Netgear XCM8810 - 8800 SERIES 10-SLOT CHASSIS SWITCH ユーザーズマニュアル
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Chapter 24. OSPF
NETGEAR 8800 User Manual
Normally, support for opaque LSAs is autonegotiated between OSPF neighbors. In the event
that you experience interoperability problems, you can disable opaque LSAs across the
entire system using the following command:
that you experience interoperability problems, you can disable opaque LSAs across the
entire system using the following command:
disable ospf capability opaque-lsa
To re-enable opaque LSAs across the entire system, use the following command:
enable ospf capability opaque-lsa
If your network uses opaque LSAs, NETGEAR recommends that all routers on your OSPF
network support opaque LSAs. Routers that do not support opaque LSAs do not store or
flood them. At minimum a well interconnected subsection of your OSPF network must
support opaque LSAs to maintain reliability of their transmission.
network support opaque LSAs. Routers that do not support opaque LSAs do not store or
flood them. At minimum a well interconnected subsection of your OSPF network must
support opaque LSAs to maintain reliability of their transmission.
Graceful OSPF Restart
RFC 3623 describes a way for OSPF control functions to restart without disrupting traffic
forwarding. Without graceful restart, adjacent routers will assume that information previously
received from the restarting router is stale and will not be used to forward traffic to that router.
However, in many cases, two conditions exist that allow the router restarting OSPF to
continue to forward traffic correctly. The first condition is that forwarding can continue while
the control function is restarted. Most modern router system designs separate the forwarding
function from the control function so that traffic can still be forwarded independent of the state
of the OSPF function. Routes learned through OSPF remain in the routing table and packets
continue to be forwarded. The second condition required for graceful restart is that the
network remain stable during the restart period. If the network topology is not changing, the
current routing table remains correct. Often, networks can remain stable during the time for
restarting OSPF.
forwarding. Without graceful restart, adjacent routers will assume that information previously
received from the restarting router is stale and will not be used to forward traffic to that router.
However, in many cases, two conditions exist that allow the router restarting OSPF to
continue to forward traffic correctly. The first condition is that forwarding can continue while
the control function is restarted. Most modern router system designs separate the forwarding
function from the control function so that traffic can still be forwarded independent of the state
of the OSPF function. Routes learned through OSPF remain in the routing table and packets
continue to be forwarded. The second condition required for graceful restart is that the
network remain stable during the restart period. If the network topology is not changing, the
current routing table remains correct. Often, networks can remain stable during the time for
restarting OSPF.
Restarting and Helper Mode
Routers involved with graceful restart fill one of two roles: the restarting router or the helper
router. With graceful restart, the router that is restarting sends out Grace-LSAs informing its
neighbors that it is in graceful restart mode, how long the helper router should assist with the
restart (the grace period), and why the restart occurred. If the neighboring routers are
configured to help with the graceful restart (helper-mode), they will continue to advertise the
restarting router as if it was fully adjacent. Traffic continues to be routed as though the
restarting router is fully functional. If the network topology changes, the helper routers will
stop advertising the restarting router. The helper router will continue in helper mode until the
restarting router indicates successful termination of graceful restart, the Grace-LSAs expire,
or the network topology changes. A router can be configured for graceful restart, and for
helper-mode separately. A router can be a helper when its neighbor restarts, and can in turn
be helped by a neighbor if it restarts.
router. With graceful restart, the router that is restarting sends out Grace-LSAs informing its
neighbors that it is in graceful restart mode, how long the helper router should assist with the
restart (the grace period), and why the restart occurred. If the neighboring routers are
configured to help with the graceful restart (helper-mode), they will continue to advertise the
restarting router as if it was fully adjacent. Traffic continues to be routed as though the
restarting router is fully functional. If the network topology changes, the helper routers will
stop advertising the restarting router. The helper router will continue in helper mode until the
restarting router indicates successful termination of graceful restart, the Grace-LSAs expire,
or the network topology changes. A router can be configured for graceful restart, and for
helper-mode separately. A router can be a helper when its neighbor restarts, and can in turn
be helped by a neighbor if it restarts.
Planned and Unplanned Restarts
Two types of graceful restarts are defined: planned and unplanned. A planned restart would
occur if the software module for OSPF was upgraded, or if the router operator decided to
restart the OSPF control function for some reason. The router has advance warning, and is
occur if the software module for OSPF was upgraded, or if the router operator decided to
restart the OSPF control function for some reason. The router has advance warning, and is