IOS XE on ASR1000 provides two forms of redundancy. First one is well-known hardware redundancy available in ASR1006 where two RP’s and ESP’s can be installed. On other platforms software redundancy and ISSU can be configured. Because IOS XE is in fact just one of a Linux processes running on the platform while system is booting up no one but two instances of iosd are executed in background, but only one is active. Both processes are running on same Route Processor. Standby IOS process can be switched to in the event of an IOS failure, and can also be used to upgrade sub-package software in some scenarios as the standby IOS process in an ISSU upgrade.
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