      +--------+
 | |           |       |            | | IPMBn|        |
 | |           |       |            |-|------| Host-N |
 | |           |       |            | |      |        |
 | +-----------+       +------------+ |      +--------+
 +------------------------------------+
```
Hosts are connected with IPMB interface, the hosts can be 1 to N. The IPMB
request coming from the hosts are routed to ipmid by the ipmbbridged.
The IPMB requests are routed from ipmid or any service by D-Bus interface and
The outgoing IPMB requests are routed by ipmbbridged to IPMB interface.

## Requirements

The current version of OpenBMC does not support multi-host implementation in
IPMI commands handling. We have a multi-host system and proposing the design
to support multi-host.

## Proposed Design

To address issue1 and issue2, we propose the following design changes in
ipmbbridged and ipmid.
To address out-of-band IPMI command from the network,the proposal is captured
in section "Changes in netipmid".

Issue1: Changes in ipmbbridged:
-
ipmbbridged to send the channel details from where the request is received.

**Change: Sending Host detail as additional parameter**

While routing the IPMB requests coming from the host channel, We will be
adding new entry in the json config file for the host ID '"devIndex": 0'
ipmbbridged will send '"devIndex": 0' as optional parameter(options) in D-Bus
interface to ipmid.This can be used to get the information on which IPMB bus
the message comes from.

The json file looks like below. Each devIndex can have one "me" and "ipmb"
channel.To ensure existing platforms does not get affected, if the "devIndex"
key is not present in the file ipmbbridged uses default "devIndex" as 0.

{ "type": "me",
"slave-path": "/dev/ipmb-1",
"bmc-addr": 32,
"remote-addr": 64,
"devIndex": 0
},
{ "type": "ipmb",
"slave-path": "/dev/ipmb-2",
"bmc-addr": 32,
"remote-addr": 64,
"devIndex": 0
},
{ "type": "me",
"slave-path": "/dev/ipmb-3",
"bmc-addr": 32,
"remote-addr": 64,
"devIndex": 1
},
{ "type": "ipmb",
"slave-path": "/dev/ipmb-4",
"bmc-addr": 32,
"remote-addr": 64,
"devIndex": 1
},

Issue2: Changes in ipmid:
-
Receive the optional parameter sent by the ipmbbridged as host details, while
receiving the parameter in the executionEntry method call the same will be
passed to the command handlers in both common and oem handlers.The command
handlers can make use of the host information to fetch host specific data.

For example, host1 send a request to get boot order from BMC, BMC maintains
data separately for each host. When this command comes to ipmid the commands
handler gets the host in which the command received. The handler will fetch
host1 boot order details and respond from the command handler. This is
applicable for both common and oem handlers.

Changes in netipmid:
-
The "options" parameter can be used for sending the host information from
netipmid. The changes proposed for ipmbbridged can be used in netipmid as well.
The netipmid sends the "devIndex" on which channel the request comes from.
There will not be any further changes required in ipmid.
The netipmid can have multiple approaches to handle multi-host.Some of the
approaches are listed down and but not limited to this list.
1. Virtual Ethernet interfaces - One virtual interface per host.
2. Different port numbers - Can have different port numbers for each host.
3. VLAN Ids- VLAN IDs can be used to support multi host.
The netipmid shall have a config file where in the interfaces can be configured
for each host. Also one or more interfaces can be configured to each of the
host. The interfaces can be virtual or physical.
Below is the sample configuration file

{"Host":1,
"Interface-1":"eth0",
"Interface-2":"eth1",
"Interface-3":"veth4",
"Interface-4":"veth5"
},
{"Host":2,
"Interface-1":"eth2",
"Interface-2":"eth3",
"Interface-3":"veth1",
"Interface-4":"veth2"
},

Example implementation of approach1:Virtual ethernet interface.

```
+--------------------------------------------+
|           BMC                              |
| +--------+       +-----------+   +------+  |      +--------+
| |        | D-Bus |           |   |      |  |      |        |
| |        |-------| netipmid1 |---|veth1 |---------| Host-1 |
| |        |       |           |   |      |  |      |        |
| |        |       +-----------+   +------+  |      +--------+
| |        |                                 |
| |        |       +-----------+   +------+  |      +--------+
| | ipmid  | D-Bus |           |   |      |  |      |        |
| |        |-------| netipmid2 |---|veth2 |---------| Host-2 |
| |        |       |           |   |      |  |      |        |
| |        |       +-----------+   +------+  |      +--------+
| |        |                                 |
| |        |       +-----------+   +------+  |      +--------+
| |        | D-Bus |           |   |      |  |      |        |
| |        |-------| netipmidN |---|vethN |---------| Host-N |
| |        |       |           |   |      |  |      |        |
| +--------+       +-----------+   +------+  |      +--------+
+--------------------------------------------+
```
In the above diagram one instance of netipmid runs per host. Each instance
is tied to one virtual ethernet interface, The virutal interface ID can be
used to make a devIndex. This represents the HostId.

## Alternatives Considered

Approach1:ipmbbridged to send host-id in the payload
-
The ipmbbridged shall be modified to send the host id in data payload. This
looks to be a simple change but impacts the existing platforms which are already
using it.This may not be a right approach.

Approach2:Create multiple ipmid to handle multihost.One ipmid process per host.
-
This is a multi service appoach,one instance of ipmid service shall be
spawned to respond each host.The changes looks simple and no major design
change from the existing design. But many common handlers will be running as
duplicate in multiple instances.

Approach3:Using a different IPMI channel for handling multiple host.
-
Using a different IPMI channel for handling multiple hosts, in the ipmbbridged
the channel id can be used to identify host. In this approach we will be having
multiple instances of ipmbbridged and each instance will be registered with the
a channel number.Maximum channel numbers are limited to 8 as per the
specification.This limits the maximum hosts to be supported.

## Impacts

There may not be an impact in ipmid command handler functions.This design will
not affect the current functionality.

## Testing

The proposed design can be tested in a platform in which the multiple hosts
are connected.The commands requests are received from all the hosts and
responses are host specific data.When the request coming from the host as IPMB
command, ipmbbridged appends devIndex and ipmid receives the respective
devIndex.ipmid responds based on the received devIndex(Host Id) and
response reaches all the way to host.The data can be validated in host.