H3C S6850 Series, Configuration Manual

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packets and data packets through the intra-portal link (IPL) established between them. A DR
system has only one IPL.
DR member devices use a keepalive link to monitor each other's state. For more information about
the keepalive mechanism, see "
Keepalive and failover mechanism ."
DRCP
DRNI uses IEEE P802.1AX Distributed Relay Control Protocol (DRCP) for multichassis link
aggregation. DRCP runs on the IPL and uses distributed relay control protocol data units (DRCPDUs)
to advertise the DRNI configuration out of IPPs and DR interfaces.
DRCP operating mechanism
DRNI-enabled devices use DRCPDUs for the following purposes:
•
Exchange DRCPDUs through DR interfaces to determine whether they can form a DR system.
•
Exchange DRCPDUs through IPPs to negotiate the IPL state.
DRCP timeout timers
DRCP uses a timeout mechanism to specify the amount of time that an IPP or DR interface must wait
to receive DRCPDUs before it determines that the peer interface is down. This timeout mechanism
provides the following timer options:
•
Short DRCP timeout timer, which is fixed at 3 seconds. If this timer is used, the peer interface
sends one DRCPDU every second.
•
Long DRCP timeout timer, which is fixed at 90 seconds. If this timer is used, the peer interface
sends one DRCPDU every 30 seconds.
Short DRCP timeout timer enables the DR member devices to detect a peer interface down event
more quickly than the long DRCP timeout timer. However this benefit is at the expense of bandwidth
and system resources.
Keepalive and failover mechanism
For the secondary DR device to monitor the state of the primary device, you must establish a Layer
3 keepalive link between the DR member devices.
The DR member devices periodically send keepalive packets over the keepalive link. If a DR
member device has not received keepalive packets from the peer when the keepalive timeout timer
expires, it determines that the keepalive link is down. When both the keepalive link and the IPL are
down, a DR member device acts depending on its role.
•
If its role is primary, the device retains its role as long as it has up DR interfaces. If all its DR
interfaces are down, its role becomes None.
•
If its role is secondary, the device takes over the primary role and retains the role as long as it
has up DR interfaces. If all its DR interfaces are down, its role becomes None.
A device with the None role cannot send or receive keepalive packets. Its keepalive link stays in the
down state.
If the keepalive link is down while the IPL is up, the DR member devices prompt you to check for
keepalive link issues.
If the keepalive link is up while the IPL is down, the DR member devices elect a primary device based
on the information in the keepalive packets.