Cisco Cisco Packet Data Gateway (PDG) Fehlerbehebungsanleitung
Interchassis Session Recovery
Overview ▀
Cisco ASR 5000 Series Enhanced Feature Configuration Guide ▄
OL-22982-01
AAA Monitor
AAA servers are monitored using the authentication probe mechanism. AAA servers are considered up if the
authentication-probe receives a valid response. AAA servers are considered down when the max-retries count specified
in the configuration of the AAA server has been reached. The service-redundancy protocol will initiate a switchover
when none of the configured AAA servers responds to an authentication probe. AAA probing is only be performed on
the active chassis.
authentication-probe receives a valid response. AAA servers are considered down when the max-retries count specified
in the configuration of the AAA server has been reached. The service-redundancy protocol will initiate a switchover
when none of the configured AAA servers responds to an authentication probe. AAA probing is only be performed on
the active chassis.
Important:
A switchover event caused by a AAA monitoring failure is non-revertible. If the newly active chassis
fails to monitor the configured AAA servers it remains as the active chassis until either a manual switchover, or another
non-AAA failure event causes the system to switchover.
non-AAA failure event causes the system to switchover.
BGP Interaction
The service-redundancy protocol implements non-revertible switchover behavior by using a mechanism to adjust the
route modifier value for the advertised loopback/IP Pool routes. The initial value of the route modifier value is
determined by the chassis configured role and is initialized to a value that is higher than a normal operational value.
This ensures that in the event of an SRP link failure and a SRP task failure that the correct chassis is still preferred in the
routing domain. The Active and Standby chassis share the route modifier values they are currently using. When BGP
advertises the loopback and ip pool routes, it converts the route modifier into an autonomous systems (AS) path prepend
count. The Active chassis always has a lower route modifier, and thus prepends less to the AS-path attribute. This
causes the route to be preferred in the routing domain. In the event that communication on the redundancy link is lost,
and both chassis in the redundant pair are claiming to be Active. The previously Active chassis is still preferred since it
is advertising a smaller AS-path into the BGP routing domain. The route modifier is incremented as switchover events
occur. A threshold will be implemented to determine when the route modifier should be reset to its initial value to avoid
rollover.
route modifier value for the advertised loopback/IP Pool routes. The initial value of the route modifier value is
determined by the chassis configured role and is initialized to a value that is higher than a normal operational value.
This ensures that in the event of an SRP link failure and a SRP task failure that the correct chassis is still preferred in the
routing domain. The Active and Standby chassis share the route modifier values they are currently using. When BGP
advertises the loopback and ip pool routes, it converts the route modifier into an autonomous systems (AS) path prepend
count. The Active chassis always has a lower route modifier, and thus prepends less to the AS-path attribute. This
causes the route to be preferred in the routing domain. In the event that communication on the redundancy link is lost,
and both chassis in the redundant pair are claiming to be Active. The previously Active chassis is still preferred since it
is advertising a smaller AS-path into the BGP routing domain. The route modifier is incremented as switchover events
occur. A threshold will be implemented to determine when the route modifier should be reset to its initial value to avoid
rollover.
Requirements
ICSR configurations require the following:
Two chassis configured for the same service types- The services must be bound on an srp activated loopback
interface.
Three contexts:
Redundancy - to configure the primary and backup chassis redundancy.
Source - AAA configuration the specified nas-ip-address must be the IP address of an interface bound
to an HA or any core network service configured within the same context.
Destination - to configure monitoring and routing to the PDN.
AAA RADIUS server
Border Gateway Protocol (BGP) - ICSR uses the route modifier to determine the chassis priority.