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### Instruction:
XLNC-4-LINUX_LOOPBACK_ADDRESS_UPDATE_FAIL
### Response:
(Severity: 4), (Category: INFRA), (Description: XLNCd is responsible for keeping the networking stacks for IOS XR and Linux synchronized. Certain IOS XR interfaces only have L3 reachability, provided by having their IP addresses added to the Linux loopback device in the network namespace corresponding to the IOS XR VRF the address is configured in. This message indicates that XLNCd encountered an error while attempting to add or remove the specified address from the Linux loopback device. This may result traffic sourced from Linux applications being sent with the wrong source IP address, or received traffic destined to Linux applications not being processed correctly.), (Recommended Action: If the system is experiencing memory exhaustion, resolve other issues that may be causing this failure state, then attempt to recover by restarting XLNCd: <CLI> process restart xlncd </CLI> If the problem persists, inconsistencies between Linux and IOS XR can be observed by comparing the output of <CLI> show linux networking interfaces address-only </CLI> for the IOS XR VRF and <CLI> run ip netns exec <netns-name> ip addr show dev lo </CLI> IPv4 addresses that are missing from Linux can be added using <CLI> run ip netns exec <netns-name> ip addr add <ip> dev lo </CLI> Extra IPv4 addresses can be removed from Linux using <CLI> run ip netns exec <netns-name> ip addr del <ip> dev lo </CLI> IPv6 addresses that are missing from Linux can be added using <CLI> run ip netns exec <netns-name> ip -6 addr add <ip> dev lo </CLI> Extra IPv6 addresses can be removed from Linux using <CLI> run ip netns exec <netns-name> ip -6 addr del <ip> dev lo </CLI> Copy the error message exactly as it appears on the console or in the system log, call your Cisco technical support representative and provide the representative with the gathered information.)
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