User`s guide

Introduction

1-15

multicast packets.

If source routing is desired, and either Ethernet or FDDI is to be

used as a backbone between Token Rings, then the Ethernet or

FDDI port should be conﬁgured for SRT bridging. (SRT over

Ethernet is not a standard, but is available for use between

multiple ATX chassis in backbone applications. In this case, the

“Ethernet” may actually be a microwave or satellite link with an

Ethernet-like interface.)

A common mixture of bridging modes may occur when Ethernet

segments and Token Ring segments do not exchange data but

share an FDDI backbone. In this case, the Ethernets may be

conﬁgured for transparent bridging, the Token Rings for source

routing, and the FDDI backbone for SRT. (Don't infer from this

example that SRT is the sum of transparent and source routing

bridging; it is a distinct third method).

The bridging method is dependent on the conﬁguration of the

bridge entry and exit ports, and the value of the Routing Indicator

(RII) bit in the received frame. The following chart summarizes the

interaction between the bridging method.

a. source address is not learned

Exit Port Conﬁguration

Entry

Port

Conﬁg.

RII

SRT

(Source

Routing

Transparent)

(Source

Routing)

TST

(Transparent

Spanning

Tree)

SRT 0 spanning tree block spanning tree

1 source route source route spanning tree

SR 0 block block block

1 source route block block

TST 0 spanning tree block spanning tree

1 spanning tree

block spanning tree