The stack has a primary IP address and subnetwork. These values are assigned using the configure vlan mgmt ipaddress command. There can also be static or default routes associated with the stack.
For each node in the stack, you can configure an alternate management IP address, subnetwork mask, and default gateway. The alternate IP address is restricted to being a member of the primary IP subnetwork that is configured on the management VLAN, and thus the alternate IP subnetwork must exactly match the primary IP management subnetwork. A subnetwork match is exact if the subnetwork portion of the IP addresses match exactly. For example, 10.11.12.1/24 and 10.11.12.2/24 are an exact subnetwork match (because both represent the subnet 10.11.12.0/24).
Standby nodes always install their configured alternate management IP address and gateway on the management interface. A standby node does not have the ability to verify whether the configured alternate IP address matches the primary management IP subnetwork of the stack.
The backup and master nodes have the ability to verify the configured alternate IP address. The master and backup nodes compare the primary IP subnetwork information to the alternate IP subnetwork. If there is a match, the backup node installs the primary IP management subnetwork‘s default routes and installs only the alternate management IP address (not the primary IP address). The master node installs both the configured management subnetwork with specific IP address and the alternate IP address. In this case, the alternate gateway is not used, expecting that primary management routes are configured or will be configured. In either case, if the alternate IP subnetwork does not match the configured management subnetwork, the alternate IP address is not installed on the management interface.
Each node in the stack normally installs its alternate IP address on the management subnetwork. When an ARP request for the alternate IP address is satisfied, the stackable switch supplies its factory-assigned MAC address and not the stack MAC address. Only the master node installs the primary IP address. An ARP request for the configured management IP address returns the configured stacking MAC address. Because of the above behavior, all nodes are reachable over their management ports even during a dual master condition. The VLAN used is the management VLAN (VID 4095) and is untagged.
The alternate gateway is only installed on a master or backup node when the primary management IP subnetwork is not configured. Once the primary IP subnetwork is installed, the alternate gateway is removed. The alternate gateway is always installed on a standby node.
If a dual master condition occurs because a stack has been severed, the alternate IP addresses and associated MAC addresses are unique, and it is possible to use telnet or ssh to reach any node. Any node on the segment with the incorrect master can then be used to reboot the entire stack segment into standby mode if you want to rejoin the stack segments later.
If a node is operating in stacking mode, the alternate management IP address configuration takes effect immediately.
Note
Only IPv4 alternate management IP addresses are supported in this release.To configure an alternate IP address and gateway, follow these steps.
Slot-1 Stack.6 # configure stacking slot 4 alternate-ip-address 10.127.4.139/24 10.127.4.254
Note
If you try to assign an alternate IP address and gateway to a node that is already configured with these parameters, an error message appears. To remove an existing configuration so you can change the alternate IP address and gateway, enter the unconfigure stacking {node-address node_address | slot slot_number} alternate-ip-address command.