[CentOS] Basic Network question pinging different subnets

Sat Nov 17 18:07:20 UTC 2007

On Nov 17, 2007 5:12 AM, Bob Metelsky <bobmetelsky at comcast.net> wrote:
>
>  Im a dba not a network guy... :)
>  Well.... ok I know there are technical "reasons" why this doesn't seem to
> "work"
>
>  But -  why can I ping any other ip address ....  ie Google
>  64.233.167.99

Because the routes, (  C:\> route print  ) say to send such packet to your GW,
that  know nothing about 10.54.0.0/24 and then follow its own route to
is own GW that do the same ...
Finlay nobody on the internet know about 10.54.0.0/24 and you never
get answered.
But Internet know about Google, that get the packet and answer.

If you teach your GW or your own computer for what to do with such
packets, they will reach their target
AND if the reverse way is well defined too you will get an answere.

>
>  Ok I guess thats "resolvable" and not private. My thinking is ping should
> try and  "find" the address
>
>  Maybe I need a type of local dns...(??)  How does one avoid  manually
> adding "routes"

No way, DNS don't configure route, you cannot break away

>
>  my port scanner - I give a range 10.54.0.0 - 10.54.7.55, Im thinking it
> should try all addresses in between and it only gets the ones on 10.54.7.0
>
>  The comment below sounds like what I need... thanks!
>
>
>  "
>  c:\> route add 10.54.0.0 MASK 255.255.255.0 10.54.7.16
>
> But this should give you access on both 10.54.0.2 and 10.54.0.3
>  "
>
>  C:\>route add 10.54.0.0 MASK 255.255.255.0 10.54.7.16
>
>  C:\>ping 10.54.0.2
>
>  Pinging 10.54.0.2 with 32 bytes of data:
>
>  Reply from 10.54.0.2: bytes=32 time<1ms TTL=64
>  Reply from 10.54.0.2: bytes=32 time<1ms TTL=64
>
>  My purpose is to have a private network between database servers (oracle
> rac) where only specific traffic is allowed, and it works that way, I was
> just surprised that I want able to ping the 0 subnet.

Dont forget IP protocol  and ETHERNET protocol are working together
here. You should know how.

>  So I need to add the route...
>
>  Thanks for everyones feedback. Hopefully I can contribute something....in
> the future
>  ;-)
>

Regards.

>  Bob
>
>
>
>
>
>
>  Alain Spineux wrote:
>  On Nov 17, 2007 1:25 AM, Bob Metelsky <bobmetelsky at comcast.net> wrote:
>
>
>  Hi Im a little perplexed by this situation
>
> I have centos 4.5 installed on 2 pcs - each with 2 network cards
>
> machine 1
>
> eth0 Link encap:Ethernet HWaddr 00:14:2A:6B:C8:CC
>  inet addr:10.54.7.2 Bcast:10.54.7.255 Mask:255.255.255.0
>
> eth1 Link encap:Ethernet HWaddr 00:11:50:9B:A2:90
>  inet addr:10.54.0.2 Bcast:10.54.0.255 Mask:255.255.255.0
>
> machine 2
>
> eth0 Link encap:Ethernet HWaddr 00:14:2A:69:4C:47
>  inet addr:10.54.7.3 Bcast:10.54.7.255 Mask:255.255.255.0
>
> eth1 Link encap:Ethernet HWaddr 00:11:50:9B:A5:0A
>  inet addr:10.54.0.3 Bcast:10.54.0.255 Mask:255.255.255.0
>
>
> machine 1 & 2 can ping each other on either subnets
>
> machine 3 (windows)...
>
> C:\>ipconfig
>
>  Connection-specific DNS Suffix . :
>  IP Address. . . . . . . . . . . . : 10.54.7.16
>  Subnet Mask . . . . . . . . . . . : 255.255.255.0
>  Default Gateway . . . . . . . . . : 10.54.7.1
>
> cant ping anything on the 10.54.0 subnet, nor does that subnet show up
> ip using a port scanner...
>
> C:\>ping 10.54.0.2
>
> Pinging 10.54.0.2 with 32 bytes of data:
> Request timed out.
> Request timed out.
>
> C:\>ping 10.54.7.2
>
> Pinging 10.54.7.2 with 32 bytes of data:
> Reply from 10.54.7.2: bytes=32 time<1ms TTL=64
> Reply from 10.54.7.2: bytes=32 time<1ms TTL=64
>
>
> Any ideas why this is happening? I dont have a firewall on the 10.54
> address,
>
>  Yes ! You have to learn how works IP networks :-)
> IP is wild and wide :-)
>
> you can try this on your windows :
>
> c:\> route add 10.54.0.2 MASK 255.255.255.255 10.54.7.2
>
> OR
>
> do the same on your router at 10.54.7.1
>
> OR (depend on how your linux box is configured)
>
> c:\> route add 10.54.0.0 MASK 255.255.255.0 10.54.7.16
>
> But this should give you access on both 10.54.0.2 and 10.54.0.3
>
> OR if routing is enable on 10.54.7.2
>
> c:\> route add 10.54.0.0 MASK 255.255.255.0 10.54.7.2
>
> should also give you access to both 10.54.0.2 and 10.54.0.3
>
>
> You just have to understand the first one other are just to spread out
> my IP knowledges.
> Ops, the last one is sometime useful to configure a device on another
> IP range, without reconfiguring your IP.
> Like when unpacking a new router with IP 192.168.123.1
>
> Regards.
>
>
>
>
>  Thanks
> Bob
>
>
>
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-- 
Alain Spineux
aspineux gmail com
May the sources be with you