Huawei NetEngine80E Configuration Manual - Reliability page 375

HUAWEI NetEngine80E/40E Router
Configuration Guide - Reliability
GR
In IETF, protocols related to Internet Protocol/Multiprotocol Label Switching (IP/MPLS) such
as Open Shortest Path First (OSPF), Intermediate System-Intermediate System (IS-IS), Border
Gateway Protocol (BGP), Label Distribution Protocol (LDP), and Resource Reservation
Protocol (RSVP) are extended to ensure that the forwarding is not interrupted when the system
is restarted. This reduces the flapping of the protocols at the control plane when the system
performs the AMB/SMB switchover. This series of standards is called GR extension to each
protocol. Currently, GR has been widely applied to the AMB/SMB switchover and system
upgrade.
The system can perform GR on the condition that the forwarding plane is separated from control
plane. That is, the router has a main board and an Interface board, and the Interface board
forwards packets. When the system restarts the protocol or performs AMB/SMB switchover,
the interface board is not reset. The interface board continues forwarding packets; thus, packets
can be forwarded in the entire system without interruption. The prerequisite to uninterrupted
forwarding in the system is that the network topology and interface status do not change in the
GR period; otherwise, the system exits from the GR and the forwarding is interrupted.
The concepts related to the GR are as follows:
l
l
The administrator and the fault can trigger the restart and AMB/SMB switchover of the GR
Restarter.
The following describes the GR process during the AMB/SMB switchover.
1.
Issue 02 (2011-09-10)
Roles
– GR Restarter: indicates a router on which the routing protocol is enabled with the GR
capability. The router has dual main boards, and is capable of notifying the neighbor to
maintain the adjacency during AMB/SMB switchover.
– GR Helper: indicates the neighbor of the GR Restarter. The GR Helper should be able
to identify the GR signaling, maintain the adjacency with the GR Restarter during the
AMB/SMB switchover, and help the GR Restarter to restore the network topology.
NOTE
The GR Restarter and the GR Helper interact with each other. When the GR Helper is enabled with
the GR capability, the GR Restarter and the GR Helper can interchange.
Session and timer
– GR session: indicates the session that has the GR capability. Through the session, the
GR Restarter and the GR Helper negotiate the GR capability.
– GR time: indicates the time of maintaining the undeleted routing information after the
GR Helper finds that the GR Restarter becomes Down. The GR time can be regarded
as the period between the start and end of the GR session.
NOTE
The mechanisms of implementing GR in each protocol are different. For the detailed value of the
GR time, refer to the HUAWEI NetEngine80E/40E Router Configuration Guide - IP Routing and
HUAWEI NetEngine80E/40E Router Configuration Guide - MPLS.
NOTE
If the network topology or the interface status changes, the system exits from GR. In the following
description, it is assumed that the network topology and interface status do not change.
The GR Restarter and the GR Helper negotiate the GR capability and establish a session.
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