if I type ifconfig eth0, it shows the following

$ ifconfig eth0

eth0 Link encap:Ethernet HWaddr b8:ac:6f:0c:7e:7e
inet addr:203.237.53.103 Bcast:0.0.0.0 Mask:255.255.255.0
inet6 addr: fe80::baac:6fff:fe0c:7e7e/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:50282914 errors:0 dropped:0 overruns:0 frame:0
TX packets:47054189 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:12732118873 (12.7 GB) TX bytes:34827877340 (34.8 GB)
Interrupt:21 Memory:fe9e0000-fea00000


In the last line, it says Interrupt:21.
What does this number 21 mean? I don't think it is the irq number since the /proc/interrups says differently

$ cat /proc/interrupts | grep 'CPU\|eth'

CPU0 CPU1
42: 62179752 28 PCI-MSI-edge eth0


Any answers would be appreciated.

If eth0 is working, don't worry.

I had issues in the past with a nic not working over an interrupt, and it needed 'acpi=off' on the boot line. That's not always wise today. What is the nic?

The numbers of irqs increased as PCs progressed. The IBM XT had 8 (One 8259); The AT had 16, and there it stayed for a while(Two 8259s, one fed into the other); Then we had 24 (virtual 8259s were put into some ASIC) and interrupt sharing. Boxes often assign half-assed irqs to things, and it affects old hardware. 48 seems excessive but we could be up there.