Node Alias Overview

Node Alias is a feature that you can use to discover information about end systems on a per-port basis. As the packets from the end systems transit through a Node Alias-enabled port, its key attributes are captured in a database that can be queried (see CTRON Alias MIB). Enabling Node Alias on ports of interest provides a powerful troubleshooting tool for network administrators.


By default, Node Alias is disabled on all ports.


Currently, 100 packets per second per slot are admitted for snooping. Packets are dropped if the rate exceeds 100 pps.

Node Alias Database Information

Each entry in the Node Alias database consists of the following fields:
  • Incoming port
  • Source MAC address
  • Protocol address—Depending on the protocol type, this could be the IPv4/IPv6 source IP address, or the UDP source port in cases where the destination IP is broadcast, etc., the virtual router ID and Priority for VRRP.
  • Node Alias ID—A unique number that identifies an entry
  • Entry creation time

The database is capable of holding 8,192 entries per-slot. To avoid starvation among ports, each port is allowed to create only its share of entries in the database. The default maximum per port is 8,192 divided by the number of ports on the slot. For example, on a 64-port slot, this translates to 128 entries per port. You can modify the per-port maximum (configure nodealias ports [port_list |all] maxentries entries) up to the limit of 8,192.

As a result of snooping one frame, Node Alias may create additional entries to facilitate the searching based on finer details, such as protocol type. For example, when a BGP frame is received, two entries are created: one entry with protocol type IP, and another entry with protocol type BGP.

Node Alias also supports VMAN. For VMANs, itt includes the VMAN ID, instead of VLAN ID in the database.

If the ports are combined to form a LAG, Node Alias must be enabled on individual ports; enabling Node Alias on the master port does not automatically enable Node Alias on member ports.

Supported Protocols

Node Alias is enabled by default to capture all of the following supported protocols: IPv4, IPv6, OSPF, BGP, VRRP, DHCPS, DHCPC, BOOTPS, BOOTPC, UDP, BPDU, LLMNR, SSDP, and mDNS. You can selectively disable any of these protocols.


  • ARP is categorized under IP.
  • UDP entry is created when destination IP address is broadcast.
  • BPDU means STP and GVRP frames.