Understanding Hitless Failover Support—Modular Switches Only
ExtremeWare XOS 11.3 Concepts Guide
77
Platform Support for Hitless Failover
Table 12 lists when each modular platform introduced support for hitless failover for a specific protocol.
As described in Table 11, not all protocols support hitless failover.
Open Shortest Path
First (OSPF)
If you configure OSPF graceful restart, there is no traffic interruption. However,
after OSPF comes up after restart, OSPF re-establishes sessions with its
neighbors and relearns Link State Advertisements (LSAs) from all of the
neighbors. This causes an increase in control traffic onto the network.
If you do not configure graceful restart, the route manager deletes all OSPF
routes 1 second after the failover occurs, which results in a traffic interruption
in addition to the increased control traffic.
Yes
Open Shortest Path
First v3 (OSPFv3)
OSPFv3 does not support graceful restart, so the route manager deletes all
OSPFv3 routes 1 second after the failover occurs. This results in a traffic
interruption.
In addition, after OSPFv3 comes up on the new primary MSM, it relearns the
routes from its neighbors. This causes an increase in control traffic onto the
network.
No
Border Gateway
Protocol (BGP)
BGP does not support graceful restart, so the route manager deletes all BGP
routes 1 second after the failover occurs. This results in a traffic interruption.
In addition, after BGP comes up on the new primary MSM, it re-establish
sessions with its neighbors and relearns routes from all of them. This causes
an increase in control traffic onto the network.
No
Power over Ethernet
(PoE)
The PoE configuration is checkpointed to the backup MSM. This ensures that
if the backup takes over, all ports currently powered stay powered after the
failover and the configured power policies are still in place.
This behavior is applicable only on the BlackDiamond 8800 family of switches.
Yes
Network Login 802.1x Authentication
Authenticated clients continue to remain authenticated after failover. However,
1 second after failover, all authenticated clients are forced to re-authenticate
themselves.
Information about unauthenticated clients is not checkpointed across MSMs so
any such clients that were in the process of being authenticated at the instant
of failover must go through the authentication process again from the
beginning after failover.
Yes
Network Login
Continued
MAC-Based Authentication
Authenticated clients continue to remain authenticated after failover so the
failover is transparent to them. Information about unauthenticated clients is
not checkpointed across MSMs so any such clients that were in the process of
being authenticated at the instant of failover must go through the
authentication process again from the beginning after failover.
In the case of MAC-Based authentication, the authentication process is very
short with only a single packet being sent to the switch so it is expected to be
transparent to the client stations.
Yes
Network Login
Continued
Web-Based Authentication
Web-based Netlogin users continue to be authenticated after a failover.
Yes
Table 11: Protocol support for hitless failover (Continued)
Protocol Behavior Hitless
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