Cisco ASR 9000 Series Configuration Manuallines page 387

Implementing IEEE 802.1ah Provider Backbone Bridge
Multiple I-SID Registration Protocol Lite
network. A backbone edge bridge (BEB) signals to other potentially affected BEBs, the need to alter certain
learned associations between customer MAC addresses and backbone MAC addresses. In the absence of
MIRP, customer connections across a provider backbone network can take several minutes to restore
connectivity after a topology change in an access network.
In prior releases, PBB traffic was dropped for a MAC aging cycle when bridge forwarding topology changes
occurred (due to unavailable ports or spanning tree topology changes) in a PBB edge bridge domain. This
resulted in severe limitations for the use of PBB bridges.
Cisco ASR 9000 Series Aggregation Services Routers now support a simplified implementation of the MIRP
protocol known as the Multiple I-SID Registration Protocol Lite (MIRP-Lite). The MIRP-Lite feature enables
detection of a topology change at a site. A specially defined packet is flooded to all remote edge sites of the
PBB network when a site detects a topology change. At the sender site, I-SID of the I-component is placed
in the I-TAG of the frame header to specify the I-SID that needs a MAC flush. At the receiver site, each PBB
edge switch performs I-SID checking. If the I-SID matches one of the I-components, the MAC in the
I-component is flushed.
The use of MIRP in 802.1ah networks is illustrated in the following figure.
Figure 43: MIRP in 802.1ah Networks
Device DHD1 is dual-homed to two 802.1ah backbone edge bridges (BEB1 and BEB2). Assume that initially
the primary path is through BEB1. In this configuration BEB3 learns that the host behind DHD1 (with MAC
address CM1) is reachable via the destination B-MAC M1. If the link between DHD1 and BEB1 fails and
the host behind DHD1 remains inactive, the MAC cache tables on BEB3 still refer to the BEB1 MAC address
even though the new path is now via BEB2 with B-MAC address M2. Any bridged traffic destined from the
host behind DHD2 to the host behind DHD1 is wrongly encapsulated with B-MAC M1 and sent over the
MAC tunnel to BEB1, where the traffic drops.
L2VPN and Ethernet Services Configuration Guide for Cisco ASR 9000 Series Routers, IOS XR Release 6.3.x
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