Thanx all for giving information But I would like to clarify that I was pinging remote side and I was able too and i checked debugs also on both side. IP Packets are going successfully through the link. But why IOS doesnoyt give error , dont know the reason for that. anyway thanx I think nothing more input anybody can give so closing this issue.If still anbody wants to share some idea can do so . Thanx once again. Peter van Oene wrote: > > At 01:20 AM 2/11/2003 +0000, Priscilla Oppenheimer wrote: > >No problem with the splitting of hairs. :-) > > > >I have been wondering why Cisco lets you do what the original > poster is > >doing, which most of us misunderstood. He is using the same IP > address on 2 > >serial interfaces on the SAME router. > > Sonet APS comes to mind? I usually use a /29 with 4 addresses, > but you > could use the same address. > > >If you try to use the same IP address on two Ethernet > interfaces, you just > >get an error when you try to configure the second Ethernet > interface. > > I can't think of a practical use for this myself. > > >With two serial interfaces, you don't get an error. Is this > just an > >oversight? There are many such oversights in Cisco IOS. :-) Or > maybe there > >is a real reason to do it. > > The more I think about it (over the last two paragraphs of your > msg) the > more APS seems the likely candidate. If you couldn't, this > would be > restrictive in some cases. Of course I'm thinking APS capable > interfaces. > > >I said in my original message that there's no ARP on serial > interfaces so > >the router can't easily figure out if anyone else is using its > address like > >it does on Ethernet. On Ethernet the router can send an ARP to > see if > >someone else replies. But that's someone else on the LAN > connected to the > >interface, not another interface on the same router. > > > >So, if it gives you an error on Ethernet when you use an > address you have > >already used on another Ethernet interface, why doesn't it > give you an error > >for serial interfaces? Maybe there's an actual technical > reason, although > >probably it's just an oversight. > > > >By the way, it lets you configure an Ethernet interface to use > an address > >already in use on a serial interface, but if you try to do it > in the other > >order then you get an error. That's probably just another > oversight. > > Would agree here. Might be something to do with internal > mechanisms to map > macs to IPs. Ie, if an interface is added, check the mac/ip > binding list > for duplicates and error if there is one. Such a mechanism > wouldn't be > relevant in SONET and for the APS reasoning, it may be expected > that some > interfaces share the same address. > > >Cisco has always given you enough rope to hang yourself. > Decent error > >messages have never been any more important than ease-of-use. > :-) > > > >Priscilla > > > >Peter van Oene wrote: > > > > > > 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:[EMAIL PROTECTED]] > > > > > Sent: Monday, February 10, 2003 12:03 PM > > > > > To: [EMAIL PROTECTED] > > > > > 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:[EMAIL PROTECTED]] > > > > > > Sent: Monday, February 10, 2003 11:15 AM > > > > > > To: [EMAIL PROTECTED] > > > > > > 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 > >
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