Problem routing to a cisco loopback address of *.*.*.255

  • Thread starter Thread starter Wazza
  • Start date Start date
W

Wazza

Anyone come across a problem routing from windoes 2000 to a cisco loopback
address od *.*.*.255, Windows thinks that it is a broadcast address and
refuses to route it.

TIA

Wazza
 
Wazza said:
Anyone come across a problem routing from windoes 2000 to a cisco loopback
address od *.*.*.255, Windows thinks that it is a broadcast address and
refuses to route it.
Click to expand...

Which netmask do you use on loopback? If it's not a /32, you shouldn't use
that address...

Ivan
 
Which netmask do you use on loopback? If it's not a /32, you shouldn't
use that address...

Ivan
Click to expand...

I will try and make this clearer.

There is a router on the network with a loopback address of "*.*.*.255",
i can ping that ok from unix servers, but win2k servers wont. I can ping
"*.*.*.254" from both unix and win2k. Win2k seems to be making a decision
not to allow any traffic to "*.*.*.255". Is this "special" as far as
windows is concerned? Is there a setting i can change to allow traffic to
route to *.*.*.255?

Cheers

Wazza
 
I would configure that loopback address to be something else, anything but *.*.*.0 or *.*.*.255.
Then, as Ivan said, put a /32 (255.255.255.255) mask on it.. Make it a different subnet than the
network your Unix and Win2k boxes are on.. As long as they have the correct default gateway, they
should be able to hit it.. I've done this same setup at home...

I would bet your successful pings from your Unix box aren't getting to your router's loopback, they
are getting to the broadcast IP for your subnet, with success! ;-) And your Win2K box is actually
being wiser in this case, saying "Hey, why would I want to ping a broadcast IP anyway??" ;-)

: "Ivan" <[email protected]> scribbled in
:
:> :>> Anyone come across a problem routing from windoes 2000 to a cisco
:>> loopback address od *.*.*.255, Windows thinks that it is a broadcast
:>> address and refuses to route it.
:>>
:>
:> Which netmask do you use on loopback? If it's not a /32, you shouldn't
:> use that address...
:>
:> Ivan
:>
:>
:>

: I will try and make this clearer.

: There is a router on the network with a loopback address of "*.*.*.255",
: i can ping that ok from unix servers, but win2k servers wont. I can ping
: "*.*.*.254" from both unix and win2k. Win2k seems to be making a decision
: not to allow any traffic to "*.*.*.255". Is this "special" as far as
: windows is concerned? Is there a setting i can change to allow traffic to
: route to *.*.*.255?

: Cheers

: Wazza
 
There is a router on the network with a loopback address of "*.*.*.255",
i can ping that ok from unix servers, but win2k servers wont. I can ping
"*.*.*.254" from both unix and win2k. Win2k seems to be making a decision
not to allow any traffic to "*.*.*.255". Is this "special" as far as
windows is concerned? Is there a setting i can change to allow traffic to
route to *.*.*.255?
Click to expand...

Is there anything in the configuration that would make it think
"*.*.*.255" is in a /24 network?
 
Is there anything in the configuration that would make it think
"*.*.*.255" is in a /24 network?
Click to expand...

We're grasping at straws here, you haven't provided enough information
to get any concise help.

I'll grasp anyway though...

To my knowledge Unix and Windows do not stop you from pinging the
broadcast ip address unless that machine (Unix or windows) knows
specifically that the ip you are trying to ping is a broadcast ip. The
only way that would really be is if the server were physically on that
network. For example, I have a redhat server on 10.0.0.0 /24. The
broadcast on that network is 10.0.0.255 and if I try to ping it I must
put in the "-b" flag to indicate that yes I do want to ping the
broadcast ( I don't think windows does this or cares if you ping the
broadcast). In such a case I would get a response back from every
device on that subnet. Well, lets look at another example. 10.0.0.0
/23, the broadcast there would be 10.0.1.255 not 10.0.0.255.
10.0.0.255 would be a perfectly valid ip address to use as it is in
the middle of the subnet. As would be the case if you used 10.0.0.0/32
as a loopback address - there should be no problem with that as it is
a perfectly valid single ip subnet per the VLSM rules. Just the same,
as stated earlier by someone else - *.*.*.255/32 is a perfectly valid
single ip subnet that would be just fine to use and route as a
loopback address.

Are the UNIX servers you're speaking of on the same subnet as your
windows 2k servers?

What is the exact configuration of that loopback and it's
corresponding routing entry?

for example
loopback0
ip address *.*.*.255 255.255.255.255 ?

router ospf 1 <--assuming ospf
network *.*.*.255 0.0.0.0 area 0?

Also, showing a routing entry from a neighbor router might help too -
maybe you have a routing issue.

Also, if the UNIX and W2K servers are on the same subnet - compare
their configurations - make sure they are itentical (with the
exception of the actual IP assigned to each of course).

Good luck.

The Mikester
 
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