Huawei Quidway NetEngine80E Configuration Manual page 292

HUAWEI NetEngine80E/40E Router
Configuration Guide - IP Routing
BFD for OSPF
By default, in broadcast networks, the interval for OSPF to send Hello packets is 10 seconds; in
NBMA networks, the interval for sending Hello packets is 30 seconds, and the period for
advertising that the neighbor is Down is four times the interval for sending Hello packets. If the
router does not receive the Hello packet from the neighbor before the neighboring router becomes
invalid, it deletes the neighbor. That is, the router detects the neighbor faults in seconds. This
leads to the loss of a large number of packets in a high-speed network.
To solve the preceding problem in the current detection mechanism, Bidirectional Forwarding
Detection (BFD) is developed. BFD can implement detection at the millisecond level. Instead
of replacing the Hello mechanism of OSPF, BFD works with OSPF to fast detect the adjacency
fault. BFD is used to notify OSPF of recalculating routes. This can correctly guide the packet
forwarding.
Routing Management (RM) module exchanges routing information with the BFD module.
Through RM, OSPF notifies BFD of dynamically setting up or deleting BFD sessions. The Event
message of BFD is delivered to OSPF through RM.
The process of establishing and deleting a BFD session is as follows:
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OSPF supports dynamically establishing or deleting a BFD session on broadcast, P2P, P2MP,
and NBMA links.
Configure BFD according to the actual network environment. If time parameters are set
incorrectly, network flapping occurs.
OSPF-BGP
When a new router is connected to the network, or a router restarts, the network traffic may be
lost during BGP convergence. This is because the IGP route convergence is quicker than the
BGP route convergence.
If the backup link exists, OSPF-BGP linkage makes a router that restarts or a router that is
connected to the network start the stub router timer during the OSPF-BGP linkage. During the
set linkage period, the router acts as the stub router by increasing the metrics of the links in the
LSA generated by the router to 65535. Other OSPF devices are notified of not using the stub
router to forward data. This ensures that the router is not used as the spanned router. This avoids
traffic loss during traffic switchback because route convergence speed is slower than that of
OSPF.
GTSM
The Generalized TTL Security Mechanism (GTSM) refers to the generic TTL security protection
mechanism. GTSM protects services of the upper layer over the IP layer by checking whether
Issue 02 (2014-09-30)
Process of establishing a BFD session: If BFD feature is globally configured, BFD is
enabled on an interface or a process, and the status of the OSPF neighbor is Full, OSPF
uses RM to notify the BFD module of establishing the BFD session and negotiate related
parameters of BFD.
Process of deleting a BFD session: When BFD detects a link fault, BFD generates a Down
event and notifies the upper protocol of the fault through RM. OSPF then responds to the
event and immediately deletes the adjacency relationship on the link. At this time, the status
of the neighbor is not Full. This does not meet the requirements of establishing a BFD
session. OSPF then uses RM to notify the BFD module of deleting the BFD session.
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5 OSPF Configuration
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