Switch & Router ARP request

[tanbc3323]

Hi,

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

[pkhatri]

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

[arvindchari]

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

[tanbc3323]

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 ?

[pkhatri]

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

[tanbc3323]

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 ?

[schmidta]

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.