Smoothwall and ISP with /31 subnet

[mikeglover]

Hi all,

 

I'm curious to know if anyone has or had Smoothwall and an ISP that use a /31 subnet for router gateway.

Our ISP Exponential-E use a /31 subnet and Smoothwall say they can't use that.

I've got a installation of Smoothwall due soon and it's looking at the moment like we can't go with Smoothwall because of our ISP which is really frustrating.

Trying to get a reason from Smoothwall on why we can't and getting my ISP to move it to a /30 subnet seems impossible at the moment.

Wonder if anyone else has been through the same headache?

 

Mike

[PaddyNewman]

What are you currently connecting to it with? If its a L3 switch, use the Smoothwall behind that and route traffic through it... but no, I would expect Smoothwall to support that as its linux underneath and similarly would expect the ISP to support a /30 on the edge. Aren't expo-e just using a Juniper edge with your range routed to nexthop, nothing stopping the change to a /30...

[ibpalle]

Yeah, /31 is a problem for us as we expect a 'proper' subnet with broadcast and network address.

 

Just a thought but haven't tested it. Potentially, if you add the IP and gateway with a /30 and then manually add a static ARP mapping for the gateway device IP, it could work. The issue is that /31 breaks the broadcast and MAC address finding routines so a static MAC address mapping for the gateway IP might work.

[SchoolsBroadband]

It should be easy for Expo-E to give you a couple more IP addresses and make it to a /30. You might have to pay for them but it shouldn't be much

[mikeglover]

Hi all,

 

Thank you for your replies. I must admit my knowledge on this is a bit limited but I do understand that /31 being point to point I dont have broadcast address and something I guess smoothwall boxes are configured to rely on.

I've managed to speak to someone with knowledge at Expo now and hopefully have a plan. @PaddyNewman We currently have a Cisco Meraki MX firewall using /31 which is fine.

Our plan now is to temporarily have 2 connections into the school, our existing /31 and a new /29 subnet created that smoothwall will like. It will allow us to transition from Meraki to Smoothwall safely then terminate the /31 when we know we are safe.

Just waiting on installation dates now and work out downtime for the school. Things like SIP trunks will need be to timed to move when we move subnet.

I'll come back and let everyone know how it goes. :-)