Difference Between Cisco Bridge Group and Cisco Bridge Domain (With Table)

Bridging is an important process in all network operating systems. It enables the communication between interfaces that are connected to the network switch. Bridge group and bridge domain are two concepts that are related to this. The key differences between them are important to understand for carrying out various bridging activities.

Cisco Bridge-Group vs Cisco Bridge Domain

The difference between Cisco bridge group and Cisco bridge domain lies in the functions that they are supposed to perform. The function of Cisco bridge group is to organize configuration by grouping all the physical interfaces into one logical group. On the other hand, bridge domain represents a Layer 2 broadcast domain that carries out forwarding and bridging processes on this tier.

Cisco bridge group is a virtual interface that is used to group one or more interfaces together. In doing so, a group of switched interfaces is created. Workstations as well as other endpoint devices can then be attached directly to the interfaces that are a part of the bridge group. A third-party physical switch is not needed anymore.

Cisco bridge domain is something that defines a unique Layer 2 MAC address space. It provides Layer 2 forwarding inside a fabric along with a Layer 2 boundary. For this purpose, it must be connected to a technology called the VRF (Virtual routing and forwarding). Moreover, it must be associated with at least one subnet.

Comparison Table Between Cisco Bridge Group and Cisco Bridge Domain

Parameters of ComparisonCisco bridge groupCisco bridge domain
FunctionThe function of Cisco bridge group is to organize configuration by grouping interfaces into one logical group.The function of Cisco bridge domain is to carry out forwarding and bridging processes.
NatureCisco bridge group is a virtual interface.Cisco bridge domain is the space that defines a broadcast domain.
FrameworkCisco bridge-group consists of BVI (Bridge-Group Virtual Interface).Cisco bridge domain consists of BDI (Bridge Domain Interface).
LayerBridge groups perform only at Layer 2 and are not ideal for Layer 3 switchingBridge domains exist as a Layer 2 domain but facilitate its flow towards a Layer 3 routed network.
Operating SystemCisco bridge group can be used for platforms that run Cisco IOS.Cisco bridge domain can be used for platforms that run Cisco IOS-XE.

What is Cisco Bridge Group?

Bridge group is something that generally creates segmented switching domains. Its function is to organize a configuration by pooling several interfaces into one logical group. In each bridge group, traffic is set within the boundaries of the hosts. However, this process cannot take place between two bridge groups. A switch is used to forward traffic among these hosts. It also restricts broadcast and flooding.

The advantage of using a bridge group is that it reduces network congestion for the smooth functioning of the operating system. It also provides additional security at the point when traffic is segmented to different areas of a network. An important aspect includes the existence of bridge groups in wireless networks. Here, the groups are configured on wireless access points and bridges. This is done to carry out transfers between wireless media and a wired one.

Each bridge is supposed to have one bridge group per VLAN. This facilitates the bidirectional communication that takes place between two parties in the operating system. As the number of VLANs increases, so does the number of bridge groups. Nonetheless, a router does not allow the configuration of Layer 3 interfaces that exist in a single broadcast domain. This can be achieved by using a BVI that facilitates a routable logical interface. 

What is Cisco Bridge Domain?

In simple terms, a bridge domain is something that makes it possible to define a broadcast domain that is contained within a bridging device. It is a substitute for 802.1D bridge groups as well as 802.1Q VLAN bridging. The purpose of a bridge domain is to specify the broadcast domain number. The frame of the service instance must be made available in this space.

A certain method is required for bridge domains to catch hold of MAC addresses. This is carried out with the help of a learning domain. A learning domain is something that facilitates the forwarding of a MAC database. Each bridge domain must have one learning domain. However, it is also possible for several learning domains to be part of one of them. All bridge domains also contain numerous IFLs that have similar characteristics when it comes to flooding, filtering, and forwarding.

One or more bridge groups can be grouped within a single instance or a single virtual switch. Some series of routers allow this within multiple virtual switches. In such a case, each virtual switch operates independently on the router. These virtual switches also isolate a LAN segment which allows them to infiltrate a different Layer 2 network.

Main Differences Between Cisco Bridge Group and Cisco Bridge Domain

  1. The function of Cisco bridge group is to organize configuration by grouping interfaces into one logical group whereas the function of Cisco bridge domain is to carry out forwarding and bridging processes.
  2. Cisco bridge group is a virtual interface whereas Cisco bridge domain is a space that defines a broadcast domain.
  3. Cisco bridge-group consists of BVI whereas Cisco bridge domain consists of BDI.
  4. Cisco bridge-group functions only involve Layer 2 processes while Cisco bridge domain functions involve Layer 2 as well as Layer 3 processes.
  5. Cisco bridge group can be used for platforms that can run Cisco IOS whereas Cisco bridge domain can be used on platforms for Cisco IOS-XE.

Conclusion

Understanding the difference between Cisco bridge group and Cisco bridge domain can be quite an arduous task given the fact that there is so much technical jargon involved. However, in simple words, the only notable and specific function that Cisco bridge group is made to perform is organizing configurations. Bridge group pools interfaces into one single logical group. This minimizes the chances of traffic congestion in an operating system.

On the other hand, bridge domains perform several functions. The main purpose of having them in an operating system is to facilitate the processes of forwarding and bridging. These processes are carried out between Layer 2 and Layer 3 routers, especially those that are made for Cisco IOS-XE operating system.

References

  1. https://ieeexplore.ieee.org/abstract/document/4463775/
  2. https://dl.acm.org/doi/pdf/10.17487/RFC2281
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