## Creating VPP Startup Configuration
This document describes how to create the VPP startup configuration
file located at `/etc/vpp/contiv-vswitch.conf`.

### Hardware Interface Configuration
#### Single-NIC Configuration
You need to configure hardware interfaces for use by VPP. First, find out the PCI address of the host's network interface. On 
Debian-based distributions, you can use `lshw`:

```
sudo lshw -class network -businfo
Bus info          Device      Class          Description
========================================================
pci@0000:03:00.0  ens160      network        VMXNET3 Ethernet Controller
```

In our case, it would be the `ens3` interface with the PCI address
`0000:00:03.0`

Now, add or modify the VPP startup config file (`/etc/vpp/contiv-vswitch.conf`)
to contain the proper PCI address:
```
unix {
    nodaemon
    cli-listen /run/vpp/cli.sock
    cli-no-pager
    coredump-size unlimited
    full-coredump
    poll-sleep-usec 100
}
nat {
    endpoint-dependent
}
dpdk {
    dev 0000:00:03.0
}
api-trace {
   on
   nitems 500
}
```
#### Multi-NIC Configuration
Similar to the single-NIC configuration, use command *lshw* to find the PCI
addresses of all the NICs in the system, for example:

```
$ sudo lshw -class network -businfo
Bus info          Device      Class      Description
====================================================
pci@0000:00:03.0  ens3        network    Virtio network device
pci@0000:00:04.0  ens4        network    Virtio network device
```

In the example above, `ens3` would be the primary interface and `ens4` would
be the interface that would be used by VPP. The PCI address of the `ens4`
interface would be `0000:00:04.0`.

Make sure the selected interface is *shut down*, otherwise VPP
will not grab it:
```
sudo ip link set ens4 down
```

Now, add or modify the VPP startup config file in `/etc/vpp/contiv-vswitch.conf`
to contain the proper PCI address:
```
unix {
    nodaemon
    cli-listen /run/vpp/cli.sock
    cli-no-pager
    coredump-size unlimited
    full-coredump
    poll-sleep-usec 100
}
nat {
    endpoint-dependent
}
dpdk {
    dev 0000:00:04.0
}
api-trace {
   on
   nitems 500
}
```
If assigning multiple NICs to VPP you will need to include each NIC's PCI address
in the dpdk stanza in `/etc/vpp/contiv-vswitch.conf`.

##### Assigning all NICs to VPP
On a multi-NIC node, it is also possible to assign all NICs from the kernel for
use by VPP. First, you need to install the STN daemon, as described [here][1],
since you will want the NICs to revert to the kernel if VPP crashes.

You also need to configure the NICs in the VPP startup config file
in `/etc/vpp/contiv-vswitch.conf`. For example, to use both the primary and
secondary NIC, in a two-NIC node, your VPP startup config file would look
something like this:

```
unix {
    nodaemon
    cli-listen /run/vpp/cli.sock
    cli-no-pager
    coredump-size unlimited
    full-coredump
    poll-sleep-usec 100
}
nat {
    endpoint-dependent
}
dpdk {
    dev 0000:00:03.0
    dev 0000:00:04.0
}
api-trace {
   on
   nitems 500
}
```

#### Installing `lshw` on CentOS/RedHat/Fedora
Note: On CentOS/RedHat/Fedora distributions, `lshw` may not be available
by default, install it by
```
sudo yum -y install lshw
```

### Power-saving Mode
In regular operation, VPP takes 100% of one CPU core at all times (poll loop).
If high performance and low latency is not required you can "slow-down"
the poll-loop and drastically reduce CPU utilization by adding the following 
stanza to the `unix` section of the VPP startup config file:
```
unix {
    ...
    poll-sleep-usec 100
    ...
}
```
The power-saving mode is especially useful in VM-based development environments 
running on laptops or less powerful servers. 

### VPP API Trace
To troubleshoot VPP configuration issues in production environments, it is 
strongly recommended to configure VPP API trace. This is done by adding the
following stanza to the VPP startup config file:
```
api-trace {
    on
    nitems 500
}
```
You can set the size of the trace buffer with the <nitems> attribute.