1. The question is ambiguous. If it is asking what is the Token Frame
size, the answer is 3-bytes. (Starting Delimiter, 1-byte, Access Control,
1-byte, and End Delimeter, 1-byte). You are right in your answer, the Frame
size in TR is variable, I would have answered it the same way.
2. The average MTU for Token is 4,464, however, the data portion can
contain up to 17,800 bytes, for a MAXIMUM MTU (sorry for the redundant
redundancy) is 17,997. Cisco supports MTUs of 68-17,997 bytes. The MTU for
FDDI is 4,500.
3. Routing decision:
1) Most specific route
2) Administrative Distance
For instance, you might have a Routing table that says:
Gateway of last resort not set
R 39.0.0.0/8 [120/1] via 172.16.1.20, FastEthernet0/0
R 39.0.1.0/24 [120/1] via 172.16.1.19, FastEthernet0/0
C 172.16.0.0 is directly connected, FastEthernet0/0
If you send a packet to 39.0.1.33, it is going to use 172.16.1.19, and not
172.16.1.20 because it is the most specific route. If the route through
172.16.1.19 was not in there, and there was both an EIGRP learned route, and
the RIP route shown to 39.0.1.0, the EIGRP route would be used. Why?
Because its route has a lower Administrative Distance.
Remember, the router only places multiple equal-cost routes in the table, or
the single route with the lowest Administrative Distance. Metrics are only
used in path selection within a specific routing process, not for final
path selection. That is why we all had to learn iBgp = 200, RIP=120,
OSPF=110, IGRP=100, EIGRP=90, eBgp=20, etc. Each routing process will
present its BEST route (based on the metrics available to it) for final path
selection. That final path is chosen from the type of route it is.
K
-----
Kristopher B. Climie, CCNP, CCDP
"John Barnes" <[EMAIL PROTECTED]> wrote in message
[EMAIL PROTECTED]">news:[EMAIL PROTECTED]...
> I had technical with a CCIE interview yesterday, and
> I'm not really sure were to go with this.
>
> He asked me a lot of pretty high level questions and
> some not so high level, the problem is, I feel some of
> the answers he wanted were wrong. I'm going to post
> the questions, the answers I gave, and the answers he
> claimed to be correct. If I'm wrong on these, I'd
> like to know. If I'm right, how would you deal with
> this kind of thing?
>
> 1) What is the size of a token ring frame?
> My answer: Token ring has a variable frame size.
> His answer: 3 bytes..
>
> Isn't that the size of the Token frame?
>
> 2) What the MTU of a token ring frame? (Isn't this
> about the same question as #1?)
> My answer: slightly larger that 16K (I couldn't
> remember the exact number)
> His answer: about 4470 bytes .
>
> Ahh... what? He claimed I was thinking about
> FDDI.grrrr Ah. Who's thinking about what?
>
> 3) What is the decision making process involved when a
> packet enters a router? What three criteria are used
> to make this decision?
> My answer: It depends. Is this the first
> packet with this destination to arrive at this router?
> What switching mode is the router configured for.
>
> His answer: Forget about that stuff. how does
> it determine which route to use.
>
> My answer: longest match in the routing table
>
> His answer: What if multiple routes exist in
> the table.
>
> My answer: It depends.
>
> Ok...I'm gonna cut to the chase. The answer he
> wanted was longest match, Administrative distance,
> then metric. Ahh.. I'm pretty sure is wrong. The
> router looks at AD and Metrics long before the packet
> enters the router. The router uses AD and metric to
> populate the routing table, and then longest match
> from the routing table to make the decision once the
> packet actually enters the router. Comparing AD and
> metric on every known route every time would place
> unnecessary burden on the CPU. Compare it once, make
> the decision, and enter it in the RIT. Even in the
> case of IGRP/EIGRP with variance, the next eligible
> route is determined before the packet enters the
> router.
>
> Maybe I should have picked up on this stuff when
> the recruiter asked me with BGP was a DV or LS based
> routing protocol. My answer. ahh.neither, it's path
> vector.
>
> I'm basically sending this out to get thoughts, and
> hopefully Howard, Priscilla or someone can tell me
> wether I'm off technically or not.
>
>
> THANKS!!!!!
>
> -john
>
>
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