P2P /30 Mask over /28 between these 4 routers

Ibrahim Jamil · ‎04-01-2016

Hi Folks

why the /28 address isn't recommended between these 4 routers , why only p2p /30 is recommended between these 4 routers , pls mention pros and cons other that IP Wast

Topology attached

thanks

acampbell · ‎04-01-2016

Hi,

Look at the diagram.

Each router has 2 interfaces.

You configure seperate subnets on each link, so each end of the link requires to
be in the same subnet. Something like:-

R1 -- R2   192.168.255.254 & 253 /30
R2 -- R3   192.168.255.250 & 249 /30
R3 -- R4   192.168.255.246 & 245 /30
R4 -- R1   192.168.255.252 & 251 /30

Each of these links would need a seperate subnet.
Normally as these are like point to point we use a /30 subnet

If all 4 routers had only 1 interface to a switch then you could use the /48
for your subnet

R1 R2 R3 R4
| | | |
---------------------------- (Switch VLAN for example)

Hope this helps
Regars
Alex

Regards, Alex. Please rate useful posts.

Ibrahim Jamil · ‎04-01-2016

Hi

when using /28 between these routers , what is the pros/ functionality over /30 between these routers

what is the functionality in term of routing using /28 over /30

thanks

acampbell · ‎04-01-2016

Hi,

As I have tried to show on point to point links
we need only one ip address at each end.
Here we deploy a /30 subnet which assigns 4 addresses.

Lets say we assign 192.168.255.0/30
1- 192.168.255.0 is our actual subnet address, we cant asign this to any device.
2- 192.168.255.1 we use this at one end of the link.
3- 192.168.255.2 we use this at other end of the link.
4- 192.168.255.3 is our actual subnet broadcast address, we cant asign this to any device.

So we need a subnet that allows 2 device a /30 fits

If we had asigned a /28 subnet we would again hve a subnet & broadcast address
and would have 6 usuable addresses, we only need 2 so we waste 4.

Have a look at this URL for more info:-
http://www.cisco.com/c/en/us/support/docs/ip/routing-information-protocol-rip/13788-3.html

And use google to look for CCNA training material

Hope this helps
Regards
Alex

Regards, Alex. Please rate useful posts.

Ibrahim Jamil · ‎04-01-2016

Hi Mate

you gave me 2 answers without answering my Question :)

anyway thanks for ur time bro :)