unknown protocol drops (Cisco)

unknown protocol drops reporta os pacotes com protocolo desconhecido ou não configurado por interface.
Se não poder explicar esses erros, pode usar um sniffer (p.e.: wireshark) para identificar o protocolo desconhecido.

Para reproduzir uma situação com protocolo desconhecido ligamos dois routers (p.e.: 2821) costas com costas  (veja a figura).

Com uma configuração default, como abaixo, não ocorrem drops.

Router1#sh run int gi 0/1 Building configuration... Current configuration : 97 bytes ! interface GigabitEthernet0/1 ip address 99.99.99.1 255.255.255.0 duplex full speed 100 end Router2#sh run int gi 0/1 Building configuration... Current configuration : 97 bytes ! interface GigabitEthernet0/1 ip address 99.99.99.2 255.255.255.0 duplex full speed 100 end
Router1#sh int gi 0/1 GigabitEthernet0/1 is up, line protocol is up Hardware is MV96340 Ethernet, address is 001e.1323.4c11 (bia 001e.1323.4c11) Internet address is 99.99.99.1/24 MTU 1500 bytes, BW 100000 Kbit/sec, DLY 100 usec, reliability 255/255, txload 1/255, rxload 1/255 Encapsulation ARPA, loopback not set Keepalive set (10 sec) Full-duplex, 100Mb/s, media type is T output flow-control is XON, input flow-control is XON ARP type: ARPA, ARP Timeout 04:00:00 Last input 00:00:45, output 00:00:04, output hang never Last clearing of "show interface" counters 02:04:20 Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0 Queueing strategy: fifo Output queue: 0/40 (size/max) 5 minute input rate 0 bits/sec, 0 packets/sec 5 minute output rate 0 bits/sec, 0 packets/sec 125 packets input, 46064 bytes, 0 no buffer Received 124 broadcasts, 0 runts, 0 giants, 0 throttles 0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored 0 watchdog, 0 multicast, 0 pause input 0 input packets with dribble condition detected 1338 packets output, 137992 bytes, 0 underruns 0 output errors, 0 collisions, 0 interface resets 0 unknown protocol drops 0 babbles, 0 late collision, 0 deferred 0 lost carrier, 0 no carrier, 0 pause output 0 output buffer failures, 0 output buffers swapped out

Exemplo de "unknown protocol drops":
Desligando o CDP na interface Gi 0/1 do Router1 vai resultar em "unknown protocol drops" nessa interface. Os pacotes CDP deixam de ser reconhecidos e são dropados.

Router1#conf t
Enter configuration commands, one per line. End with CNTL/Z.
Router1(config)#int gigabitEthernet 0/1
Router1(config-if)#no cdp enable
Router1(config-if)#^Z
Router1#

GigabitEthernet0/1 is up, line protocol is up
Hardware is MV96340 Ethernet, address is 001e.1323.4c11 (bia 001e.1323.4c11)
Internet address is 99.99.99.1/24
MTU 1500 bytes, BW 100000 Kbit/sec, DLY 100 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Full-duplex, 100Mb/s, media type is T
output flow-control is XON, input flow-control is XON
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:28, output 00:00:01, output hang never
Last clearing of "show interface" counters 02:14:03
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
135 packets input, 49774 bytes, 0 no buffer
Received 134 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 0 multicast, 0 pause input
0 input packets with dribble condition detected
1439 packets output, 147648 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets
2 unknown protocol drops
0 babbles, 0 late collision, 0 deferred
0 lost carrier, 0 no carrier, 0 pause output
0 output buffer failures, 0 output buffers swapped out