By default, a device adds extra data to the end of a hello packet to make the packet the same size as the maximum length of PDU the device supports.
The padding applies to the following types of hello packets:
The padding consists of arbitrarily valued octets. A padded hello PDU indicates the largest PDU that the device can receive. Other ISs that receive a padded hello PDU from the device can, therefore, ensure that the IS-IS PDUs they send the device are lower than the maximum value available. Similarly, if the device receives a padded hello PDU from a neighbor IS, the device knows the maximum size PDU that can be sent to the neighbor.
When padding is enabled, the maximum length of a Hello PDU sent by the device is 1514 bytes.
If you need to disable hello padding, you can do so globally or on individual interfaces. Generally, you do not need to disable padding unless a link is experiencing slow performance. If you enable or disable padding on an interface, the interface setting overrides the global setting.