NETCONF messages sent by OpenDaylight cannot be parsed by Cisco routers

Cisco routers expect that NETCONF messages are prefixed by the XML declaration:

<?xml version="1.0" encoding="UTF-8"?>

Else, they close the NETCONF/SSH connection and log an error such as:

NETCONF-ERROR: parse error before hello seen

NETCONF messages sent by the OpenDaylight controller (eg the <hello> message) are not prefixed with that XML declaration. Consequently, Cisco routers reject them and close the NETCONF/SSH connection.

This has been observed with the follwoing Cisco equipments and IOS versions:

• CSR1000V (virtual routeur) with IOS 15.4(1)S
• ASR1001-X with IOS 15.4(2)S0a
• ISR2900 with IOS 15.1(4)M1

A test program that can be used to reproduce the problem with a Cisco router can be found in the related bug report: https://bugs.opendaylight.org/show_bug.cgi?id=2877.

Whether the NETCONF RFC mandates the presence of the XML declaration is unclear to me. So I don't know if this is a bug in OpenDaylight or a bug in Cisco routers.

I will propose a patch to fix/workaround the problem in OpenDaylight.