Crystals with slightly difference specs with the microcontroller?

Hi, i'm currently trying to build an ethernet interface for my project.

I'm using a National Semiconductor DP83847 ethernet transceiver. The
data*** stated that it requires a 25Mhz 0.005% 50PPM oscillator.

My question is, lets say i can't find an exact match for the crystal,
such as:
1) Slightly lower/ higher frequency
2) Different accuracy, lets say 100PPM

What will be the effect for both cases?

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