Unusual Aspect of a duplicate IP Address [7:353]
Here is a scenario which caught me out BIG time in a real life situation using ISIS. To make it easier Router A has a serial connection to Router B Everything is up layer 1 & 2i.e CDP can indeed see Router B if you are on Router A and vice versa. Router B can't see any routes from Router A or beyond. NOW Routers A serial 0's ip address is 172.16.130.5, Routers B serial 0's ip address is 172.16.130.5. Spot the deliberate mistake. Although you say AHA he has the same ip address on the serial connections. SO, quite rightly ISIS says, go away I will never make an adjacency with myself :-( However, it took me quite a while to discover that these IP addresses were indeed duplicated. REASON or should I make it a question? I think question would be better. Q: What do you think would happen if I was on Router A and telnetted to 172.16.130.5, would I telnet to Router A or B. :-> A: This is why it took me a while to realise this. I started debugging adjacencies, blaming a new controller card which was the first time I had used this in ISIS, everything bar the easy problem. Mental Note for me here is don't dive in head first, always fault find the layers and remember this fault because it is nasty :-< What made it worse was the customer sitting over my shoulder saying WHY isn't this working, I knew we shouldn't have bought those new fangled router things! Oh the joys of life Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=353&t=353 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: Unusual Aspect of a duplicate IP Address [7:353]
At 01:09 PM 4/12/01, McCallum, Robert wrote: >Here is a scenario which caught me out BIG time in a real life situation >using ISIS. > >To make it easier > >Router A has a serial connection to Router B > > >Everything is up layer 1 & 2i.e CDP can indeed see Router B if you are on >Router A and vice versa. Router B can't see any routes from Router A or >beyond. > >NOW Routers A serial 0's ip address is 172.16.130.5, Routers B serial 0's >ip address is 172.16.130.5. > >Spot the deliberate mistake. > >Although you say AHA he has the same ip address on the serial connections. >SO, quite rightly ISIS says, go away I will never make an adjacency with >myself :-( > >However, it took me quite a while to discover that these IP addresses were >indeed duplicated. > >REASON or should I make it a question? I think question would be better. > >Q: What do you think would happen if I was on Router A and telnetted to >172.16.130.5, would I telnet to Router A or B. :-> I think I saw something similar today, though not with ISIS. But duplicate IP addressing caused us to Telnet to ourselves (i.e. Telnet from Router A to Router A.) Troubleshooting went downhill for a while until we figured out that was what was happening. Is that what you saw too? Thanks for the cool scenario. I hope the customer stopped breathing down your back finally. Priscilla >A: This is why it took me a while to realise this. I started debugging >adjacencies, blaming a new controller card which was the first time I had >used this in ISIS, everything bar the easy problem. Mental Note for me here >is don't dive in head first, always fault find the layers and remember this >fault because it is nasty :- >What made it worse was the customer sitting over my shoulder saying WHY >isn't this working, I knew we shouldn't have bought those new fangled router >things! > >Oh the joys of life >FAQ, list archives, and subscription info: >http://www.groupstudy.com/list/cisco.html >Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] Priscilla Oppenheimer http://www.priscilla.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=433&t=353 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: Unusual Aspect of a duplicate IP Address [7:353]
No, What I saw was while on Router A if I telnetted to the 172.16.130.5 address it took me to Router B, so I thought that everything IP wise was fine. On Tom's comment ISIS does require that IP is correct despite it using CLNS to form adjacencies. Try it and see, when attempting an adjacency do a debug isis adj and you will see a line saying no usable IP addresses to from an appropriate adjacency. However I thought that this scenario above would be protocol independent BUT Priscilla seems to have a different result with the same scenario. Cheers :-o -Original Message- From: Priscilla Oppenheimer [mailto:[EMAIL PROTECTED]] Sent: 13 April 2001 02:05 To: [EMAIL PROTECTED] Subject: Re: Unusual Aspect of a duplicate IP Address [7:353] At 01:09 PM 4/12/01, McCallum, Robert wrote: >Here is a scenario which caught me out BIG time in a real life situation >using ISIS. > >To make it easier > >Router A has a serial connection to Router B > > >Everything is up layer 1 & 2i.e CDP can indeed see Router B if you are on >Router A and vice versa. Router B can't see any routes from Router A or >beyond. > >NOW Routers A serial 0's ip address is 172.16.130.5, Routers B serial 0's >ip address is 172.16.130.5. > >Spot the deliberate mistake. > >Although you say AHA he has the same ip address on the serial connections. >SO, quite rightly ISIS says, go away I will never make an adjacency with >myself :-( > >However, it took me quite a while to discover that these IP addresses were >indeed duplicated. > >REASON or should I make it a question? I think question would be better. > >Q: What do you think would happen if I was on Router A and telnetted to >172.16.130.5, would I telnet to Router A or B. :-> I think I saw something similar today, though not with ISIS. But duplicate IP addressing caused us to Telnet to ourselves (i.e. Telnet from Router A to Router A.) Troubleshooting went downhill for a while until we figured out that was what was happening. Is that what you saw too? Thanks for the cool scenario. I hope the customer stopped breathing down your back finally. Priscilla >A: This is why it took me a while to realise this. I started debugging >adjacencies, blaming a new controller card which was the first time I had >used this in ISIS, everything bar the easy problem. Mental Note for me here >is don't dive in head first, always fault find the layers and remember this >fault because it is nasty :- >What made it worse was the customer sitting over my shoulder saying WHY >isn't this working, I knew we shouldn't have bought those new fangled router >things! > >Oh the joys of life >FAQ, list archives, and subscription info: >http://www.groupstudy.com/list/cisco.html >Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] Priscilla Oppenheimer http://www.priscilla.com FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=611&t=353 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]