5

I just learned networking and according to a wiki article on broadcast radiation prevention, it says:

  • Filtering broadcasts by Layer 3 equipment, typically routers (and even switches that employ advanced filtering called brouters).

But I do not understand how exactly routers resolves broadcast storm problem. Any explanation in detail?

  • Heat sinks on the ASIC's made of lead – John Jensen Dec 18 '14 at 0:16
7

But I do not understand how exactly routers resolves broadcast storm problem. Any explanation in detail?

When a router receives a packet, it gets inspected, then forwarded out the appropriate interface or it gets dropped. When a router receives a broadcast packet, it drops it (excluding directed-broadcasts, dhcp, etc).

When a switch receives a frame, it either forwards it on to a known interface or floods it out all of its ports if it doesn't know where to go. When a broadcast frame comes along, it get's flooded out all interfaces. Every machine in your segment sees it. Excessive amounts of these constitute a storm.

The most common way for a broadcast storm to happen is from a switching loop. If you somehow get a switching loop on your network, these broadcasts will perpetually send this data back and forth forever, or until you remove the loop. This will cause data to hit every machine on your segment. This can cause your network to stop.

When you have a router in between multiple layer 2 segments, each is inherently protected from the other. Remember, a router won't forward on broadcasts.

For instance:

+-----+    +------+    +-----+
|LAN 1|----|ROUTER|----|LAN 2|
+-----+    +------+    +-----+

LAN 1 can be all sorts of messed up, and LAN 2 will be none the wiser because ROUTER won't forward LAN 1 broadcast packets on to anyone.

  • How does router know whether this packet is a broadcast packet or not? – CSnerd Dec 17 '14 at 22:11
  • 2
    Because a broadcast packet will have the destination frame address of FF:FF:FF:FF:FF:FF, which will not be the layer 2 address a router is listening for. – Ryan Foley Dec 17 '14 at 22:24
-1

Yes A router stops broadcast domain is correct statement. I will give you answer in simple words. First of all broadcast means sending a single packet to all the devices rather than a particular device which to be sent in that net work.The ports in switch are of separate collision and broadcast domain. So whenever a packet is sent, like hub the switch transfers the packet to each and every port which results in network bandwidth efficiency. So between two networks a layer 3 device which is called router is place to stop forwarding the broadcast. Instead it checks the packet, refers the address and send to the concerned device to which it has to be sent. A router forward broadcast domain at certain point when it has no IP address and forward Broadcast to DHCP server in order to get assigned of an IP address.

  • 1
    You didn't really answer the question of how does a router stop broadcast storms. You may want to revise your answer. – Ron Trunk Aug 4 '16 at 17:06

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.