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DES-7200 Configuration Guide Chapter 3 MPLS Reliability Configuration
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The router with GR detection capability. Such router may not have dual management boards, but
it can detect that its neighbor is experiencing GR and help its neighbor to complete GR.
GR-Unaware router
The router without GR detection capability. It cannot detect that the neighboring router is
experiencing GR and cannot help the neighboring router to complete GR. This is generally
because the no GR feature is provided by the system software or the GR feature is disabled.
GR routers by role
During the process of router restart, routers can be classified into GR-Restarter router and
GR-Helper router according to router's role.
GR-Restarter router
GR-Restarter router must be a GR-Capable router, and the restart process is triggered by the
administrator or fault.
GR-Helper router
Neighbor of GR-Restarter, at least a GR-Aware router.
Working principle
To establish a GR-Capable LDP session, LDP GR must be enabled at both ends of the session.
During the process of establishing LDP session, if GR is not supported by any one end, then only
ordinary LDP session can be established. If the session initiator supports and enables LDP GR,
then FT Session TLV may be carried in the Initialization message.
When LDP session is established, if the acceptor receives Initialization message carrying FT
Session TLV, it will determine whether or not to carry FT Session TLV in the Initialization
message according to its own situation. If the acceptor supports and enables LDP GR, then it will
carry FT Session TLV in the Initialization message in order to establish a GR-Capable LDP
session. Otherwise, the acceptor will not carry FT Session TLV in the Initialization message in
order to establish an ordinary LDP session without GR capability. If the Initialization message
received by the acceptor doesn't carry FT Session TLV, then an ordinary LDP session without
GR capability will be established no matter it carries FT Session TLV in the Initialization message
or not. The following flowchart shows the process of establishing a session between two LDP
GR-Capable LSRs.