Graceful Restart Communication Procedure - 3Com MSR 50 Series Configuration Manual

1958 C 105: GR O
HAPTER
Graceful Restart
communication
procedure
VERVIEW
GR Time
GR Time is the time taken for the GR Restarter and the GR Helper to establish a
session between them. Upon detection of the down state of a neighbor, the GR
Helper will preserve the topology and routing information sent from the GR
Restarter for a period as specified by the GR Time.
Configure a device as GR Restarter in a network. This device and its GR Helper
must support GR or be GR capable. Thus, when GR Restarter restarts, its GR
Helper can know its restart process.
n
In some cases, GR Restarter and GR Helper can replace with each other.
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If a router is to act as a Graceful Restarter, it must have the ability to preserve
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the routing information in the routing table (forwarding table). Routers that fail
to meet this can only act as a GR Helper.
The communication procedure between the GR Restarter and the GR Helper
works as follows:
1 A GR session is established between the GR Restarter and the GR Helper.
Figure 574 A GR session is established between the GR Restarter and the GR Helper
Router A
Router B
GR helper
As illustrated in
and Router D are the GR Helpers of Router A. A GR session is established between
the GR Restarter and the GR Helper.
2 GR Restarter restarting
Router D
GR helper
GR restarter
Router C
GR helper
GR capable GR session
Figure 574, Router A works as GR Restarter, Router B, Router C