RDP node configuration. Possible values:
- unknown: the node configuration is unknown.
- is: Intermediate System. The node is expected to have both an East and
a West neighbor node in the Appian DCC ring.
- ese: End System East. The node is expected to only have a West neighbor
node in the Appian DCC ring.
- esw: End System West. The node is expected to only have an East neighbor
node in the Appian DCC ring.