Chuck shaped electrons, photons, and little dot things to say:
>interesting question. without tearing up my pod to set up a Q&D, let me try
>a little logic here.
>
>when the router checks its FIB, and determines that the packet in question
>is to go out a particular interface ( as opposed to a network ) what happens
>then? does the router place that packet onto the wire out that interface, or
>does it place the packet into the process that manages what happens on that
>interface?
In the unnamed router designs which which I have the most experience,
most processing takes place on the input side, which hands the packet
off to the switching fabric ("fast path"). There's usually an
internal header indicating the destination as an interface or as a
multicast group.
Lower-layer encapsulation, output shaping, etc., do take place at the
output interface. Typically, IP fragmentation is handled there
UNLESS that has to be done in the "slow path", which normally is in
the main processor.
>
>In other words, if the packet is destined out an Ethernet interface, how is
>it handled? differently than it would be handled under other circumstances?
>I don't think so. I would think that the process that controls the Ethernet
>interface would then follow the standard operating procedure for all packets
>bound out onto an Ethernet - that there would be an ARP request. If there
>were no response from some device that knew the destination network, then
>the packet would be dropped. if there were a device, the router would then
>forward the packet.
The output interface pretty well has to be a part of ARPs, but it may
be fairly stupid with respect to them -- the ARP requests may
originate in some other processor and the ARP cache may be kept
there, depending on the design.
>
>I guess what I am saying is that the router operates in a standard manner.
>all packets that the router handles are treated the same way. meaning they
>are all processed by the appropriate router process. the router code is like
>any other computer code - a series of if-then-else sequences. all packets
>are processed the same way - inbound and outbound.
I think you are overestimating the role of interface intelligence and
underestimating how much goes on in one or more separate processors.
Of courxe, this is for high-performance routers. With 1600s and the
like, even more intelligence moves from the interface into the main
processor.
>
>in the case we have been discussing, the question I now have is whether or
>not the cable modem is responding to the ARP requests of the 1605 router.
>
>anyone have a different understanding of how the router operates?
>
>Chuck
>
>
>
>""Michael L. Williams"" wrote in message
>[EMAIL PROTECTED]">news:[EMAIL PROTECTED]...
>> "Paul Lalonde" wrote in message
>> [EMAIL PROTECTED]">news:[EMAIL PROTECTED]...
>> > but
>> > routing out via an Ethernet interface will likely just *drop* the
packet
>> > onto that broadcast domain (subnet) without pointing it to a specific
>next
>> > hop.
>>
>> This raises an interesting question: If you try to make a static route
>that
>> routes out an ethernet interface (multi-access medium), does the router
>send
>> the frame to the Layer 2 broadcast address? If so, then if there is
>another
>> router somewhere on that segment, wouldn't it hear and route the packet
>> properly, or would it see it as a layer 2 broadcast and it not go any
>> further?
>>
>> Mike W.
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