DEC VAX TCP/IP 1

[dentarthurdent]

I'm not sure if this is the right forum for this question but here goes.
I have a dec alpha box running VMS. Machines on the same subnet can ping it but PC's on a slightly different subnet can't.
IP=192.168.33.12
Mask=255.255.254.0

PC's on 192.168.33.xxx can ping it. PC's on 192.168.32.xxx can't. All masks of all machines set to 255.255.254.0.
There is no physical networking reason why they can't see the box. All other machines can see both subnets, it's just the VAX that can't.
Can anyone shed any light?

 

[johnny99]

To make sure that I understand it right.
You have one network 192.168.32.0 / 255.255.254.0

Hosts on 192.168.32.0 - 192.168.32.255 can ping each other.
Hosts on 192.168.33.0 - 192.168.32.255 can ping each other.
Hosts on 192.168.32.0 - 192.168.32.255 can't ping hosts on
192.168.33.0 - 192.168.33.255
Hosts on 192.168.33.0 - 192.168.33.255 can't ping hosts on 192.168.32.0 - 192.168.32.255.

On situation you would get this result is if the netmask used is 255.255.255.0 and not 255.255.254.0
What could be the problem for you (since you use 255.255.254.0 as your netmask) is that your IP-stack only supports classfull netmasks.

Check that your ip-stack supports CIDR. If not, changing your network to eg. 10.2.0.0 / 255.255.254.0 could solve your problem (or just using 10.2.0.0 / 255.255.0.0)

I don't know anything about your operating system, but I have seen the same problem on a Unisys ClearPath machine running MCP/AS

/johnny

 

[BradSQLGuy]

It's because with a mask of 254 that puts 192.168.33.x and 192.168.32.x on different networks. If you want them to both be able to communicate with eachother you need to set them as 192.168.34.x. Then you should have no problem pinging every single PC. 192.168.35.x is also going to be on a different network. Here is how you figuare it out. There are 8 bits in each octet of an address (octet=x x.x.x.x). Those are going to be 1, 2, 4, 8, 16, 32, 64, and 128. Mathematically if you have a subnet mask of 254 you need to add those up in binary until you reach 254. 254 in binary takes up 7 bits (128+64+32+16+8+4+2=254). The lowest number you have to use to add up to that subnet is how you add your addresses. Since the lowest number you use is 2 that is the increment at which you add (1-2,3-4,5-6,7-8,9-10,11-12, and so on until you reach 255). Each segment is a separate network and cannot see eachother. Once you reach 32 you will realize that it does not fall on the same network. Did that help or confuse? heh. -Brad
A+, MCSE NT4, MCDBA SQL7

-Best cartoon of all time :-D 'Spongebob Squarepants' :-D

 

[dentarthurdent]

Johnny, I think you might be onto something there. I remember reading that support for cidr was only introduced fully in a late version of VMS, not the ancient software I'm using.
I'm not sure I understand Brad's explanation as my netmask calculator (I can't do this in my head !) says that a client with IP 192.168.33.12 SM 255.255.254.0 should be able to see from 192.168.32.0 to 192.168.33.255. Besides, all my other clients can see this range, it's just the VAX with the problem.

 

[johnny99]

I think what Brad is saying is that dealing with subnetmasks you always have to make sure that you "cut" the network where you realy intend to.
I haven't calculated if he is right or not, but I would say that if you supernet two /24 networks to get one /23 network all 3. octed networknumbers that are even should work. And since the 3. octed of 192.168.32.0 is event I would think that it should work.

Remember to check all hosts that they have the right subnetmask

/johnny