Interface And Hardware Component Configuration Guide For Cisco Ncs 5500 Series Routers, Ios Xr Release - Cisco NCS 5500 Series Configuration Manual

Configuring Ethernet OAM
This figure shows an example of CFM linktrace message flow between MEPs and MIPs.
Figure 6: Linktrace Message Flow
The linktrace mechanism is designed to provide useful information even after a network failure. This allows
it to be used to locate failures, for example after a loss of continuity is detected. To achieve this, each MP
maintains a CCM Learning Database. This maps the source MAC address for each received CCM to the
interface through which the CCM was received. It is similar to a typical bridge MAC learning database, except
that it is based only on CCMs and it times out much more slowly—on the order of days rather than minutes.
In IEEE 802.1ag, the CCM Learning Database is referred to as the MIP CCM Database. However, it
Note
applies to both MIPs and MEPs.
In IEEE 802.1ag, when an MP receives an LTM message, it determines whether to send a reply using the
following steps:
1 The target MAC address in the LTM is looked up in the bridge MAC learning table. If the MAC address
is known, and therefore the egress interface is known, then an LTR is sent.
2 If the MAC address is not found in the bridge MAC learning table, then it is looked up in the CCM learning
database. If it is found, then an LTR is sent.
3 If the MAC address is not found, then no LTR is sent (and the LTM is not forwarded).
If the target MAC has never been seen previously in the network, the linktrace operation will not produce any
results.
Interface and Hardware Component Configuration Guide for Cisco NCS 5500 Series Routers, IOS XR Release 6.1.x
Ethernet CFM
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