Settle an argument

[mightyscotchpine]

I'm trying to get some networking professionals to weigh in on this question, hence my choice of forums.

Given a host with an IP of 200.200.200.150, and a subnet mask of 255.255.255.128, is the following considered an acceptable way to write the address in CIDR notation:

200.200.200.150/25


Thanks in advance for helping out.

 

[unclerico]

yes

I hate all Uppercase... I don't want my groups to seem angry at me all the time! =)
- ColdFlame (vbscript forum)

 

[VinceWhirlwind]

Seems OK to me - what are the objections?

 

[cisconooblet]

yes.

CCNA, BCNE, Security+, Network +

 

[baddos]

CIDR = classless routing

The Internet uses classless routing now instead of the old original classfull routing of the past.

So the correct way to refer to an allocated subnet like that is to use the CIDR notation.

 

[mightyscotchpine]

VinceWhirlwind,

The objection (which I disagree with) is that the subnet bits should *only* be written out when writing the number of a network, not a host.

 

[VinceWhirlwind]

Well, I guess if somebody does a "show run interface G1/1" compared to a "sh ip route", they might decide what you've been told is true, however, if what you've been told is true, how come an IP route statement looks like this:
ip route 10.15.20.0 255.255.255.0 10.226.10.21

The bottom line is that /25 means exactly the same thing as 255.255.255.128, therefore you can use them interchangeably when you are communicating some design details.
/25 takes up less room than 255.255.255.128, so it is a better way to communicate the information, UNLESS you're dealing with low-grade IT staff to whom you want to make the subnet mask absolutely clear, in which case you use 255.255.255.128 to avoid them being confused.

 

[leedsit]

Given a host with an IP of 200.200.200.150, and a subnet mask of 255.255.255.128, is the following considered an acceptable way to write the address in CIDR notation:

200.200.200.150/25"

Perfectly normaly, anyone who knows IP well enough will understand what it means, I would personally prefer to write 200.200.200.128/25 which shows the network for that subnet rather than a host in that subnet, but thats personal preference. Either way is good.

Lee.



LEEroy
CCNP,CCIP

 

[Cluebird]

My 2 cents. A complete IP address requires both the address and the mask. Neither piece by itself gives full information about the address.

For example: Given the address 172.25.33.55, how is it subnetted? Ans. Not enough information given. Best guess is it is at classful mask /16. When I give you the mask 255.255.255.128 you have enough information to know this Class B has been subnetted with 9 bits for a total mask of /25 (255.255.255.128).

Or this: What class is the mask 255.255.255.0? Again, not enough information given. You need an address to give context. This mask can be applied to Class A, Class B, or Class C. When I give you the context 123.55.55.67, you can answer the question.

Both dotted decimal and prefix notation are valid ways to write an address. Unfortunately, IOS doesn't let you use prefix notation with IPv4 to add an address to an interface. IPv6 does and uses prefix notation exclusively.

HTH

 

[jneiberger]

Not only is it perfectly acceptable, it's how it's done on Juniper routers, just to give a little different perspective. If you entered "200.200.200.150 255.255.255.128" on a Juniper, it would have no idea what the heck you were doing. Cisco's way isn't the only way to do things.

 

[cflcrosland]

I agree with all the comments above!

 

[Almin]

so do I

 

[burtsbees]

OK, here's a wake-up call for all of you missing the COMPLETE OBVIOUS!!!!!

...nah, just kidding.

So, the way the person with whom you object would suggest to write the ip address out in proper notation so as to indicate it is a host address rather than a wire address would be to purposely leave out the mask info, whether in dotted-dec. or CIDR, unless the network number would need to be indicated? How many people in here would have retained their jobs adhering to this...method, for lack of better words? It seems to me that perhaps your advisor is in the learning stages of subnetting...as are you also, perhaps maybe possibly? Did your buddy indicate why he/she would purposely leave out info that is necessary more often than not?

OR...

is this person YOU?!?! lol

kidding...

hey, people---how goes it?

/~~~R:E:W:T~~~

10 ? "TIMMAY!!!"
20 goto 10
run
TIMMAY!!!
TIMMAY!!!
TIMMAY!!!
TIMMAY!!!
TIMMAY!!!
TIMMAY!!!
TIMMAY!!!
TIMMAY!!!
TIMMAY!!!
TIMMAY!!!
TIMMAY!!!
TIMMAY!!!
TIMMAY!!!
TIMMAY!!!
TIMMAY!!!
TIMMAY!!!
TIMMAY!!!
TIMMAY!!!
TIMMAY!!!
TIMMAY!!!
TIMMAY!!!
TIMMAY!!!
TIMMAY!!!
TIMMAY!!!
TIMMAY!!!
TIMMAY!!!
TIMMAY!!!
TIMMAY!!!
TIMMAY!

 

[unclerico]

hey, people---how goes it?

Whoa!!!! Who dis is?? The man back from retirement?? Did you sit your CCIE Security lab yet??

I hate all Uppercase... I don't want my groups to seem angry at me all the time! =)
- ColdFlame (vbscript forum)