How to find the cause of the discarded packages and with error [closed]

My network is a bit slow today. Taking a look at the interfaces I saw that% w_that is the internal network there is a lot of error and discards.

ifconfig eth1
eth1      Link encap:Ethernet  Endereço de HW 00:1a:3f:79:ae:ac  
          inet end.: 192.168.20.254  Bcast:192.168.20.255  Masc:255.255.255.0
          endereço inet6: fe80::21a:3fff:fe79:aeac/64 Escopo:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Métrica:1
          pacotes RX:7488901460 erros:9555 descartados:31950 excesso:7303 quadro:0
          Pacotes TX:8342959492 erros:0 descartados:0 excesso:0 portadora:0
          colisões:0 txqueuelen:1000 
          RX bytes:2947779429718 (2.9 TB) TX bytes:6307851924629 (6.3 TB)

Running:

tcpdump -i eth1 -c200

Exit the following:

200 packets captured
30032 packets received by filter
25534 packets dropped by kernel

Is there any way to find out where these errors and discards come from?