>At 10:35 AM 2/7/01, Howard C. Berkowitz wrote:
>>I am also confused about the question itself.
>>
>>The basic default behavior of Cisco routers is to try to identify the
>>protocol type of a frame, and send it either to the bridging code or
>>the router code for that protocol on that interface. If the
>>protocol type is not supported, drop the frame.
>>
>>I don't know this, but I can reasonably assume that IP protocol
>>identification is hard-coded for the Ethernet II IP Ethertype and for
>>802.2 IP. IP might be treated as a special case, of which the router
>>is agnostic about encapsulation Still, the encapsulation should be
>>meaningful if and only if appropriate routing or bridging is enabled
>>for the interface.
>
>That would be my assumption also. And, it is probably hard-coded to
>recognize the EtherType for ARP also.
>
>There were some cases of TCP/IP stacks using 802.3/802.2 and SNAP for IP
>and ARP. They weren't very popular. But if you had some devices using them,
>then you would have to configure the router to send ARPs that way. There is
>also something called an HP Probe that accomplishes the same thing as ARP
>in a non-standard way.
>
>So there is an interface "arp {arpa | probe | snap}" command. I doubt that
>it's used much. Encapsulation is much more of an issue for Novell.
>
>This discussion has lost its steam. We might want to end it.... &;-)
>
>Priscilla
I have long been of the opinion that certain networking problems are
insoluble without doctoral-level intervention. In at least some of
them, the specific doctor required would be named Kevorkian.
>
>
>>ARP has a protocol type field so that wouldn't seem like the reason.
>>
>>
>> >Okay, I have a guess...a total W.A.G., and I wasn't able to back it
>> >up with some quick research, but here it is:
>> >
>> >The answer to this has something to do with ARP packets. My guess
>> >is that they assume the presence of Ethernet_II frames when
>> >constructing ARP packets and these would be inoperable if some other
>> >ethernet frame were being used.
>> >
>> >That would explain why the default *had* to be Ethernet_II. If ARP
>> >breaks, IP over ethernet breaks.
>> >
>> >Am I right?? I'm going to keep digging to see if I can find some
>> >more details about this. I may be chasing down the wrong street.
>> >Let me know if I'm even close! :-)
>> >
>> >John
>> >
>> >>
>> >> OK, Leigh Anne, you're just going to have to come out and tell us
>> what you
>> >> are getting at. The suspense is killing me. &;-)
>> >>
>> >> The only time I've ever configured an Ethernet encapsulation,
>>it has been
>> >> part of the ipx network command. As we know, Novell mucked things up and
>> >> supports four frame types, so being able to configure the frame type is
>> >> necessary for IPX. A unique feature of IPX is that you can configure
>> >> multiple networks on a single segment. Each of them must have
>>a different
>> >> encapsulation. In fact that is how you support networks with devices
>> >> configured for different encapsulations.
>> >>
>> >> I don't even know that you can configure the encapsulation for IP on
>> >> Ethernet on a router. Can you? Or is that what you're getting at. IP
>> >> doesn't care.
>> >>
>> >> With IP, 99% of the world uses Ethernet V2 (dest, src,
>>EtherType). I just
>> >> tried to change it on my PC and I couldn't, although I think I have seen
>> >> that capability on other PCs. But my guess is that if I did change
>> it, the
>> >> router could still handle it.
>> >>
>> >> Priscilla
>> >>
>> >> At 12:33 PM 2/7/01, Tony van Ree wrote:
>> >> >Hi,
>> >> >
>> >> >I understood it to tell me that there is a common method used by a
>> number
>> >> >of manufacturers and protocols. Some other companies and protocols had
>> >> >made some changes. The default was used as it was the most
>> >> >common. Ethernet_II had been around for quite a while before the 802.3
>> >> >and almost all devices manufacturers ethernet cards and the like could
>> >> >handle Ethernet_II but not necessarily 802.3.
> > >> >
>> >> >Maybe I mis understood.
> > >> >
>> >> >Teunis
>> >> >
>> >> >
>> >> >On Tuesday, February 06, 2001 at 05:36:32 PM, [EMAIL PROTECTED] wrote:
>> >> >
>> >> > > I did read Priscilla's post. She addressed the issue of WHY
>> >>Ethernet_II is
>> >> > > the default frame type selected for IP, but didn't examine why IP
>> >> > requires a
>> >> > > default frame type in the first place. IPX uses a default
>>frame type
>> >> > > because different Ethernet encapsulations are not able to co-exist
>> >> > within an
>> >> > > IPX network -- however different Ethernet encapsulations
>> >>(Ethernet_II and
>> >> > > Ethernet 802.3) ARE able to co-exist within an IP network. As such,
>> >> > what is
>> >> > > the importance of a default Ethernet encapsulation for IP?
>> >> > >
>> >> > > That's what I've been challenging John to think about. Once
>> >>he understands
>> >> > > where the default Ethernet encapsulation comes into play, he
>> >>could answer
>> >> > > his question as to whether there "would there be a good reason
>> >>to change to
>> >> > > a
>> >> > > different frame type, or would we only benefit from a
>> >>different frame type
>> >> > > in a non-IP environment or mixed environment".
>> > > > >
>> >> > >
>> >> > >
>> >> > >
>> >> > > -----Original Message-----
>> >> > > From: Tony van Ree [mailto:[EMAIL PROTECTED]]
>> >> > > Sent: February 6, 2001 5:06 PM
>> >> > > To: [EMAIL PROTECTED]; John Neiberger; [EMAIL PROTECTED]
>> >> > > Subject: RE: Another 802.3 and Ethernet Question
>> >> > >
>> >> > >
>> >> > > Hi,
>> >> > >
>> >> > > I'm sorry I did not cover the rest of the ethernat frame
>> >>types. This was
>> >> > > covered earlier this week. Priscilla covered it really well
>> >>in one of her
>> >> > > replys on a similar question.
>> >> > >
>> >> > > Teunis
>> >> > >
>> >> > >
>> >> > > On Tuesday, February 06, 2001 at 04:55:01 PM,
>>[EMAIL PROTECTED] wrote:
>> >> > >
>> >> > > > Yes, with respect to IPX, that's correct--and that
>>answers my first
>> >> > > > question.
>> >> > > >
>> >> > > > My second question asked about what was the purpose of a
>> >>default Ethernet
>> >> > > > frame type for use with IP. Using IPX as an analogy, does a
>> >>router only
>> >> > > > route Ethernet_II frames if no Ethernet frame type has been
>> specified?
>> >> > > Does
>> >> > > > a router drop IEEE 802.3 frames by default? To route IEEE
>> >>802.3 frames,
>> >> > > is
>> >> > > > any additional configuration required?
>> >> > > >
>> >> > > > And with that, we're lead back to John's original question:
>> >>What is the
>> >> > > > purpose of a default Ethernet frame type for IP?
>> >> > > >
>> >> > > > -----Original Message-----
>> >> > > > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On
>> Behalf Of
>> >> > > > Tony van Ree
>> >> > > > Sent: February 6, 2001 2:51 PM
>> >> > > > To: Leigh Anne Chisholm; John Neiberger; [EMAIL PROTECTED]
>> >> > > > Cc: Priscilla Oppenheimer
>> >> > > > Subject: RE: Another 802.3 and Ethernet Question
>> >> > > >
>> >> > > >
>> >> > > > Hi,
>> >> > > >
>> >> > > > Those not specified by the router are either routed by the
>> server or
>> >> > > produce
>> >> > > > IPX protol errors and are dropped.
>> >> > > >
>> >> > > > It is important not to have the various frame types set on
>> >>the servers or
>> >> > > > service advertisers. If for example you are normally using
>> >>Novell-Ether
>> >> > > > (802.3) and you put in a server using Netware 4.x running SAP
>> (802.2).
>> >> > > Now
>> >> > > > when you put in the first server you configure both the SAP and
>> Novell
>> >> > > Ether
>> >> > > > in the server. You have 802.3 (Novell-ether) configured in
>> >>the router.
>> >> > > > Pull out the original server and you have no network. Othen
>> >>you will lose
>> >> > > > half of your local clients.
>> >> > > >
>> >> > > > Have lose networks and or frame types can also create
>>some horrible
>> >> > little
>> >> > > > routing loops and unwanted traffic. SAP's, RIP updates etc.
>> >> > > >
>> >> > > > Let the router route and servers serve.
>> >> > > >
>> >> > > > Another one that sometimes grabs you.
> > >> > > >
>> >> > > > Teunis,
> > >> > > > Hobart, Tasmania
>> >> > > > Australia
>> >> > >
>> >> > >
>> >> > >
>> >> >
>> >> >
>> >> >--
>> >> >www.tasmail.com
>> >> >
>> >> >
>> >> >_________________________________
>> >> >FAQ, list archives, and subscription info:
>> >> >http://www.groupstudy.com/list/cisco.html
>> >> >Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
>> >>
>> >>
>> >> ________________________
>> >>
>> >> Priscilla Oppenheimer
>> >> http://www.priscilla.com
>> >>
>> >> _________________________________
>> >> FAQ, list archives, and subscription info:
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>> >
>> >
>> >Find the best deals on the web at AltaVista Shopping!
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>> >
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>
>
>________________________
>
>Priscilla Oppenheimer
>http://www.priscilla.com
>
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