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RE: WinXP and Valhalla machines do not respond to each other's ping's

Keith, Thanks for clarifying Phil's bizarre subnet mask layout. Did not make
sense to me.
I guess if you are the mighty "Cable Company", you can implement whatever
network layout you want. Seems like they might have one flat Class A address
space in Phil's situation and use some sort of "IP to MAC layer translation
table" Bridging hardware to handle the routing of packets down their various
community feeds.
At least I hope they dont just broadcast all Internet incoming packets down
local feeds.

Know of any good web sites that deal with Cable Modem network topologies?
My curiosity is peeked.........

I am just installing Cable Internet at my home and I am fronting it with a
Netgear VPN Firewall.

My recommendation to Phil is to use a Netgear or Linksys firewall instead of
Valhalla box. Let Vahalla act as a server instead of a
The Home firewalls are cheap enough and probably run a stripped Linux OS.
Or at least use a separate stripped down linux box as a firewall only.

I would still enable the firewall on Valhalla just for it's own protection.
More comments below.

> -----Original Message-----
> From: valhalla-list-admin redhat com
> [mailto:valhalla-list-admin redhat com]On Behalf Of Keith Mastin
> Sent: Tuesday, April 22, 2003 3:58 PM
> To: valhalla-list redhat com
> Subject: RE: WinXP and Valhalla machines do not respond to
> each other's
> ping's
> > figure out why they are different. Neither mask makes sense
> based on the
> > two ip addresses you provided. If you are using DHCP on
> both boxes and
> > the webstar is supposed to be providing all the
> information, then the
> > subnet masks should be the same.
> The set up looks like the ISP is providing the configurations
> for both and
> the webstar is just forwarding the information along. It also
> looks like
> the modem is not routing as opposed to forwarding. This would
> explain the
> different IP subnets, subnet masks, etc.

Are there any cable modems that do routing? Most of the ones I have seen
are just simple pass through bridging devices like analog modems and you get
to map
to their MAC address. I know Cisco has a low end unit that is a combo Cable
Modem, router,
and firewall type setup designed for SOHO use. I guess time to do a search
on cable Modems
and get a handle on those varmints. I am curious to see if the cable modem
acts as a MAC layer bridge.

> > based on the addresses provided, you would normally have a
> subnet mask
> > of for a Class A address. They may be subnetting
> into part of
> > the second octet. 255.128, 255.192 depending on if they chop up the
> first > two bits. You would have to convert the two addresses
> to the HEX
> > equivalent of each octet to see where the Network mask
> might end, but the
> > ISP should have provided this information or the Cable
> modem should have
> > it set since it would normally pick it up from them via
> I know that the cable company here in Toronto uses mac addressing and
> allows 2 connects, and the dhcp designations can look just as
> fubar'ed as
> the one's that Phil has shown here.


> > OR worst yet, one of your IP's is coming from out of left field from
> > another source.
> > IE. One is not from your ISP or is an old address. Has all this
> > equipment been recently rebooted? You might want to turn it all off
> > (except for hub), power up the cable modem and then each
> system in turn
> > and see what the IP/subnet masks get reset to.
> I would venture a guess that they'll be just as diverse.

You are probably correct, It also means there is no quick fix to his problem
without isolating his subnet from their networking topology and using a NAT
I was hoping it was a quick "fix the subnet masks" solution.

> > 1) Find out what the webstar/DHCP source server thinks it is setting
> > them to. Its usually via a provided cdrom snmp based
> windoze program or
> > web based interface
> >
> > 2) check your ISP's provided doc or tech support to find
> out what they
> > should be set to.
> >
> > 3) Check the network configs of all windoze/linux boxes to make sure
> > they are really set for DHCP.
> Hmm... if the modem isn't routing and has no firewall
> configuration (the
> webstar Dxl-100 docs don't suggest it's doing either), then
> the chances of
> the 2 machines being able to talk to each other are slim. The
> ping test
> should pass, but if both machines have the default gateway
> set to the ISP
> and the ISP is blocking icmp type 0 packets, there would be
> no response
> anyway. Blocking icmp type 0 doesn't make any sense though,
> especially on
> a dhcp assigned network.

But shouldn't his ISP/"aka cable company" be routing the packets for him
from one system to the other
if they are on the same ISP network? I would think so. The packets would
have to travel
up the cable to the central office and get routed back down from there. We
know each
system can see the Internet. I wonder if his ISP/Cable company can
reconfigure something
at the central office to fix his issue and allow peer to peer

> I think Phil's best bet here is to set up the valhalla
> machine as a NAT
> router and issue rfc-1918 ip assignments. It's more secure,
> less headache
> and more flexible than the present situation.

I would suggest a separate firewall such as Netgear's or Linksys for

> --
> Keith Mastin
> BeechTree Information Technology Services Inc.
> Toronto, Canada
> (416)696 6070
> _______________________________________________
> Valhalla-list mailing list
> Valhalla-list redhat com
> https://listman.redhat.com/mailman/listinfo/valhalla-list

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