Huawei NetEngine80E Configuration Manual - Reliability page 23
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- Configuration manual - reliability (1432 pages) ,
- Configuration manual (1301 pages) ,
- Installation manual (169 pages)
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HUAWEI NetEngine80E/40E Router
Configuration Guide - Reliability
When LDP works in a mode of Downstream Unsolicited (DU) label distribution, ordered label
control and liberal label retention, a Label Switching Router (LSR) saves all label mapping
messages. Only the label mapping messages sent by the next hop corresponding to the
Forwarding Equivalence Class (FEC) can generate a label forwarding table.
With the preceding features, when a forwarding table is generated for mapping of liberal
retention label, this means that a bypass LSP is established. Normally, a packet is forwarded
through the primary LSP. When the outgoing interface of the primary LSP is Down, the packet
is forwarded along the bypass LSP. This ensures continuous traffic follow in the short period
before network convergence.
MPLS TE FRR
The MPLS TE FRR is a commonly used switchover technology to deal with a failure. The
solution is to create an end-to-end TE tunnel between Provider Edge (PE) devices and a bypass
Label Switched Path (LSP) for protecting a primary LSP. When the router detects that the
primary LSP is unavailable because of an intermediate node failure or link failure, the traffic is
switched to the bypass LSP.
In terms of principle, MPLS TE FRR can enable fast switchover to respond to link failures and
node failures between two PEs that serve as the start node and end node of a TE tunnel
respectively.
Nevertheless, MPLS TE FRR cannot deal with the failure of PEs that serves as the start node
and end node on a TE tunnel. When a PE fails, the traffic can resume by end-to-end route
convergence and LSP convergence. The time of convergence relates closely to the number of
routes of the MPLS VPN and the number of hops of the bearer network. Generally, the
convergence takes about 5s in typical networking, longer than 1s that is required for the end-to-
end traffic convergence when a node fails.
VPN FRR
Based on the VPN fast route switching technology, VPN FRR sets a switchover forwarding
entry that is destined for the primary PE and backup PE on a remote PE. With VPN FRR and
the technology of fast sense of PE failures, on an MPLS VPN where Costumer Edge (CE) devices
are dual-homed to PEs, the time of end-to-end service convergence is shortened and the time of
PE failure recovery cannot be affected by the number of private network routes. When a PE
node fails, the convergence of end-to-end service takes less than 1s.
On a PE device configured with VPN FRR, proper VPNv4 routes are selected by the matching
policy. For these routes, in addition to the routing information sent by the preferential next hop
(including forwarding prefix, inner tag, and selected outer LSP tunnel), information about the
inferior priority next hop (including forwarding prefix, inner tag, and selected outer LSP tunnel)
are also contained in the forwarded entry.
When preferential next hop node fails, through BFD and MPLS OAM, the PE detects that the
outer tunnel connecting the PE to the preferential node is unavailable. The PE sets a
corresponding flag in the LSP tunnel status table to indicates the outer LSP is unavailable and
delivers the flag to the forwarding engine. When the forwarding engine selects a forwarding
entry, it checks the LSP tunnel status corresponding to this forwarding entry. If the LSP tunnel
is unavailable, the engine uses the route of a inferior priority carried in this forwarding entry to
forward packets.
Issue 02 (2011-09-10)
Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
1 Reliability Overview
6
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