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New Member

Broadcast Domain

If I can have only one broadcast domain per port on a router but I have three different networks on that port, why is this still considered one broadcast domain? There are no vlan's!

2 REPLIES
New Member

Re: Broadcast Domain

Because remember, on a given ethernet segment, packets reach there destination via a hardware MAC address.

Just a quick review. You want to get to a destination. If that destination is not on your directly connected network, then the gateway, or default gateway is looked up for that destination. This gateway will be on your directly connected network. So now you get the MAC address for this gateway (via ARP) and you now send the packet to that MAC address.

If the destination had been on your directly connected network, then you would have just ARP'ed and gotten the MAC address for it (unless it was already in your ARP table/cache).

What this means is that on a given segment/network, packets are really transmitted via MAC address. So if you have 3 seperate networks on 1 single segment, those 3 broadcast addresses (lets say 192.168.1.255, 172.16.255.255, and 10.255.255.255) are all still being mapped to FF:FF:FF:FF:FF:FF. The only way to stop this, is making them seperate segments either by placing a router between networks, or by creating seperate vlans.

Brian

New Member

Re: Broadcast Domain

I must be overlooking something. Is this true for Router on a stick scenario with multiple assigned IP addresses on that interface?

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