Answer by Daniele Santi for Squid or Kernel buffer overflow

A fast search on google for: ping no buffer space available returns various forum thread which seems to agree on this point:

The two NICs share the same IRQ or maybe one of them shares it with another card/ide/usb device.

You could try a cat /proc/interrupts and see if that's the case.

For example on a server with two NICs I have:

0:      105539   IO-APIC-edge      timer1:           2   IO-APIC-edge      i80422:           0   XT-PIC-XT         cascade8:           1   IO-APIC-edge      rtc010:          0   IO-APIC-fasteoi   ohci_hcd:usb112:          4   IO-APIC-edge      i804214:  882208736   IO-APIC-edge      ide015:          0   IO-APIC-edge      ide122: 3552346607   IO-APIC-fasteoi   eth023: 3776214353   IO-APIC-fasteoi   eth1

so no sharing here.