From: Andy mrozek (andymrozek@yahoo.com)
Date: Sun Jul 18 2004 - 02:57:44 GMT-3
CDP as far as I know is a layer 2 protocol , so you
can have CDP showing up and still have an encap
failure , from your layer 3 to layer 2 protocol. Did
you try a debug ip packet ?? Curious if that would
have given any insight as to the cause of the
problem.... So even if you don't have a layer 3
protocol defined on your interface as long as there is
a global "cdp run" and interface level "cdp enable"
you will see other cisco devices....
--- "Terrence Rouse (trouse)" <trouse@cisco.com>
wrote:
> Thanks Brian,
>
> That makes sense. I know what an "ENCAP FAILURE" is
> and I know all about
> ARP. Well I thought I did :-). But I didn't check
> the ARP cache. I
> thought I would have to get pass the encap failure
> before it would even
> initiate and ARP request. IF it cant identify the
> interface how will it
> know where to send the ARP out. And the CDP threw
> me off too.
>
> Thanks for all the help.
>
> T
>
> -----Original Message-----
> From: Brian McGahan
> [mailto:bmcgahan@internetworkexpert.com]
> Sent: Saturday, July 17, 2004 10:43 PM
> To: trouse@cisco.com; ccielab@groupstudy.com
> Subject: RE: ENCAP FAILURES ON ETHERNET
>
>
> "I am still not sure how I fixed it but I had some
> stuff messed up on the
> 3550 with my VLAN setup."
>
> That is how you fixed it. Like Ken mentioned,
> encapsulation failure
> means that the router doesn't know what layer 2
> address to put in the
> packet. If the next hop device was not within your
> broadcast domain (i.e.
> wrong VLAN assignment) it would not have received
> your Ethernet ARP packet.
> Furthermore it would not have been able to reply
> with its MAC address, so
> the router initiating the ping packet wouldn't know
> what address to put in
> the frame, hence encapsulation failure.
>
>
> HTH,
>
> Brian McGahan, CCIE #8593
> bmcgahan@internetworkexpert.com
>
> Internetwork Expert, Inc.
> http://www.InternetworkExpert.com
> Toll Free: 877-224-8987 x 705
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>
>
> > -----Original Message-----
> > From: nobody@groupstudy.com
> [mailto:nobody@groupstudy.com] On Behalf
> Of
> > trouse@cisco.com
> > Sent: Saturday, July 17, 2004 8:34 PM
> > To: ccielab@groupstudy.com
> > Subject: ENCAP FAILURES ON ETHERNET
> >
> > I saw something today the blew my mind and time.
> Guess I always take
> > ethernet for granted. But today i was getting
> encapsulation failure
> on
> > fastethernet. I had a ip addresss configure but
> it seems as if the
> didnt
> > recognize it as connected, however it showed up
> connected in ip route.
> > The "sh int fa 0/0" was up/up. CDP was showing
> neighbor but I could
> not
> > pass ip traffic. I am still not sure how I fixed
> it but I had some
> stuff
> > messed up on the 3550 with my VLAN setup. And
> after sorting all this
> out.
> > Pings worked and encap failure went away. It was
> doing it on all my
> > routers so I want to say it was the switch but....
> >
> >
> > my question is: is there anyway the cat can cause
> the routers port to
> > encap fail. I check the duplex/speed setting and
> all loooked find on
> both
> > ends but it was auto negotiated. If this had been
> my real lab I think
> I
> > would have cried. Spend over an hour before it
> finally started
> working
> > and this was a timed MOCK lab from NM (CheckIt).
> so I was pretty
> > disappointed and upset that my time was wasted.
> Could this had been a
> > bug?
> >
> > Of couuse the interface was "no shut" since I was
> getting CDP over it
> and
> > it saw the connected cat3550 switch.
> >
> > Thanks
> > PUZZLED.....
> >
> >
>
This archive was generated by hypermail 2.1.4 : Sun Aug 01 2004 - 10:11:58 GMT-3