| soccer4net 2003-06-21, 12:41 pm |
| A veteran of networking recently challenged my understanding of ARP recently, which led me to do a little research on the subject.
I've always read (most books usually gloss over this somewhat) in the routing process, a station wants to transmit to another on a another segment, it uses ARP to find the routers MAC then the Router strips off the DL layer address, puts the MAC of the next router(over the serial link) and forwards it on. This is not how it happens.
Most encapsulation type(eg HDLC) use the same physical address everytime when referring to the the node at the other end of a P2P serial link. True ARP only runs over ethernet(as far as I know, although there are variations such as SLARP, inverse ARP which are distinctly different).
What's somewhat amazing is most textbooks have the erroneous first description above. Even Todd Lammle's CCNA 640-607 book has this error. While talking about the routing process, he has you ping between routers strictly over serial links. His reason for the first ICMP packet timing out is the router is performing IP to ethernet address mapping/ARP(funny he actually uses the term ethernet address when were using a serial link) As Anchor was saying the other day don't be afraid to challenge what you read(even in a well respected textbook)
L8er |