How to learn packet flow through routers and switches
Posted on 2010-08-18
Can anyone recommend a good source to learn the path a packet takes trough routers and switches?
I am looking for some material that goes step by step from the source through the switch, vlan interface, the router and finally the end point . Stopping at each step along the way to explain exactly what happens.
For example why does a router have an arp cache of ip addresses to macs if it is going to send the packet to a different layer 3 switch that has vlan interfaces. Isn't the layer 3 switch capable of accepting the packets, routing the packet to the correct vlan and then sending arp messages to find the mac address associated with the ip address?
Another example is when you do a "sh ip arp 22.214.171.124" you get mac addresss aa.aa.aa.aa.aa.aa and 126.96.36.199. is assigned to gi1/1. But when I "sh ip route 188.8.131.52" it shows directly connected via gi1/1 so do you even need the mac address if the routing table shows as directly connected?
I am thinking about going back and rereading Lammle CCNA but I read that several times and at the time I thought that I got it. But when I get on routers and switches and start trying to visualize being the packets I get confused.
I am not really curious about the inner workings of these devices past the point of being able to confidently follow the packet from source to destination. I would also like to learn proper network design and troubleshooting.