- If the client is configured with a default gateway IP, then ARP is used to find out the gateway's hw address (i.e. the packet, in step 2, has the the gateway's mac address as the frame destination address. The destination IP address is still the same A.B.C.D) Also, if the client has no default gateway, proxy arp, on the router, could do the trick to figure out what the next hop is.
- RARP (reverse address resolution) would normally be used by a system that doesn't know its ip address then a RARP server will answer the system, so this rarp server kinda acts as a low level bootp server. - IP was designed for routing across networks, mac was basically design for one single flat network. Can you imagine a mac-only network for the whole internet? (50% of traffic would just be ARPing :) ) -mtm ----- Original Message ----- From: "Michael Ryan Byrd" <[EMAIL PROTECTED]> To: "BYU Unix Users Group" <[EMAIL PROTECTED]> Sent: Thursday, September 04, 2003 2:43 PM Subject: [uug] the big picture > I'm trying write down the big picture: > > Ok, so I fire up my browser and type www.google.com into the address line and > press enter: > > 1-my computer must first resolve www.google.com into an IP address. Some sort of > nslookup command is called which sends a nslookup command inside a TCP? packet > to the name server. Another TCP packet is received my computer with the result: > A.B.C.D > > 2-my computer looks at my subnet address and realizes that I am not on the same > network as google's A.B.C.D, so my computer sends out a HTTP GET request (again > encapsulated inside a TCP packet, which is encapsulated inside an IP packet, > which gets an Ethernet header and trailer which goes out ethernet card to the > local area network, through a switch to a router (gateway) to it's destination. > > 3-If I *was* on the same subnet as A.B.C.D my computer would have send out an > ARP packet asking for the MAC address of the host with IP address A.B.C.D. that > server would have replied with it's MAC address, AA:BB:CC:DD:EE:FF and then my > computer would have sent out a HTTP GET request inside a TCP inside a IP inside > an Ethernet packet addressed to AA:BB:CC:DD:EE:FF. > > Questions: > Is ARP used in scenerio #2? > When is the RARP protocol used? > Why do we have both IP and MAC addresses? Wouldn't just one of the two do > nicely? (I guess routers would have to route based on MAC address...) > > Ideas? > > > Obviously, it's been a while since 460. > > :-) > > > Ryan > > > ____________________ > BYU Unix Users Group > http://uug.byu.edu/ > ___________________________________________________________________ > List Info: http://uug.byu.edu/cgi-bin/mailman/listinfo/uug-list > ____________________ BYU Unix Users Group http://uug.byu.edu/ ___________________________________________________________________ List Info: http://uug.byu.edu/cgi-bin/mailman/listinfo/uug-list
