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New Member

Switch & Router ARP request

Hi,

What is the diffirent between the Switch and Router regarding setting up the ARP table ? Please advice !

6 REPLIES
Purple

Re: Switch & Router ARP request

There is no real difference as far as ARP is concerned. You should not confuse this with the concept of MAC address learning. ARP is a layer-3 concept, used for mapping layer 3 addresses to layer 2 addresses. When a switch is L3-capable, it uses the same ARP mechanism as a router or a host. However, switches also learn MAC addresses on their switch ports, which is part of the function of switching. That is a completely different thing to ARP, though. The learned MAC addresses are used by switches to determine which ports to forward received frames out of.

Hope that helps - pls rate the post if it does.

Paresh

Bronze

Re: Switch & Router ARP request

In addition to Paresh's post another interesting detail you might want to look at is Proxy ARP

www.cisco.com/warp/public/105/5.html

The link above should give you a good head start to how proxy arp works

HTH

Please rate posts that help

Regards

Arvind

New Member

Re: Switch & Router ARP request

It means that L2 switch will flood the ARP request, and when reply comes back, the switch will register the MAC addres, which will also update the server's arp table. Am i right ?

How about the L3 or the router ? is it lessen the arp request from the server ?

Purple

Re: Switch & Router ARP request

That is correct - since the ARP will be broadcast, a reply to the ARP will enable the switch to associate the source MAC address of the ARP reply frame with the port it was received on.

In case of a router, broadcasts are confined to the interface since routers do not forward broadcasts. Therefore, a router will only learn the MAC address for a host when it itself wants to send a packet to that host.

Hope that helps - pls rate the post if it does.

Paresh

New Member

Re: Switch & Router ARP request

Hi,

ARP broadcast flooding, is it a problem on large L2 networks ? How we can slove the ARP broadcast flooding problem ? with separate vlan can solve ? or must using router ?

New Member

Re: Switch & Router ARP request

Hi,

it is a good design to keep the broadcast domain small,

because every PC must execute a broadcast and this can reduce the performance.

When you use vlans you need L3 components (Switch or Router) to transmit packets between the vlans and (!)

ip-subnets.

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