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Re: [SPAM]Re: I know this CCIE who wouldn't know a packet if it hit him in the ass! ~CCIE Interview Qs~ posted 12/06/2007
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I suppose so.

That's a very good link by Joe.

I must read it sometime :)

Gary
----- Original Message ----- From: "Scott Vermillion" <scott_ccie_list@xxxxxxxxx>
To: "'Gary Duncanson'" <gary.duncanson@xxxxxxxxxxxxxx>
Cc: <ccielab@xxxxxxxxxxxxxx>
Sent: Thursday, December 06, 2007 10:06 PM
Subject: RE: [SPAM]Re: I know this CCIE who wouldn't know a packet if it hit him in the ass! ~CCIE Interview Qs~



Good question Gary. My suspicion is that yes, the default route is at the
very bottom of the FIB. I did a quick read of Odom's Cert Guide (3rd
Edition) and he didn't really touch on default routes from a CEF
perspective. However, I was reminded that the FIB is organized into a
construct called an "mtrie." If I understand things correctly, this is
organized such that you get a more specific match towards the top and a less
specific match towards the bottom (this reduces average lookup time). So
presumably 0.0.0.0, if present in the RIB, would be found at the very bottom
of the FIB. I would guess that there would be a L2 header cached for the
0.0.0.0 next hop in the adjacency table.


Notice my use of the words "suspicion," "presumably," and "guess" here...


-----Original Message-----
From: Gary Duncanson [mailto:gary.duncanson@xxxxxxxxxxxxxx]
Sent: Thursday, December 06, 2007 2:52 PM
To: Scott Vermillion
Cc: ccielab@xxxxxxxxxxxxxx
Subject: Re: [SPAM]Re: I know this CCIE who wouldn't know a packet if it hit
him in the ass! ~CCIE Interview Qs~


What happens when a L3 switch receives a frame destined for a L3 destination

that is unknown to the router which has to recourse to a default route? Do
default route interfaces and outbound L2 headers get translated into FIB?

I think Odom covers some of this.

Gary
----- Original Message ----- From: "Scott Vermillion" <scott_ccie_list@xxxxxxxxx>
To: "'Jian Gu'" <guxiaojian@xxxxxxxxx>; "'Gary Duncanson'"
<gary.duncanson@xxxxxxxxxxxxxx>
Cc: "'Darren Johnson'" <dazza_johnson@xxxxxxxxxxx>; <ccielab@xxxxxxxxxxxxxx>
Sent: Thursday, December 06, 2007 9:41 PM
Subject: RE: [SPAM]Re: I know this CCIE who wouldn't know a packet if it hit


him in the ass! ~CCIE Interview Qs~


Hey all,

Certainly it's great to know what the process would be sans CEF/MLS, but
in
modern switching architectures, we aren't actually doing these lookups
based
on flows or packet/frame arrival, right?  My studies of CEF for the
written
caused me to look a little more deeply into this than I ever had
previously.
What I recall (and what Joe's article seems to confirm) is that
information
populated into the RIB gets translated into a FIB by CEF.  Then the
adjacency table actually caches the full L2 header for each and every
entry
in the FIB.

So before the first flow ever takes place, we've already pre-calculated
not
only the outgoing interface for every L3 destination, we've also cached
the
outbound L2 header.  This all gets pushed down to ASICs that essentially
match on bit patterns.  In other words, both L2 and L3 are switched down
in
hardware and all of this is set up at system boot time.  Then the RP
simply
pushes changes in the RIB over to CEF, which maintains the FIB.

Now where I get a bit fuzzy is how QoS policy and that sort of thing gets
inserted into the mix.  I'm not a chip designer and I don't aspire to be.
I'm willing to take some things on faith, and this is probably one such
thing.

And I understand you too Darren!  A host or another router viewing the
local
box in question as the next hop would perform L2 encapsulation with the
destination MAC set to that of this local box.  But I still think that,
due
to CEF, in such a case we're still just dealing with a L3 switching
operation vs. a L2 switching operation.

Right?

Scott


-----Original Message----- From: nobody@xxxxxxxxxxxxxx [mailto:nobody@xxxxxxxxxxxxxx] On Behalf Of Jian Gu Sent: Thursday, December 06, 2007 2:12 PM To: Gary Duncanson Cc: Darren Johnson; ccielab@xxxxxxxxxxxxxx Subject: Re: [SPAM]Re: I know this CCIE who wouldn't know a packet if it hit him in the ass! ~CCIE Interview Qs~

Assuming MACs are leaned and ARPs are all resolved.

When a frame comes in, router/switch will do both L2 and L3 lookup at the
same time, and combine the result to make the final decision. If
destination
MAC is router, then L2 lookup will not yield something meaningful, L3
lookup will come out with MAC re-write information for nexthop for
destination IP, frame will then be routed. If destination MAC is not
router,
this MAC must be in the vlan's dynamic MAC table, in this case, L2 lookup
will yield outgoing port, L3 lookup better come with the same result, this
frame will be L2 switched.


Jian

On Dec 6, 2007 12:40 PM, Gary Duncanson <gary.duncanson@xxxxxxxxxxxxxx>
wrote:

Daz,

Yeah. Well it's getting later here in GB.

Packet comes in..

If the destination MAC address is that of the L3 switch, then it knows
about
it, doesn't it just switch it out the right interface?

If unknown..what about ARP or routing?

Im sure you know what you mean :-)

Gaz
----- Original Message -----
From: "Darren Johnson" <dazza_johnson@xxxxxxxxxxx>
To: "'Gary Duncanson'" <gary.duncanson@xxxxxxxxxxxxxx>
Cc: <ccielab@xxxxxxxxxxxxxx>
Sent: Thursday, December 06, 2007 8:33 PM
Subject: RE: [SPAM]Re: I know this CCIE who wouldn't know a packet if it
hit
him in the ass! ~CCIE Interview Qs~


> Hey Gaz, starting to like our late night chats ;-)
>
> My point was that if the destination MAC address is that of the L3
switch,
> it is to be routed. If it isn't and the receiving interface is L2 then
it
> is
> switched/bridged.
>
> Hmmm, not sure if Im making myself clear. I know what I mean...... :-)
>
> Daz
>
> -----Original Message-----
> From: Gary Duncanson [mailto:gary.duncanson@xxxxxxxxxxxxxx]
> Sent: 06 December 2007 19:50
> To: Darren Johnson
> Cc: ccielab@xxxxxxxxxxxxxx
> Subject: [SPAM]Re: I know this CCIE who wouldn't know a packet if it
> hit
> him
> in the ass! ~CCIE Interview Qs~
>
> Would that not be destination MAC known by the L3 switch (switched) as
> opposed to unknown (routed)?
>
> Is it not switched instead of bridged ;) What about those damn ASICs?
> I
> have chatted offline with a guru who suspects CEF is the route of the
evil
> these days (no pun intended) as opposed to the MLS-SE, MLS-RP, MLSP
stuff
> and he may comment soon.
>
> You know who you are ;)
> ----- Original Message -----
> From: "Darren Johnson" <dazza_johnson@xxxxxxxxxxx>
> To: "'Gary Duncanson'" <gary.duncanson@xxxxxxxxxxxxxx>; "'Jian Gu'"
> <guxiaojian@xxxxxxxxx>
> Cc: <ccielab@xxxxxxxxxxxxxx>
> Sent: Thursday, December 06, 2007 7:28 PM
> Subject: RE: I know this CCIE who wouldn't know a packet if it hit him
in
> the ass! ~CCIE Interview Qs~
>
>
>> IMHO, if the destination MAC is owned by the L3 switch, then it needs
to
>> be
>> routed. If the destination MAC is not owned by the L3 switch, it can
>> either
>> bridge it (if the device is located on another interface) or drop it
(if
>> the
>> device is located on the same interface the frame was received on).
>>
>> Dazzler
>>
>> -----Original Message-----
>> From: nobody@xxxxxxxxxxxxxx [mailto:nobody@xxxxxxxxxxxxxx] On Behalf
>> Of
>> Gary
>> Duncanson
>> Sent: 06 December 2007 17:51
>> To: Jian Gu
>> Cc: ccielab@xxxxxxxxxxxxxx
>> Subject: Re: I know this CCIE who wouldn't know a packet if it hit >> him
in
>> the ass! ~CCIE Interview Qs~
>>
>> Sounds like the route once switch many thing to me from MLS studies..
>>
>> Gary
>> ----- Original Message -----
>> From: "Jian Gu" <guxiaojian@xxxxxxxxx>
>> To: "Sohail Nedaria" <sohail.nedaria@xxxxxxxxx>
>> Cc: "ccie ccie" <cciefun@xxxxxxxxx>; "Narbik Kocharians"
>> <narbikk@xxxxxxxxx>; "Cisco certification" <ccielab@xxxxxxxxxxxxxx>
>> Sent: Thursday, December 06, 2007 6:54 AM
>> Subject: Re: I know this CCIE who wouldn't know a packet if it hit >> him
in
>> the ass! ~CCIE Interview Qs~
>>
>>
>>> Sure, here is one I like,
>>>
>>> How does a L3 switch router know when to L2 switch an incoming frame
and
>>> when to L3 switch an incoming frame?
>>>
>>> On Dec 5, 2007 10:00 PM, Sohail Nedaria <sohail.nedaria@xxxxxxxxx>
>>> wrote:
>>>
>>>> Hi Guys
>>>>
>>>> Can you guys provide me CCIE Interview questions so i
can
>>>> also prepare my self well before i take on any interview.
>>>>
>>>> Thanks
>>>> Suhail
>>>> CCIE#19337
>>>>
>>>>
>>>> On 12/6/07, ccie ccie <cciefun@xxxxxxxxx> wrote:
>>>> >
>>>> > Hi,
>>>> >
>>>> > I am going off bit, but like to share something with you.
>>>> >
>>>> > I gave lots of interview include CISCO, Google, Yahoo......no end
>>>> > &
i
>>>> gave
>>>> > with out any interest to join but to test myself :). I gave
>>>> > interview
>>>> for
>>>> > small to big organization & i found you can't impress the
interviewer
>>>> only
>>>> > by your techniqual knowledge.
>>>> >
>>>> > Thing to impress them as per my understanding are as.
>>>> >
>>>> > 1. Good Techniqual Approach
>>>> > 2. If you dont know say you dont know this time, but you will
>>>> > learn
&
>>>> find
>>>> > the answer.
>>>> > 3. Good troubleshooting approach (In network always answer withh
>>>> refrance
>>>> > to
>>>> > OSI layer)
>>>> > 4. Listen interviewer carefully take own time to think & answer
>>>> > 5. Never underestimate interviewer who knows what the other side
>>>> > person
>>>> > is.
>>>> > 6. Respect interviwer & appreciate him for some good question.
>>>> > 7. Before go to the interview do your study about the >>>> > oganization.
>>>> > 8. Last be not least. Give an impression that you respect the
>>>> organization
>>>> > lot, you will love to work for them, you will give longer
association
>>>> > &
>>>> > your
>>>> > placement in organization will contributing lot to generate
revenue.
>>>> >
>>>> > Dont forget final interview is always by the management people.
>>>> >
>>>> >
>>>> > Regards,
>>>> > Mike
>>>> >
>>>> >
>>>> >
>>>> > On 12/6/07, Narbik Kocharians <narbikk@xxxxxxxxx> wrote:
>>>> > >
>>>> > > Darth, Are you a CCIE? I don't see your number. But what would
you
>>>> hate
>>>> > to
>>>> > > be asked in the interview? that's the question i would ask.
>>>> > > I would ask him/her what are your weak points and what are your
>>>> > > strong
>>>> > > points. Go from there.
>>>> > > Talk to him/her about some of the problems that your firm had
>>>> > > and
>>>> > > see
>>>> > > what the person responds, but don't expect the poor CCIE to
>>>> > > solve
>>>> > > it
>>>> for
>>>> > > you
>>>> > > in a second. But he/she should have an idea as to where to >>>> > > look,
>>>> > > from
>>>> > that
>>>> > > you should know the depth of his/her knowledge.
>>>> > > If you or the interviewer is experienced enough, the second >>>> > > this
>>>> person
>>>> > > opens his/her mouth, you should know the depth of his >>>> > > knowledge.
>>>> > >
>>>> > > But once again, CCIEs are not gods, they can have a bad day as
>>>> > > well.
>>>> > > I
>>>> > > personally like to focus on the person's attitude and
personality,
>>>> > > obviously
>>>> > > he/she got the CCIE cert, which means that the person either
knows
>>>> > > or
>>>> > knew
>>>> > > the stuff and can easily pick up the info.
>>>> > >
>>>> > >
>>>> > > My 2 Cent.
>>>> > >
>>>> > > On 12/5/07, darth router <darklordrouter@xxxxxxxxx> wrote:
>>>> > > >
>>>> > > > Ok guys,
>>>> > > >
>>>> > > > there was a thread a while back talking about dumbass CCIE's.
As
>>>> > > > I
>>>> > > prefer
>>>> > > > not to be the dumbest CCIE on the planet, help me out with
>>>> > > > questions
>>>> > > that
>>>> > > > you might ask a CCIE candidate in an interview. I have had
>>>> > > > some
>>>> brutal
>>>> > > > interviews since I became IE. Honestly the questions seem a
>>>> > > > bit
>>>> basic
>>>> > so
>>>> > > > far, but I have had some really in depth questions about
>>>> > spanning-tree,
>>>> > > > troubleshootin real world EIGRP scenarios, etc.. that really
>>>> > > > caught
>>>> me
>>>> > > off
>>>> > > > guard. It's not that I could not have solved these issues, >>>> > > > had
I
>>>> been
>>>> > > > there
>>>> > > > logged into the routers, its explaining things we take for
>>>> > > > granted
>>>> can
>>>> > > be
>>>> > > > tough, especially in interviews. It seems like a lot of
>>>> > > > people are amazed that a CCIE couldn't answer this or that
>>>> > > > question.
>>>> > > > Personally, I am trying to come up with a knowledge
>>>> > > > maintanance
>>>> plan,
>>>> > > > like reading a chapter in the exam cert guide every week. The
>>>> > > > tasks
>>>> I
>>>> > > > do not do on a daily basis fade quickly.
>>>> > > >
>>>> > > >
>>>> > > > I have of late been going way back to basics, reading up on
>>>> > > > TCP/IP
>>>> > > flows,
>>>> > > > Ethernet, ARP, looking at packet sniffing traces, etc..
>>>> > > > Someone
>>>> > > > made
>>>> > > > mention
>>>> > > > of the CAM table populating entries, so I read up on that >>>> > > > too.
>>>> > > >
>>>> > > > I certainly don't know everything, but I would love to. Care
>>>> > > > to
>>>> > > > give
>>>> > me
>>>> > > > some
>>>> > > > example questions you might ask a CCIE in an interview, or
>>>> > technologies
>>>> > > > you
>>>> > > > would expect to have him/her to have down pat?
>>>> > > >
>>>> > > > DR
>>>> > > >
>>>> > > >
>>>> >
> _______________________________________________________________________
>>>> > > > Subscription information may be found at:
>>>> > > > http://www.groupstudy.com/list/CCIELab.html
>>>> > > >
>>>> > >
>>>> > >
>>>> > >
>>>> > > --
>>>> > > Narbik Kocharians
>>>> > > CCIE# 12410 (R&S, SP, Security)
>>>> > > CCSI# 30832
>>>> > > www.MicronicsTraining.com
>>>> > > Sr. Technical Instructor
>>>> > > www.Net-WorkBooks.com
>>>> > >
>>>> > >
>>>>
_______________________________________________________________________
>>>> > > Subscription information may be found at:
>>>> > > http://www.groupstudy.com/list/CCIELab.html
>>>> >
>>>> >
> _______________________________________________________________________
>>>> > Subscription information may be found at:
>>>> > http://www.groupstudy.com/list/CCIELab.html
>>>> >
>>>>
>>>>
>>>>
>>>> --
>>>> Thanks And Regards
>>>> Suhail.U.Nedaria
>>>> 9833256425
>>>> CCIE# 19337.
>>>>
>>>>
_______________________________________________________________________
>>>> Subscription information may be found at:
>>>> http://www.groupstudy.com/list/CCIELab.html
>>>
>>>
_______________________________________________________________________
>>> Subscription information may be found at:
>>> http://www.groupstudy.com/list/CCIELab.html
>>
>>
_______________________________________________________________________
>> Subscription information may be found at:
>> http://www.groupstudy.com/list/CCIELab.html
>>
>>
>>
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