Routing Bridges (RBridges): Appointed Forwarders

Abstract

The IETF TRILL (TRansparent Interconnection of Lots of Links) protocol provides least cost pair-wise data forwarding without configuration in multi-hop networks with arbitrary topology, safe forwarding even during periods of temporary loops, and support for multipathing of both unicast and multicast traffic. TRILL accomplishes this by using IS-IS (Intermediate System to Intermediate System) link state routing and by encapsulating traffic using a header that includes a hop count. Devices that implement TRILL are called "RBridges" (Routing Bridges).

Transparent Interconnection of Lots of Links (TRILL): Appointed Forwarders

“…This document replaces and obsoletes [RFC6439], incorporating the former material in [RFC6439] with these additions. The various optimizations are orthogonal and optional.…”

Transparent Interconnection of Lots of Links (TRILL) Use of IS-IS

“…The Designated RBridge (DRB) on a link uses the Appointed Forwarders sub-TLV to inform other ISs on the link that they are the designated VLAN-x forwarder for one or more ranges of VLAN IDs as specified in [RFC6439]. It has the following format: o Length: 6*n bytes, where there are n appointments.…”

Directory Assistance Problem and High-Level Design Proposal

“…Assume S is an end station attached to RB1 trying to spoof a target end station T and that T is attached to RB2. Perhaps S wants to steal traffic intended for T or forge traffic as if it was from T. With that default TRILL data-plane learning as described in [RFC6325], S can impersonate T or any other end station in the same Data Label (VLAN or FGL [FGL]) as S and possibly other Data Labels, depending on how tightly VLAN admission and Appointed Forwarders [RFC6439] are configured at the port by which S is connected to RB1. S can just send native frames with the forged source MAC addresses of T, perhaps broadcast frames for maximum effectiveness.…”