Tylogix.com -> Cisco What Were They Thinking (WWTT) !???! Notes - The lighter side of learning Cisco.....
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The purpose
of this page is just as much to inform as it is to ask the simple question:
"What were they thinking?????" - This is a polite WTF, btw.
In
this page, I have chosen to enter oddities that I have noticed in the CCNA (so
far!) curriculum. If you have the answer, the inclination and the time, do
e-mail me if you understand the answer better than I do!
I
understand IOS is the standard, as far as routing operating systems, but truly,
some of those commands and replies make me wonder how this has come to be.
Cisco-Speak!
|
Category |
IOS "Feature" |
Explanation |
My question |
Explanations Anyone? |
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|
PPP |
ppp: ipcp_reqci: returning CONFACK |
What the Cisco router is really trying to tell you: The router has agreed on IP parameters |
What were they thinking? Does Cisco have a strange sense of humour? |
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PPP |
LCP: I CONFREQ [ACKrcvd] id 8 len 14 |
What the Cisco router is really trying to tell you: One router has suggested PAP
authentication, the other has accepted
authentication, but suggested CHAP authentication |
Wow, that was real obvious! |
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|
erase startup-config delete
vlan.dat |
What the Cisco router is really trying to tell you: - the
verb "erase" is applicable to memory - the verb "delete" is applicable
to a file |
Why not use one verb only, like "clear"? Too
simple? |
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Command Mode |
Access Method |
Prompt |
Fact: - In
the Exec mode, the verb show is allowed. - In
the Global Configuration mode, verbs such as show and ping are NOT allowed. To overcome the fact that the show command is not allowed, Cisco introduced an override verb, which does allow the show and ping to work in Global Configuration mode - as in : "do show" or "do ping" |
Why not simply allow the show and ping command
in Global Configuration mode? Why use <my opinion> the most cheesy "do show" or "do
ping" instead? To boot, "do ?" in Global Configuration mode does not yield the possible
commands it allows to perform.... What was the idea? |
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EXEC |
Log in. |
Router> |
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|
EXEC |
From user EXEC mode, issue the enable command. |
Router# |
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Global Configuration |
From privileged EXEC mode, issue the configure terminal
command. |
Router(config)# |
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line
console 0 logging
synchronous |
Without these two instructions, anything you type may be
interrupted by spurts of Cisco messages. |
Why is logging not synchronous by default? |
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Frame
Relay |
Router#show frame-relay map Serial0/0/0
(up): ip 175.15.3.22 dlci
201(0xC9,0x3090), dynamic, broadcast, status defined, active |
What the Cisco router is really trying to tell you: Serial 0/0/0 has the feature frame-relay
inverse-arp enabled. |
How obvious is that? |
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Elections |
- OSPF likes to use the highest
RID or IP address as the Designated
Router (DR) - Switches like to use the lowest
Mac Address to elect the Root Bridge |
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One high, one low.... Why so many inconsistent methods? |
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EIGRP |
In EIGRP,
Cisco's prized protocol, a "Successor" is a neighbouring router
used for packet forwarding that has the least cost path to a destination that
is guaranteed not to be part of a routing loop. In
effect, confusingly the designation "Successor" is a first choice
route, and "Feasible Successor" as a backup to the "Successor.
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Why use such confusing terminology? Successor to what? Why not use "primary route" and "backup route"? |
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Memory |
- Flash: Stores IOS - NVRAM: Non-Volatile RAM, stores
router configuration, aka startup-config - RAM:Random
Access Memory |
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IOS memory? I guess "flash" looked more
"flashy".... Configuration memory? NVRAM, well, I guess you have to figure
out for yourself what it contains. |
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Can anyone explain how the protocol abbreviations
were decided upon?
|
Routing Abbreviation |
Routing Protocol |
|
B |
BGP |
|
* |
Candidate default |
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C |
Connected |
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E |
EGP |
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D |
EIGRP |
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EX |
EIGRP External |
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I |
IGRP |
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i |
IS-IS |
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L1 |
IS-IS - Level 1 |
|
L2 |
IS-IS - Level 2 |
|
ia |
IS-IS Inter Area |
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M |
Mobile |
|
O |
ODR |
|
E1 |
OSPF External Type 1 |
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E2 |
OSPF External Type 2 |
|
N1 |
OSPF NSSA External Type
1 |
|
N2 |
OSPF NSSA External Type
2 |
|
P |
Periodic Download
Static Route |
|
U |
Per-User Static Router |
|
R |
RIP |
|
S |
Static |
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