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Home > Archive > CCNP > March 2001 > Question
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| krazzzzy 2001-03-22, 7:01 am |
| This might seem a lil strange, cause it did to me. At work we monitor Internet access, and one of our sites was constantly bouncing up and down. Over a 16hr period maybe 700 times. Initially we thought it was a clocking problem but it wasn't and one of the Engineers who had experienced the problem before changed the ip address on the serial port and it works. He really didn't go into detail with me about why changing an ip address on the serial port fixed the problem. Before he made the change we were getting slugglish pings and traceroutes with the old ip address but getting good pings to the ethernet port. I only thought the only time you'd have a problem with an ip address was if it was a duplicate on the same network, but that isn't the case. I work third shift by myself, so i don't get to see how many problems are resolved other than reading the trouble tickets from the days events. Anyone care to share a lil light? | |
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| Hi Krazzzzy,
You probably hit the nail on the head. It is possible that the IP address that the serial interface had might have been mistakenly assigned to another device. This other device might not have always been powered up or connected. When it
was it caused the duplicate ip address nightmare.
Checking the router's arp cache can tell you what
MAC's go with what IP's.
Best of luck
Danny | |
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| First of all, I think we would all benefit if we put more effort into descriptive topic lines. I am more likely to get the attention of the right people if my topic line indicates what kind of subject matter the thread is about. Personally I usually do not read threads with topic lines like:
"Question"
"Help"
"I need help"
and so on.
Of course I will sometimes miss an interesting thread like this one:
quote:
Originally posted by krazzzzy
This might seem a lil strange, cause it did to me. At work we monitor Internet access, and one of our sites was constantly bouncing up and down. Over a 16hr period maybe 700 times. Initially we thought it was a clocking problem but it wasn't and one of the Engineers who had experienced the problem before changed the ip address on the serial port and it works. He really didn't go into detail with me about why changing an ip address on the serial port fixed the problem. Before he made the change we were getting slugglish pings and traceroutes with the old ip address but getting good pings to the ethernet port. I only thought the only time you'd have a problem with an ip address was if it was a duplicate on the same network, but that isn't the case.
Since it's a serial interface ARP isn't used.
One possibility is that this is related to load balancing and a bad link somewhere else in the network. For increased capacity multiple T1/E1 links are sometimes connected in parallel and load balanced. Depending on the method of load balancing a packet may use one specific link for a given IP address. If that link is bad you may have a high packet loss when pinging the given IP address but not when pinging another. Changing IP address could cause the packets to travel on another (good) link. It doesn't help the bad link though.
Why don't you ask the engineer and tell us? We might actually learn something.
Have fun!
Terje | |
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| In troubleshooting this problem the first tools I would use is traceroute and with that saying I would have used the source and the destination which is very important when you are talking about a serial line.I would agree with response early that some where in data path a link is poorly performing or just plain down/down.Chosing another ip address simply rerouted the traffic.Now what I don't agree with early response is the fact that because this serial line the router will not have arp table.In my experience for example if I wanted know all directly connected on a leased line.I would simply do show ip arp which would show all corresponding routers with mac/ip address.The only situation in which you couldn't use arp I think if router doesn't accept arp request..but this just my opinion |
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