What could cause this packet loss? 75% loss

[xSauronx]

I do a work study program with the network admin at the CC I attend, and he left me a task while he ran some errands today.

We have a 4507 catalyst as the core switch for the campus. Theres also a 3x50 (cant remember if its a 36 or a 37) switch that provides connectivity between a few rooms for the Early College High School and the local county school system. These switches are not connected in any way at all.

He wanted me to configure an 1841 router to go between those switches with a couple of static routes so that one POS system on campus can access the schools network for some updates or some such.

So I configure the routes, plug in the router between the switches to get this

POS --- CC network --- CC 4507 -- (10/100) -- 1841 -- (10/100) -- 3x50 --- (10Mbit something) --- county school network

from the 1841 I can now ping the county networks gateway without a problem
i can ping from the 1841 to the 4507 but only get intermittent responses.
i can ping the 1841 from a workstation on the CC network but get 75% packet loss
running debug ip icmp on the 1841 it shows that its replying to all the pings from the workstation, but still the workstation is only getting a response 25% of the time.

what can cause this? since i obviously have no access to the 4507 and the admin wasnt around for me to ask, and i guess we'll tinker with it tomorrow if he doesnt sort it out today, but im curious as to the possibilities

i used different patch cables between the 1841 and the 4507, didnt change anything (patch cables id used before without a problem).
i set up a couple of pc's and put the router between them, i can ping anything without issue.

 

[spidey07]

Start at layer1 - most likely a duplex mismatch between the 4500 and 1800. Or a bad cable. Make sure the switch AND router port are set to autonegotiate or speed and duplex are hard set, both MUST be either forced or auto. One side auto, other side hard set = duplex mismatch and crap loads of packet loss.

I'd bet 100 bucks on duplex mismatch, but you need to give me 20-1 odds for doing it blind.

If you want to test, test the router port at auto, 100/full and 100/half. That will tell you how the other side (4500 switchport) is configured.

 

[xSauronx]

oh i forgot to mention the FDX lights are lit up on both router interfaces. is there any case where theres some kind of duplex mismatch (like auto/full) where it would still light up?

 

[spidey07]

I'm concerned with the link between the 4500 and 1800 because that's what I saw you were having the problem with. How is the router interface configured?

 

[xSauronx]

Originally posted by: spidey07
I'm concerned with the link between the 4500 and 1800 because that's what I saw you were having the problem with. How is the router interface configured?

he said the 1800 was pretty much defaulted, so i just set the ip address/mask and brought the interface up, then added the routes, since thats all he asked me to do. i didnt check the running-config (oops? :Q)

 

[Cooky]

There could be a bunch of reasons why you get intermittent drops here...we'll need config from each device, and maybe some show outputs to determine the exact cause.

I'd start w/ layer 1 as spidey has suggested.
If it's not duplex or physical issue, check your routing - if multiple static routes, but only one is correct, it'll round-robin between them, and only the packets going across the correct path will go through.
Also check CPU utilization...what do you get when you do show proc cpu history or show proc cpu sorted?
How about spanning-tree, is it stable?
If you have 3750's that support layer 3 routing, why do you even use a 1841?
Those ISR routers don't support line rate.
Start pumping enough traffic through, and you'll see packets dropped, especially if you configure a bunch of services.

 

[xSauronx]

Originally posted by: Cooky
There could be a bunch of reasons why you get intermittent drops here...we'll need config from each device, and maybe some show outputs to determine the exact cause.

I'd start w/ layer 1 as spidey has suggested.
If it's not duplex or physical issue, check your routing - if multiple static routes, but only one is correct, it'll round-robin between them, and only the packets going across the correct path will go through.
Also check CPU utilization...what do you get when you do show proc cpu history or show proc cpu sorted?
How about spanning-tree, is it stable?
If you have 3750's that support layer 3 routing, why do you even use a 1841?
Those ISR routers don't support line rate.
Start pumping enough traffic through, and you'll see packets dropped, especially if you configure a bunch of services.

theres pretty much no way i can get the config on the core switch. i could get the one on the router tomorrow if he doesnt get it solved before i leave, for whatever thats worth (not much, i realize, but it is what it is)

theres only 2 static routes on the 1841, and nothing else. i can connect 2 pcs s to it and ping both pcs and both router interfaces without a problem, so im not sure i understand how it can be a routing issue on the 1841. can you explain?

if it helps:

my workstation is on vlan 110 (ip 192.168.110.70/24), through a switch somewhere that goes to the 4507.
the router fa0/1 is 192.168.110.5/24 and is connected directly to the 4507 fa 5/5
i have no way of knowing what the config is on that port, but the admin said it was unused and he didnt configure it at all except that its on, basically.

 

[Emulex]

bust out the console cable

doesn't everyone still leave serial console unprotected?

 

[xSauronx]

yeah we havent played with it anymore, not a high priority. i asked him what else there was to do and he wanted to have me setup a pix 501 to try instead....which got me nowhere because i dont know how to set up the pix *shrug*