What is a difference between HUB and Switch with Port Mirroring?
Before reading this articles, you can check also following ones:
The Port Miroring feature was introduced on switches because of a fundamental difference that switches have with HUBs. When a HUB (see Figure 1) receives a packet on one port, the HUB sends out a copy of that packet on all ports except the one from where it was received (see below figure for illustration of HUB's work).
Figure 1. HUB
After a switch boots (see Figure 2), it starts to build up a Layer 2 forwarding table on the basis of the source MAC address of the different packets that the switch receives. After this a forwarding table is built, the switch forwards traffic that is destined for a MAC address directly to the corresponding port.
Figure 2. Switch
In a contrast to a HUB (which is a "dumb" repeater), managed switch with port mirroring (see Figure 3) feature is a "smart" repeater: it allows a configuration of which port(s) to monitor and where to send a copy of received packets. So, a copy of packets are sent to only one destination (analysis) port, while HUB sends copy of packets to all ports.
Figure 3. Switch with Port Mirroring
| HUB | Managed Switch with Port Mirroring | |
| Performance | acceptable for 3-5 devices, connected to a HUB | high performance |
| Voip packets prioritization (QOS) | Not supported. Quality of audio during a call may degrade if other computers, connected to a HUB, use intensively a network bandwidth, for example, download large file during an active call. | QOS is supported. Voip audio packets are given the higher priority than a general network traffic. Thus quality of audio is guaranteed. |
| Configuration | no configuration available | configuration via web or command line interface |
| Source ports for monitoring | all ports are permanently mirrored | administrator can specify which port or ports (or even VLAN) should be mirrored |
| Destination ports for monitoring | all ports on a HUB receive a copy of packets, which are transmitted through a HUB. | only single port can be configured to receive a copy of packets, which are sent through monitored ports. Althoug some of switches support multiple mirror sessions. |
Related articles: