ning CatOS, an EtherChannel is called a channel, while on a switch running IOS, an EtherChannel is called a port channel interface. The command to configure an EtherChannel on CatOS is set port channel, and the commands to view channels include show port channel and show channel. EtherChan- nels on IOS switches are actually virtual interfaces, and they are referenced like any other interfaces (for example, interface port-channel 0 or int poo). IOS switch CatOS switch Port channel interface EtherChannel Channel Po0, Po1, etc. Figure 7-1. EtherChannel on IOS and CatOS There is another terminology problem that can be a source of many headaches for network administrators. While a group of physical Ethernet links bonded together is called an EtherChannel in Cisco parlance, Solaris refers to the same configuration as a trunk. Of course, in the Cisco world the term "trunk" refers to something com- pletely different: a link that labels frames with VLAN information SO that multiple VLANs can traverse it. Figure 7-2 shows how Cisco and Solaris label the same link differently. This can cause quite a bit of confusion, and result in some amusing conversations when both sides fail to understand the differences in terminology. IOS switch EtherChannel Solaris Port channel interface Trunk Po0, Po1, etc. Trunk Figure 7-2. Cisco and Solaris terminology regarding EtherChannels Load Balancing As stated earlier, EtherChannel by default does not truly provide the aggregate speed of the included physical links. EtherChannel gives the perceived speed of the com- bined links by passing certain packets through certain physical links. By default, the physical link used for each packet is determined by the packet's destination MAC address. The algorithm used is Cisco-proprietary, but it is deterministic, in that Chapter 7: EtherChannel packets with the same destination MAC address will always travel over the same physical link. This ensures that packets sent to a single destination MAC address never arrive out of order. The hashing algorithm