Why cant routers forward arp packets?

1.Is it true that arp packets cannot be forwarded by routers since arp works at the link layer while routers work at the ip layer? why/ what does that mean?

2. what does it mean by the statement routers work at the ip layer?


pls help, thanks in advance

Yes it is true, just like routers do not forward on broadcast packets.

Read This for an excellent explanation of the OSI model.

thanks for the article, a few doubts though:
1.it is said that hubs forward all the traffic does that include arp packets as well, what about switches?

2.Also bridges work at the link layer, does that mean they can forward the arp or rarp packets?

1. Hubs are essentially signal repeaters, very primitive and I've never seen one in use aside from being in the middle of a very long stretch of ethernet cable. IIRC switches don't necessarily forward ARP/RARP packets, as they are the desination, but they will send out their own ARP/RARP packets through their trunks.

ie. you have 6 computers and 2 switches, 3 computers on each switch, and the switches are connected by one cable. Each computer tells the switch "I have X IP, and Y MAC", and each switch tells it's computers AND it's neighbour switch "I have these three IPs, this is my MAC". Once each switch has updated its neighbour switch the ARP tables will contain all 6 IP addresses and the MAC addresses of the interfaces that the traffic should be forwarded through.

Remember, layer 2 devices are only concerned with what they are directly connected to, and centers around MAC addresses.

2. I've never really paid attention to 'bridge' terminology, I believe they function more or less like switches in this context, but forwarding traffic between different network segments?

Repeaters (Layer 1) - Retime and resend packets. Just smart enough to need power.

Hubs (Layer 1) - Multi-port repeaters

Bridge (Layer 2) - Routes packets based on Layer 2 technologies

Switch (Layer 2) - Multi-port Bridge

The idea of the Bridge/Switch technology is that it limits "collision domains." I'm not going into the full detail here, look it up. It's one of the major limiting factors of a Hub network