Possible issues to consider using a 192.168.0.0/22 subnet

[Derrikdjc]

I have a customer who has an ASA 5505 that is handling the routing for their internal network. They are running out of available IP addresses on their subnet 192.168.1.0/24. They have dumb switches that don't suppport multiple vlans or trunking & they are only able to connect to one switchport on the ASA. He doesn't not want to purchase any new equipment or rearrange their existing equipment at this time. The customer would like to statically assign IP addesses for 192.168.1.x & 192.168.2.x and have the ASA hand out DHCP addresses for 192.168.3.x addresses. The customer suggested configuring a super subnet. A 192.168.0.0/22 address scheme would provide an ip range 192.168.0.0 - 192.168.3.255 on a single VLAN. I know this is an unconventional way to setup an internal network & I will definitely advise the customer that this should only be considered as a temporary solution until they get more appropriate network equipment. I wanted to know if anyone could tell me any issues or concerns I should warn the customer about having this type of setup.

[Raju Sekharan]

It depends on the amount of broadcast from the devices in the netwrok

Any broadcast in the network will reach to every hosts in the same broadcast network and it has to process it

1. Switches has to forward the extra broadcast and foward it through each link. So link bandwidth also utilized

2. Each host to process the broadcast even if it is not destined to it

[Richard Burts · Accepted solution]

I ran into this situation at a customer site. They were doing the same kind of thing with 192.168 networks defined with a /22 mask to get more address space. What we ran into is that some devices had an OS that would not accept the default gateway if it was outside of the logical /24 where their address was assigned. As I remember this device was a video device but I suspect that there are several OS where this would be a problem.

Just to be clear about what I was telling - assume that the network is 192.168.0.0/22. They were configuring a device something like 192.168.2.16. Their gateway was 192.168.0.1 and this device would not work with that gateway. They wound up assigning the device 192.168.0 52 and it worked fine.

HTH

Rick

[Derrikdjc]

Thank you both for your input.