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A bridge connects two LANs within a single domain, using Media Access Control addresses to determine destinations. Bridge traffic is non-routable, meaning data cannot move outside of the joined networks, or domain. Now, let's dissect the difference between a bridge and router.
A router also connects two LANs and moves traffic via IP addresses. Routers have the intelligence to determine the next network point if the address is not within its managed pool of endpoints. Routers understand the state of the connected networks and where to forward non-local packets.
Features of a bridge
Bridges are essentially repeaters. They send any data from one network to another. A simple bridge will have two ports -- in and out -- and will only connect two networks. A multiport bridge would provide bridging between multiple networks. Bridges use filtering tables to decide if a frame should be forwarded or dropped, based on whether it is included in the pool of connected clients.
Features of a router
Unlike a bridge, if a router receives a packet that is not destined for a connected client, it will forward that packet onward. Routers depend on a routing table in order to know the next destination if it is outside the pool of addresses that the router is maintaining.
A typical router will have a WAN interface along with a LAN interface. The WAN connection is for all traffic outside of the router's pool, and the LAN connection is for local clients. A router is located at any gateway -- where one network meets another -- including each point of presence on the internet. Some consumer routers combine a network switch as well.
Can I replace a bridge with a router?
Because both bridges and routers connect networks together, they can be interchangeable to a degree. A router could replace a bridge, connecting two networks. But it does not make sense to replace a router with a bridge because routers can forward non-local traffic and bridges will simply drop traffic for addresses not in their local tables.
Learn about the differences between a bridge and switch
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