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Considerations for using CDP

By default, CDP-compliant devices send CDPv2 advertisements. CDP-compliant devices send CDPv1 advertisements only when they receive CDPv1 advertisements. ONTAP supports only CDPv1. Therefore, when an ONTAP node sends CDPv1 advertisements, CDP-compliant neighboring devices send back CDPv1 advertisements.

You should consider the following information before enabling CDP on a node:

  • CDP is always enabled on cluster ports.

  • CDP is disabled, by default, on all non-cluster ports.

  • CDP is supported for all ports.

  • CDP advertisements are sent and received by ports that are in the up state.

  • CDP must be enabled on both the transmitting and receiving devices for sending and receiving CDP advertisements.

  • CDP advertisements are sent at regular intervals, and you can configure the time interval.

  • When IP addresses are changed for a LIF, the node sends the updated information in the next CDP advertisement.

    Note
    Sometimes when LIFs are changed on the node, the CDP information is not updated at the receiving device side (for example, a switch). If you encounter such a problem, you should configure the network interface of the node to the down status and then to the up status.

  • Only IPv4 addresses are advertised in CDP advertisements.

  • For physical network ports with VLANs, all of the LIFs configured on the VLANs on that port are advertised.

  • For physical ports that are part of an interface group, all of the IP addresses configured on that interface group are advertised on each physical port.

  • For an interface group that hosts VLANs, all of the LIFs configured on the interface group and the VLANs are advertised on each of the network ports.

  • For packets with MTU size equal to or greater than 1,500 bytes, only the number of LIFs that can fit into a 1500 MTU-sized packet is advertised.

  • Some Cisco switches always send CDP packets that are tagged on VLAN 1 if the native (default) VLAN of a trunk is anything other than 1.

    ONTAP only supports CDP packets that are untagged, both for sending and receiving. This results in storage platforms running ONTAP being visible to Cisco devices (using the show cdp neighbors command), and only the Cisco devices that send untagged CDP packets are visible to ONTAP.