EXFO FTB-8500 Series for FTB-500 - Manual (Page 237)

Stream Generation Tabs
Ethernet and Fibre Channel Application 223
IP/UDP/TCP
IP/UDP/TCP
Note: Only available when the network stream configuration is set to IPv4,
MPLS/IPv4, IPv6, or MPLS/IPv6.
Press TEST, Stream Gen, and IP/UDP/TCP.
Stream No.
For Frame Analyzer test, select the stream number from the list. Only
stream number 1 is available for RFC 2544 and BERT tests.
Source
For IPv4:

IP Address: Enter the IP address for the selected stream. The default
setting is 10.10.x.x, where x and y are respectively the two least
significant bytes of the port default MAC address.

Subnet Mask: Enter the Subnet Mask for the selected stream. The
default setting is 255.255.0.0.