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Giga port on WS 4418-Gb module


I Saw on the configuring Ws 4418 gb network module paper that the port 3-18 are note recommended to connect SWITCH or Router ..

Can you explain to me why ..

If I connect a switch that use Isl encapsulation on it what will it happend ??

Thank you

Cisco Employee

Re: Giga port on WS 4418-Gb module


"Ports 1 and 2 on the 18-Port Gigabit Ethernet switching module are fully independent, nonblocking Gigabit Ethernet ports. Ports 3 through 18 are oversubscribed, which means that the ports may have a limit on the amount of data they can receive without dropping packets. The circuitry for ports 3 through 18 is multiplexed in four groups of four ports each:

Ports 3, 5, 7, 9

Ports 4, 6, 8, 10

Ports 11, 13, 15, 17

Ports 12, 14, 16, 18

To help identify the groups, the front panel of the 18-Port Gigabit Ethernet switching module has lines that frame the port groups

The four ports within each group use common circuitry that multiplexes the group into a single, nonblocking, full-duplex Gigabit connection to the internal switch fabric. For each group of four ports, received frames are buffered and fed to the common Gigabit Ethernet link to the internal switch fabric. If the amount of received data for a port begins to exceed the buffer capacity, flow-controlled frames (pause frames) are sent to the port's linked device to temporarily stop traffic and prevent frame loss."

So based on that, if you connect trunk ports to another switch, you stand the chance of dropped packets due to buffer overflows. If you use just one port out of the block of four, then you should be fine, but they are designed to be host ports, rather than trunk ports.

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