# ndnping and ndnpingserver

## Introduction

**ndnping** and **ndnpingserver** are reachability testing tools for NDN. They can be used
to test the network reachability between two nodes. The client sends an Interest intended
for a node running **ndnpingserver**. The server then sends Data in response. The client
then calculates the roundtrip time for the Interest-Data exchange, or marks it as a timeout
if the Data packet is not received within the timeout period.

## Using the client

The client can be invoked by calling `ndnping` with a name to ping. For example, to ping
`/edu/arizona`, one would run:

    ndnping /edu/arizona

There are also a variety of options to control the behavior of the ping client. For example,
to send only four pings to `/edu/arizona`, displaying a timestamp with each received Data or
timeout, type:

    ndnping -c 4 -t /edu/arizona

A list of the available options can be found with `man ndnping`.

## Using the server

The server can be invoked by calling `ndnpingserver` with a name to listen for pings to. For
example, to listen for pings to `/edu/arizona`, one would run:

    ndnpingserver /edu/arizona

There are also a variety of options to control the behavior of the ping server. For example,
to satisfy only 4 ping requests before exiting, run the following:

    ndnpingserver -p 4 /edu/arizona

A list of the available options can be found with `man ndnpingserver`.

## NDN ping protocol

This section briefly describes ndnping's protocol, in order to allow alternate implementations
to be compatible with this implementation.

The current protocol version is **ndnping protocol version 1**.
This version number will be incremented whenever there is an incompatible change.

### Probe Interests

The client expresses probe Interests that are intended to be forwarded to the server
without being aggregated.
The Interests MUST have one of the following name structures:

    ndn:/<prefix>/ping/<seq>
    ndn:/<prefix>/ping/<client-identifier>/<seq>

where:

* `<prefix>` is the server prefix that contains zero or more NameComponents.
* `<seq>` is one NameComponent whose value is an unsigned 64-bit integer, represented as
  a decimal number in ASCII encoding.
* `<client-identifier>` is one NameComponent with arbitrary value.

If a client expresses multiple probe Interests, it is RECOMMENDED for those Interests to
have consecutive increasing integers in `<seq>` field.

If a client uses the name structure with `<client-identifier>` field, it is RECOMMENDED to use
one or more printable characters only, to make it easier for a human operator to read the logs.
A client implementation MAY restrict this field to be non-empty and have printable characters only.

The probe Interest SHOULD NOT carry CanBePrefix element.

The probe Interest SHOULD carry MustBeFresh element.
A client implementation MAY allow the operator to remove MustBeFresh element.

### Reply Data

The server SHOULD register the prefix `ndn:/<prefix>/ping`, and MUST reply to probe Interests
under this prefix with Data.
The Data MUST have the same name as the probe Interest.

The Data MUST have BLOB as its ContentType.
The Data MAY have arbitrary payload in its Content field.
A server implementation MAY allow the operator to configure the length and contents of the payload.

The Data SHOULD have a valid signature.
The server SHOULD use DigestSha256 signature by default.
A server implementation MAY allow the operator to configure a different signature algorithm.
The client SHOULD NOT verify the signature by default.
A client implementation MAY allow the operator to enable signature verification.