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Routing, network cards, OSI, etc. Anything is fair game.
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Does /31 subnet mask support really exist in Linux? FYI, I am using the linux version 2.6.34.
As part of my trails, I have two linux boxes connected back to back. I am able to configure the interface addresses with a /31 netmask viz., 192.168.10.4 and 192.168.10.5 successfully. 'ifconfig' output confirms that. But I am not able to ping the other address from 192.168.10.4 and vice-versa.
So, I just doubt if this is really supported? If yes, Am I missing something?
i've always configured 2 host subnets as /30's then there's no conceptual issue here. I'm actually not sure whether a /31 subnet is meant to work according to RFC's (potentially regardless of reality). Does it work on a /30? (shifting the hosts up by one to fit nicely) Can you see any arps coming or going from a tcpdump?
I would say that if it works, congrats, but don't be at all surprised, or annoyed, if it doesn't. I just skimmed over the RFC from 2000 advocating it, and I don't like the idea of it outside of IP space conservation. Can you not use a /30?
Last edited by acid_kewpie; 01-20-2012 at 07:45 AM.
Thanks for your response, Chris. That was helpful.
I am in a necessity to work with /31's as part of my project work. It looks like it works with /30's. With /31's, I don't see any ARPs coming out on the wire. When we configure an interface with a /31 address one end of the link is a broadcast address. Is it because of some validations in the linux kernel code concerning the broadcast addresses that is preventing the (ARP/IP) packets to be sent out? If so, do we need to customize the kernel code to achieve this? Has anyone achieved success in making the /31's work?
We're using /31 on all link networks between Cisco routers - directly connected as well as for IP tunnels. It works well and doubles the ammount of available link networks, which is good in respect to IPv4 depletion. So I would be pleased if it works on Linux too. Does anybody have any experience with it?
The key here is the the following:
ifconfig eth0 pointtopoint <IPADDR>
This seems to work however I'm trying to work out how to hard code it...
I noticed via tcpdump without the above the interface will receive the traffic however the network stack doesn't seem to know how to send packets back.