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RE: Simple Ip issue (need help) [7:62728] posted 02/10/2003
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At 06:18 PM 2/10/2003 +0000, Priscilla Oppenheimer wrote:
>You can't have duplicate IP addresses anywhere. They have to be unique. The
>only exceptions would be if you were doing some sort of NAT or tunneling or
>something and the duplicates were hidden from each other.
>
>You don't get an error when you try to configure it because it's a lot
>harder for IOS to detect this on a serial interface than on an Ethernet
>interface. On Ethernet, a Cisco router ARPs for the address you give it. If
>it receives a reply, then it gives you an error and won't let you use the
>address. There's no ARP in serial land.
>
>You think you're pinging successfully, but how do you know who is really
>replying?
>
>Even if you could assign duplicate IP addresses, you shouldn't. You would
>wreak havoc with all sorts of things. There's no reason to do it either. If
>you're concerned with running out of addresses, just use private address.
>The 10.0.0.0 network has 16 million possibilities.

For what it's worth, duplicating the same IP across a set of DNS servers in 
the same AS can provide an interesting spin on resiliency.  So long as you 
configure unique IP's for normal communication.  This sort of thing works 
good for protocols that are stateless (UDP DNS)

Anycast-RP in PIM networks also uses the same IP on multiple boxes :-)

>Someone had to get blunt here! :-)

Someone had to split some hair !



>_______________________________
>
>Priscilla Oppenheimer
>www.troubleshootingnetworks.com
>www.priscilla.com
>
>
>
>
>Ladrach, Daniel E. wrote:
> >
> > If you ping you are probably pinging the Local IP.Try debug ip
> > icmp to
> > verify what you are pinging.
> >
> > Daniel Ladrach
> > CCNP, CCNA
> > WorldCom
> >
> >
> >
> > -----Original Message-----
> > From: Monu Sekhon [mailto:nobody@xxxxxxxxxxxxxx]
> > Sent: Monday, February 10, 2003 12:03 PM
> > To: cisco@xxxxxxxxxxxxxx
> > Subject: RE: Simple Ip issue (need help) [7:62728]
> >
> >
> > Hi All,
> > Thanx again for all for contribution
> > confusion still there ,
> > I am pinging remote side and I am able too.
> > any comments from all(still confused with answers)
> >
> > Walker, James - Is wrote:
> > >
> > > Only problem is which side are you pinging????????
> > >
> > >
> > >
> > >
> > > -----Original Message-----
> > > From: John Murphy [mailto:john.murphy@xxxxxxxxxxx]
> > > Sent: Monday, February 10, 2003 11:15 AM
> > > To: cisco@xxxxxxxxxxxxxx
> > > Subject: Re: Simple Ip issue (need help) [7:62728]
> > >
> > >
> > > If you're asking what I think you're asking, then I think your
> > > answer is
> > > yes, but you won't be able to pass any traffic across the
> > > circuit.  Unless
> > > you've confused me (it doesn't seem I would be the only one),
> > > then the
> > > answer might not be the same.
> > >
> > >
> > > ----- Original Message -----
> > > From: "Monu Sekhon"
> > > To:
> > > Sent: Monday, February 10, 2003 12:13 AM
> > > Subject: Simple Ip issue (need help) [7:62728]
> > >
> > >
> > > > Hi All,
> > > > I have very simple question, Can we use duplicate ips on
> > > serial interfaces
> > > > among them seleves although we cannot use duplicate ip on
> > > serial with
> > > > Ethernet(lan interface) or loopback interface.
> > > >
> > > >
> > > > My topology is like this
> > > >
> > > > Client router server router(connected back to back)
> > > >   2 interfaces           2 inetrfaces
> > > >
> > > >
> > > > these routers connected back to back
> > > >
> > > >
> > > > configuration
> > > > int serial 0/0
> > > > encap hdlc
> > > > ip address 1.1.1.1 255.255.255.0
> > > >
> > > > int serial 0/1
> > > > ip address 1.1.1.1 255.255.255.0
> > > > encap hdlc
> > > >
> > > >
> > > >
> > > > now if all the two interfaces of serial even if given
> > > duplicate ip among
> > > > themselves works fine. no error from cli .interfaces are up
> > > > and i am able to ping remote side.
> > > >
> > > >
> > > >
> > > > The ques is that
> > > >
> > > > 1) Lan interface also was in different subnet but serial
> > > interface
> > > > doesnot accept that ips as duplicate or of loopback
> > > >
> > > > 2)What Implication such have on my design ,any limitation it
> > > has
> > > >
> > > > Does this type of design can be used,
> > > >
> > > > This is small thing is confusing me about ip.
> > > >
> > > > Thanx  in advance




Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=62780&t=62728
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