I am in the process of understanding a bit deeper the functionality of bridges however i am a bit confused on the matter.

I still dont understand why would you pick a bridge over a router when you bridge two different subnets.

Assuming you gave:

No default gateways on either networks.

Even if you use a bridge here, the hosts inside network_a wont be able to communicate with hosts on network_b. You need a router to route the layer3. If so, then you will just use the router to connect the network without the need of the Bridge.

  1. How/Why would you use a bridge to connect two different subnets assuming you gave no gateway?

  2. That been said, how does software bridging works without having default gateways?

  • 1
    "I still dont understand why would you pick a bridge over a router when you bridge two different subnets." You do not do that because you cannot communicate between different networks without a router. Routers route packets between networks, but bridges bridge frames on the same network. A host trying to send something to a different network will send the frame to its configured gateway (router), so the traffic from one network will not reach the host on a different network on the same bridged network.
    – Ron Maupin
    Sep 10 '20 at 21:39
  • I removed the off-topic host/server/VM questions. You can ask those on other SE sites.
    – Ron Maupin
    Sep 10 '20 at 21:40
  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can post and accept your own answer.
    – Ron Maupin
    Dec 17 '20 at 21:41

Bridging is data link layer connectivity (L2), routing is network layer connectivity (L3). Both accomplish different things.

Bridging the networks and accomplishes nothing. Even though both IP networks share the same data link layer they won't talk to each other. An IP sender checks whether the destination shares its subnet - if it does, the packet is sent directly by L2 frame; if it doesn't a gateway is required.

As a rule of thumb, L2 connectivity allows for quick and simple building of (unstructured) networks. L3 connectivity uses logical addressing, allowing the creation of arbitrarily large, structured networks.

  • ok so when you use a bridge the networks must be in the same subnet right?
    – giomanda
    Sep 18 '20 at 9:28
  • For IP connectivity, yes - unless you use a router.
    – Zac67
    Sep 18 '20 at 9:45

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