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Layer 3 over 2200ft distance

I have an access Catalyst 3524 switch uplink to backbone Catalyst 6509 switch. The uplinks ports are LX-GBICs adaptors. The distance I believe would be about 2200 feet. The link ports on 3524 and 6509 are green and in up/up mode. I can also see the devices in CDP Neighbor commands, but I can't ping anything from 3524 to 6509.

Could it be a distance that doesn't allow layer 3 traffic to pass through eventhough I can see the devices in CDP as layer 2.



Re: Layer 3 over 2200ft distance

Distance is only a factor at Layer 1, the Physical Layer (your Ethernet). If you exceed the capabilities of the GBICs, then anything ou try to do across them can be impacted.

Can you get the 3524 and 6509 together in the same room, and perform the same ping tests? This will help isolate whether the problem is in the equipment, or the fiber.

Rule out the simple stuff first. Is there a Layer 3 interface defined on the 6509 for the VLAN you're trying to ping from? The management VLAN between your 3524 and 6509 would pass CDP traffic, but if you're pinging fom a different VLAN access port on the 3524 and there isn't a Layer 3 interface for that VLAN on the 6509 (or there is, but it's shutdown) then you're not going to get anywhere.

If it works in the same room, then you are going to have to get Physical...

Cisco LX/LH GBICs are rated to 10km (about 32,800 ft.) over single mode fiber, which is 5km farther than the LX standard calls for. Over multimode fiber, standard calls for LX to reach 550m (about 1,800 ft.), which is 400 ft. short of the distance you are working with. What kind of fiber are you using?

If multimode, you might be able to exceed the standard somewhat, if you have good cable to work with.

Are you using mode conditioning launch/patch cables? At your distance, you most likely need them.

Do you have access to an optical TDR, to check the dB loss of your fiber cable at 1300nm wavelength? Scan the cable span itself, then again end-to-end through the patch cables so you know what the GBICs will be dealing with. On the LX/LH have a 9.5-dB loss budget to play with. If your loss figures are higher, your options are drop back to 100BASE-FX over multimode (good to 2km in full duplex) or install single mode fiber to go Gigabit speeds.

I have pushed LX/LH GBICs out to 16km over single mode, and stayed within the dB loss budget for the GBICs. We ran our Internet connection over that for two years. (Dropped back to Fast Ethernet transport over the fiber because we were getting throttled to 10-meg at the ISP's end anyway, and we had better uses in-house for the Gigabit equipment.)

I have also tried to push LX/LH GBICs farther, that is, into ranges that obviously called for using ZX GBICs, just to see what would happen. I would always get a link light, and switch-to-switch pings seemed to work most of the time. Would see the neighboring 6509 in CDP. Telnet worked some of the time, but was not reliable, freezing up occasionally. Came to find out that it was due to our 3524 losing enough BPDUs that UplinkFast would cut over to using the alternate path back to the 6509 (a known good LX link, with more hops to go through so it wasn't the preferred STP path back to the root switch.)

Hope this helps.

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