3-3
As shown in
, an outward-facing MEP sends packets to its host port.
Figure 3-3
Inward-facing MEP
As shown in
, an inward-facing MEP does not send packets to its host port. Rather, it sends
packets to other ports on the device.
z
MIP
A MIP is internal to an MD. It cannot send CFD packets actively; however, it can handle and respond
to CFD packets. The MA and MD to which a MIP belongs define the VLAN attribute and level of the
packets received.
By cooperating with MEPs, a MIP can perform a function similar to ping and traceroute. Like a MEP, a
MIP forwards packets at a higher level without any processing and only processes packet of its level or
lower.
demonstrates a grading example of the CFD module. In the figure, there are six devices,
labeled A through F respectively. Suppose each device has two ports, and MEPs and MIPs are
configured on some of these ports. Four levels of MDs are designed in this example, the bigger the
number, the higher the level and the larger the area covered. In this example, Port 1 of device B is
configured with the following MPs: a level 5 MIP, a level 3 inward-facing MEP, a level 2 inward-facing
MEP, and a level 0 outward-facing MEP.
Figure 3-4
Levels of MPs
Device A
Device B
Device C
Device D
Device E
Device F
5
5
3
5
5
3
3
3
2
2
2
2
0
0
0
0
0
0
MD level 5
MD level 3
MD Level 2
MD Level 2
MD level 0
Port
5
Outward-facing MEP and MD level
5
MIP and MD level
Maintenance association
Logical path of CFD messages
Port 1
Port 2
MD level 0
MD level 0
3
Inward-facing MEP and MD level
2
2
2
2
