Why cant my Linux server communicate with my local PC's on the same subnet?

Question

I have a Linux Server I have built with Centos 5.2 to be my localized file server. It will eventually be setup to share a volume accessed from my LAN from both PC's and MACs through a samba share. I need to be able to SSH into it from outside and I have that configured on the box and it is working in certain situations I already know since I’m behind a PIX 501 I will have to setup natting to redirect the outside address to the inside address with the specific ports for which I need to access these services depending on where I’m going with it. Since I’m going to be using dyndns.org on my router, those requests will be routed in to the 192.168.8.1 only, while anything dealing with ports 22, 23, 21, and others on the Linux box, I want only to go to that box 192.168.8.100 for higher security.

My cable modem comes into the pix and it goes from the pix to my Linksys wireless router. all of my pc's are wireless with the exception of my Linux box which plugs into the wireless router (Linksys WRT54GL) ok so I want to give my Linux box a 192.168.8.100(static) my wireless stuff is on DHCP leases from 192.168.2 - 11 with 192.168.8.1 being the address of the wireless router or the Default Gateway. I had originally setup the Linux to 192.168.8.100 with a class c subnet mask and 192.168.8.1 being the gateway however with the wireless being leased and the Linux box static they would not talk over SSH, I could not ping from either Linux to pc or from my pc to the Linux and I could not pull up Google. If I set Linux to DHCP it pulled 192.168.8.6 and everything worked fine, even if I set it statically to 192.168.8.6 which is within the lease range.

Just today I was thinking that maybe the default SPI firewall on the Linksys was blocking it. It is on and I have these options set: block anonymous internet requests, filter multicast, and filter IDENT (port 113); I have Filter Internet NAT redirection off. I have not tried turning off the firewall as of yet can someone advise me to whether this is the cause of my issues? I am behind a PIX in default state as of right now which I have not configured yet. So turning it off probably wouldn’t be a big deal

Answer 1

--EDIT: addition-- Sorry, I saw, "192.168.2 - 11 with 192.168.8.1" and thought "different subnets".. After re-reading your post, I realized, I've seen this same problem with linksys routers. Best way is to setup a static DHCP lease for your Linux box, in the linksys... Or make a BIG DHCP range, and statically set your linux box in the TOP of that range, so its IP is unlikely to get doled out by the linksys.



I think the bottom line is, the linksys doesn't like clients it didn't send out the DHCP for...

Answer 2

Thomas, I expierenced the same issue when setting up the Linksys NAS200 on my home network. I found that the NAS was only accessible outside if I had Filter Internet NAT redirection disabled. You have done the correct thing in leaving this option out, the SPI firewall won't effect the matter however tweaking VPN may make a difference it did for me. I have mine setup like so:



IPSec Passthrough, PPTP Passthrough, L2TP Passthrough - Disabled

Filter IDENT Port 113 - Enabled

Filter Multicast - Enabled

Block Anonymous Internet Requests - Enabled

Filter Internet NAT Redirection - Disabled



Addtionally my Linksys router is my DHCP provider, and I have TCP port 23 enabled on port forwarding & port triggering to connect to my NAS at IP 192.168.1.108, just incase I decide to access this anywhere from the world.



I suggest leaving DHCP enabled and setting a static IP for just the Linux Server, ensure you set up port forwarding & port triggering so this can be access via the Internet, this may also resolve internal issues you may be having.



Also bear in mind that if you have any 3rd party firewall installed you may need to enable the NetBios port to communicate between your PC's and Linux Server, try disabling your firewall to see if this may be the root cause. As long as your router is configured as above there should be no issues.

Answer 3

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