IBM 9077 User Manual

IBM 9077 SP Switch Router: Get Connected to the SP Switch

This Chapter describes the GRF bridging implementation and provides 
configuration information.

The GRF implements IEEE 802.1d transparent bridging on GRF Ethernet and 
FDDI interfaces, and on ATM OC-3c interfaces using RFC-1483 
encapsulated bridging over PVCs.

Transparent bridging provides a mechanism for interconnecting stations 
attached to physically separate Local Area Networks (LANs) as if they are 
attached to a single LAN. This interconnection happens at the 802 MAC layer 
and is transparent to protocols operating above this boundary in the Logical 
Link Control (LLC) or Network layers. Participating stations are unable to 
identify that peers are on anything other than the directly attached physical 
media.

The GRF implementation consists of the transparent bridging function 
described in 802.1d, and does not include any capability for Source Route or 
Source Route Transparent (SRT) bridge operation.

Summary of bridging features:

  • Bridging on FDDI, Ethernet, and ATM OC-3c per the 802.1d standard

  • Participation in 802.1d spanning tree protocol

  • Layer-2 transparent bridging of MAC frames through the GRF from one 

interface to another

  • Conversion of frames between Ethernet and FDDI formats as necessary

  • Fragmentation of IPv4 frames if necessary

  • Simultaneous bridging and routing over the same interface (a GRF 

interface participating in a bridge group can still route normally)

  • Routing IP to or from a bridge group from any GRF media

  • RFC-1483 encapsulated bridging over ATM OC-3c PVCs with either 

VC-based multiplexing or LLC encapsulation

  • Up to 16 bridge groups per GRF

  • Up to 32 GRF interfaces per bridge group