quick subnetting/acl query (CCNA) 1

[cyberspace]

I have a lab to do (see link for image)

Now the instructor said use a 255.255.240.0 mask (truth be told though, he always gets muddled up so i dont take his word as gospel)

Pic - sorry about quality

As can be seen, there are 4 subnets needed, two of which are simply point to point links, the other 2 have 2 hosts.

I was thinking that a mask of 255.255.255.224 (/27) would be more suitable for this? This would give 8 subnets/32 hosts per subnet (-2) of course.

Am I right here or does the class B mask fit the bill more? With that you get 16 subnets/4096 hosts (-2) per subnet which seems pointless for this scenario!

also a quick extended ACL question....

say for argument sake the hosts connected to the London (lower left) subnet are 186.152.1.66 and .67 respectively.

To achive the goals of the extended acl...is this correct:

access-list 101 deny tcp host 186.152.64.3 any eq 80 (denies this host all http access)
access-list 101 deny tcp any any eq 21 (denies all pcs ftp)
access-list 101 permit tcp any any eq icmp (allows all hosts to ping)

Thanks for the advice

'When all else fails.......read the manual'

 

[KiscoKid]

This appears to be an exercise in VLSM to me. So you must have a bigger subnet (supernet?) that you need to further subnet to minimize waste. The only subnet mentioned on that diagram is the /16 subnet.

I would therefore use this subnet and further subnet it. For instance the p2p links need either a /30 or /31 subnet (does the CCNA now allow you to use /31's? - I'm not sure).

The diagram isn't very clear but there seems to be just 3 nodes off each router LAN port (2 PC's and a switch). So I guess you'll need 2x/29's or perhaps 2x/28's depending on future expansion.

Regarding the ACL, it looks alright apart from the rule to permit all ICMP. That should read:

access-list 101 permit icmp any any

 

[cyberspace]

Thanks for that!

yes I agree VLSM is appropriate however its not a VLSM exercise and is just the usual "one subnet mask for all" type exercise.

You are right, you cant use /31s for CCNA no

Thanks for the ACL tip - i noticed that last night.

When it says 16 i thought that was just the classful mask for a class B address (ie 255.255.0.0) and wasnt subnetting?

'When all else fails.......read the manual'