The main difference between capturing packets using Network TAP and SPAN ports.
Port Mirroring (also known as SPAN)
Network Tap (also known as Replication Tap, Aggregation Tap, Active Tap, Copper Tap, Ethernet Tap, etc.) TAP (Terminal Access Point) is a fully passive hardware device, which can passively capture traffic on a network. It is commonly used to monitor the traffic between two points in the network. If the network between these two points consists of a physical cable, a network TAP may be the best way to capture traffic.
Before explaining the differences between the two solutions(Port Mirror and Network Tap), it is important to understand how the Ethernet works. At 100Mbit and above, hosts usually speak in full duplex, meaning that one host can send(Tx) and receive(Rx) simultaneously. This means that on a 100 Mbit cable connected to one host, the total amount of the network traffic that one host can send/receive(Tx/Rx)) is 2 × 100 Mbit = 200 Mbit.
The Port mirroring is active packet replication, which means that the network device is physically responsible for copying the packet to the mirrored port.
Capturing Traffic: TAP vs SPAN
When monitoring network traffic, if you don't want to operationalize support directly while a user is processing a transaction, you have two main options. In the following article, we'll give an overview of TAP (Test Access Point) and SPAN (Switch Port Analyzer). For a deeper analysis, packet inspection expert Timo'Neill has several articles at lovemytool.com that go into great detail, but here, we'll take a more general approach.
SPAN
Port mirroring is a method of monitoring network traffic by forwarding a copy of each incoming and/or outgoing packet from one or more ports (or VLans) of a switch to another port connected to a network traffic analyzer. Spans are often used in simpler systems to monitor multiple sites simultaneously. The exact number of network transmissions it is able to monitor depends on where the SPAN is installed relative to the data center equipment. You'll probably find what you're looking for, but it's easy to find yourself with too much data. For example, it is possible to find multiple copies of the same data across an entire VLAN. This makes LAN troubleshooting more difficult, and also affects the speed of switch cpus or affects the Ethernet through placement detection. Basically, the more spans, the more likely it is to lose packets. Compared to taps, spans can be managed remotely, which means less time is spent changing configurations, but network engineers are still required.
SPAN ports are not a passive technology, as some claim, because they can have other measurable effects on network traffic, including:
- Time to change frame interaction
- Dropping packets due to excessive lookups
- Corrupted packets are dropped without notice, hindering the analysis
Therefore, SPAN ports are more suitable for situations where dropping packets does not affect the analysis, or where cost is considered.
TAP
In contrast, taps need to spend money on hardware up front, but they don't require much setup. Indeed, since they are passive, they can be connected and disconnected from the network without affecting it. Taps are hardware devices that provide a way to access data flowing through a computer network and are commonly used for network security and performance monitoring purposes. The monitored traffic is called "pass-through" traffic and the port used for monitoring is called "monitoring port". To probe the network more clearly, taps can be placed between routers and switches.
Because TAP does not affect packets, it can be viewed as a truly passive way to view network traffic.
There are basically three types of TAP solutions:
- Network splitter (1 : 1)
- Aggregate TAP (multi : 1)
- Regeneration TAP (1 : multi)
TAP replicates traffic to a single passive monitoring tool, or to a high-density network packet relay device, and serves multiple (often multiple) QOS testing tools, network monitoring tools, and network sniffer tools such as wireshark.
In addition, TAP types vary depending on the type of cable, including fiber TAP and gigabit copper TAP, both operating in essentially the same way by offloading part of the signal to the network traffic analyzer, while the main model continues to transmit without interruption. For the fiber TAP, it is to split the beam in two, while in the copper cable system, it is to replicate the electrical signal.
Comparing the TAP and SPAN
First, the SPAN port is not suitable for a full-duplex 1G link, and even when below its maximum capacity, it quickly drops packets because it is overburdened, or simply because the switch prioritizates regular port-to-port dates over SPAN port data. Unlike network taps, SPAN ports filter out physical layer errors, making some types of analysis more difficult, and as we have seen, incorrect increment times and changed frames can cause other problems. On the other hand, TAP can operate a full-duplex 1G link.
TAP can also perform complete packet capture and perform in-depth packet inspection for protocols, violations, intrusions, etc. Thus, TAP data can be used as evidence in court, whereas SPAN port data cannot.
Security is another aspect where there are differences between the two techniques. SPAN ports are usually configured for one-way communication, but they can also receive communication in some cases, causing serious vulnerabilities. In contrast, TAP is not addressable and does not have an IP address, so it cannot be hacked.
SPAN ports typically do not pass VLAN tags, which can make it difficult to detect VLAN failures, but taps cannot see the entire VLAN network at once. If aggregated taps are not used, the TAP will not provide the same trace for both channels, but care must be taken with overage detection. There are aggregate taps, such as Booster for Profitap, that aggregate eight 10/100/1G ports in a 1G-10G output.
Booster is able to enter packets by inserting VLAN tags. In this way, the source port information of each packet will be forwarded to the analyzer.
SPAN ports are still a tool that network administrators will use, but if speed and reliable access to all network data are critical, TAP is the better choice. When deciding which approach to take, SPAN ports are more suitable for networks with low utilization, since lost packets do not affect the analysis or are optional in cases where cost is a concern. However, on networks with high traffic, TAP's capacity, security, and reliability will provide full visibility into the traffic on your network without the fear of packet loss or filtering out physical layer errors.
○ Fully visible
○ Replicate all traffic (all packets of all sizes and types)
○ Passive, non-intrusive (doesn't change data)
○ In series, no switch ports are used to replicate full-duplex traffic in harnesses Easy setup (plug and play)
○ Not vulnerable to hackers (invisible, isolated monitoring device from network, no IP/MAC address)
○ Scalable
○ Suitable for any situation
○ Partial visibility
○ Not copying all traffic (dropping certain sizes and types of packets)
○ Non-passive (changing packet timing, increasing latency)
○ Use switch port (each SPAN port uses a switch port)
○ Unable to handle full-duplex communication (packets dropped when overloaded, may also interfere with primary switch operation)
○ Engineers need to configure
○ Unsafe (Monitoring system is part of the network, potential security problems)
○ Not scalable
○ Feasible only under certain circumstances
You may be interesting the related article: How to Capture Network Traffic? Network Tap vs Port Mirror
Post time: Jun-09-2025