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Several years ago, I purchased a Catalyst 4506 at a business liquidation, and it's been merrily humming along running my office network (I know it's tremendous overkill, but as I was the only bidder on it, it was only $75 in 2010).

It came with Supervisor IV, and two WS-X4148-RJ 48 port 10/100 line cards. It also came with some other cards with GBICs, but I've never used those.

Anyway, thus far, I've been able to teach myself enough to make it work for everything we need, including updating the system over TFTP, and I added a WS-X4248-RJ45V PoE card.

Recently I decided to look into adding a WS-X4448-GB-RJ45 48-port 10/100/1000 card, but it says that the GB bandwidth is shared with 8 ports. I can't find a descent description of the consequences of this. From what I gather, essentially only one port can use the full 1Gb at a time through the fabric, but what happens if two ports in the same block are communicating (like 1 <-> 2 @ 1Gb), do they get full speed?

Also, if several ports in a single block are trying to push 1Gb, what is the effect on the speed? Are they all throttled to like 1/n, or do they take turns at 1Gb? I could see this having consequences for VOIP, so I want to make sure.

I'm not keen on upgrading to a 4506E, since I doubt I can find one for $75.

Thanks!

crc32
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1 Answers1

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It's just device oversubscription. The ratio of oversubscription on that particular module is 8:1. So in industry terms, it's a "blocking" switch, versus a "non-blocking" device.

See this document from Cisco explaining the blocking ratios. The ports are grouped 1-8, 9-16, and so forth.

The better question is whether you're continually pushing Gigabit-speed traffic. You're likely not doing so in your scenario, so it probably doesn't matter. You can arrange high-traffic devices on different groups of ports to mitigate any issues, though.

ewwhite
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