Help with routing and switching addresses

jblake1986

I came across piece I dont understand while studying for the ccna

Host A sends a message to host B
Between host A and B there is 2 switches and a router

say host A has IP 111.111.111.111
Mac 00
B ip 222.222.222.222
Mac 01
Switch A 333.333.333.333
Mac 02
Switch B 444.444.444.444
Mac 03
Router 555.555.555.555
Mac 04

So if I sent a packet and it was going from host A to switch A then to Router how does the source and destination IP/Macs change

I thought the macs for source and destination were always 00 and 01. Do the Ip addresses change? such as between Switch A to Router destination 555.555.555.555 and source 333.333.333.333?

Any help is much appreciated

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capitanuionut

jblake1986 wrote: »

I came across piece I dont understand while studying for the ccna

Host A sends a message to host B
Between host A and B there is 2 switches and a router

say host A has IP 111.111.111.111
Mac 00
B ip 222.222.222.222
Mac 01
Switch A 333.333.333.333
Mac 02
Switch B 444.444.444.444
Mac 03
Router 555.555.555.555
Mac 04

So if I sent a packet and it was going from host A to switch A then to Router how does the source and destination IP/Macs change

I thought the macs for source and destination were always 00 and 01. Do the Ip addresses change? such as between Switch A to Router destination 555.555.555.555 and source 333.333.333.333?

Any help is much appreciated

For the hostA the destination mac address encapsulated in the frame will be the router's interface mac address, cause these is the default gateway.
The source mac address will be HostA's.

After reaching to the router, the packet is decapsulated, raised at layer 3, where the router reads the source and destionation ip addresses. After making a decision based on the routing table, the router reincapsulates the packet with a source mac address from the interface the packet will go out, and destionation mac address of the next hop in the network.

I hope i made myself clear enough and i provided corect informations.
Also the router has mac addresses for all it's interfaces.

At this point ip addresses do not change. You will learn when you arrive at NAT about this. But for know they don't change.

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