VLSM Routing

MaxRobinson · January 2023

Hi,
I'm attempting to configure my first network using subnets but I'm struggling to setup the IPs for a link between two routers.
When I was designing my addressing, I assigned 192.168.4.131 /30 to one port and 192.168.4.132 /30 for the other, however when I try to assign this on the router with 'ip address 192.168.4.131 255.255.255.252' it tells me it is a bad mask yet I've seen others use similar IPs.
So my question would be can anyone point me towards the issue with this ip and mask for this serial link?
I can also provide the addressing table I created if it would be of use.
Thanks so much, learning networking feels extremely complicated

bhiter010 · January 2023

so...

you have 192.168.4.131 /30 to one port and 192.168.4.132 /30 for the other

router's ip 192.168.4.131 255.255.255.252 (mask 22!)

if you place new ip's in your subnet, you should use the same mask 22 in your case! (or /30)

try ip calculator it is very useful for understanding networks

https://jodies.de/ipcalc /

volfkhat · January 2023

a /30 subnet means that the "usable" ip range is:

.1 & .2
.5 & .6
.9 & .10
.13 & .14
...
.125 & .126
.129 & .130
.133 & .134
and so forth

If you don't really understand how this works... then you shouldn't bother trying to work on network gear.

Learn the "MAGIC number" technique:

then you'll be good to go!

VLSM Routing

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