Brocade Multi-Service IronWare Administration Guide (Supporting R05.6.00) - Manual (Page 166)

148 Multi-Service IronWare Administration Guide
53-1003028-02
Mechanisms of Ethernet IEEE 802.1ag OAM
6
As a result, MEPs also receive CCMs periodically from other MEPs. If a MEP on local Bridge stops
receiving the periodic CCMs from peer MEP on a remote Bridge, it can assume that either the
remote Bridge has failed or failure in the continuity of the path has occurred. The Bridge can
subsequently notify the network management application about the failure and initiate the fault
verification and fault isolation steps either automatically or through operator command.
A CCM requires only N transmissions within its member group, where N is the number of members
within the member group. In other words, if a Virtual Bridge LAN Service has N members, only N
CCMs need to be transmitted periodically – one from each.
Continuity Check (CC) messages are periodic hello messages multicast by a MEP within the
maintenance domain, at the rate of X; X can be 3.3 milliseconds (ms), 10ms, or 100ms, 1 second,
1 minute, or 10 minutes. All Maintenance association Intermediate Points (MIPs) and MEPs in that
domain will receive it but will not respond to it. The receiving MEPs will build a MEP database that
has entities of the format. MEPs receiving this CC message will catalog it and know that the various
maintenance associations (MAs) are functional, including all intermediate MIPs.
NOTE
The Brocade NetIron CES does not support sub-second values.
CCMs are not directed towards any specific; rather they are multicast across the entire point-to-
point or multipoint service on a regular basis. Accordingly, one or more service flows, including the
determination of MAC address reachability across a multipoint network, are monitored for
connectivity status with IEEE 802.1ag.
Fault verification (Loopback messages)
A unicast Loopback Message is used for fault verification. To verify the connectivity between MEP
and its peer MEP or a MIP, the Loopback Message is initiated by a MEP with a destination MAC
address set to the MAC address of either a Maintenance association Intermediate Point (MIP) or
the peer MEP. The receiving MIP or MEP responds to the Loopback Message with a Loopback
Reply.
A Loopback message helps a MEP identify the precise fault location along a given MA. A Loopback
message is issued by a MEP to a given MIP along an MA. The appropriate MIP in front of the fault
will respond with a Loopback reply. The MIP behind the fault will not respond. For Loopback to
work, the MEP must know the MAC address of the MIP to ping.
Fault isolation (Linktrace messages)
Linktrace mechanism is used to isolate faults at Ethernet MAC layer. Linktrace can be used to
isolate a fault associated with a given Virtual Bridge LAN Service. It should be noted that fault
isolation in a connectionless (multi-point) environment is more challenging than a connection
oriented (point-to-point) environment. In case of Ethernet, fault isolation can be even more
challenging since a MAC address can age out when a fault isolates the MAC address. Consequently
a network-isolating fault results in erasure of information needed for locating the fault.
A Linktrace Message uses a set of reserved multicast MAC address. The Linktrace Message gets
initiated by a MEP and traverses hop-by-hop and each Maintenance Point (a MEP or MIP) along the
path intercepts this Linktrace Message and forwards it onto the next hop after processing it until it
reaches the destination MEP. The processing includes looking at the destination MAC address
contained in the Linktrace Message.