Ping fail between Cisco 4331 and ISP Router

[Techworking]

I have a Cisco 4331 router directly connected to an ISP router switch port.

Layer 2 is fine as I can see the mac address of the ISP router in the arp table.

There are no filters on the 4331 i directly connected interface

However at layer 3 pings are failing. 

Looking at the 4331 router interface i see unknown protocol drops 

sh int gi0/0/0 | i un
Last clearing of "show interface" counters 23:00:44
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
4743 packets output, 1774370 bytes, 0 underruns
41013 unknown protocol drop

sh int gi0/0/0 | i un
Last clearing of "show interface" counters 23:03:35
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
4753 packets output, 1778066 bytes, 0 underruns
41097 unknown protocol drops

I got a user to connect a laptop to the ISP router and everything worked

the ISP are typically saying the problem is on my side

I am thinking because the link to the ISP router is connected to the built in switch port they may have DTP or something enabled. I'm sure if this would cause layer 3 connectivity to fail.

Any help with this would be greatly appreciated

Thanks

[Jaderson Pessoa]

Hello,

could you share outputs below?

show interface xxx status
show interface xx switchport
show run int xx
show int xx

[Techworking]

sh int gi0/0/0 switchport

% Gi0/0/0 is not a switchable port



sh run int gi0/0/0



interface GigabitEthernet0/0/0

description

ip address x.x.x.x 255.255.255.248

no ip redirects

no ip unreachables

no ip proxy-arp

load-interval 30

media-type rj45

negotiation auto

end



#sh int gi0/0/0

GigabitEthernet0/0/0 is up, line protocol is up

Hardware is ISR4331-3x1GE, address is 50f7.22b7.5de0 (bia 50f7.22b7.5de0)

Description:

Internet address is x.x.x.x/29

MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,

reliability 255/255, txload 1/255, rxload 1/255

Encapsulation ARPA, loopback not set

Keepalive not supported

Full Duplex, 1000Mbps, link type is auto, media type is RJ45

output flow-control is off, input flow-control is off

ARP type: ARPA, ARP Timeout 04:00:00

Last input 00:00:00, output 00:00:01, output hang never

Last clearing of "show interface" counters 1d00h

Input queue: 0/375/0/0 (size/max/drops/flushes); Total output drops: 0

Queueing strategy: fifo

Output queue: 0/40 (size/max)

30 second input rate 0 bits/sec, 0 packets/sec

30 second output rate 0 bits/sec, 0 packets/sec

148788 packets input, 9025528 bytes, 0 no buffer

Received 139563 broadcasts (0 IP multicasts)

0 runts, 0 giants, 0 throttles

0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored

0 watchdog, 0 multicast, 0 pause input

5073 packets output, 1897964 bytes, 0 underruns

0 output errors, 0 collisions, 0 interface resets

43782 unknown protocol drops

0 babbles, 0 late collision, 0 deferred

1 lost carrier, 0 no carrier, 0 pause output

0 output buffer failures, 0 output buffers swapped out

[Jaderson Pessoa]

Well,

I had this same issue previously and the problem as on ISP. They cannot had configured the router properly to be a P2P, they have natted the address. If you input it directly to pc it works but in the other router doesn't work. I suggest to you go ahead with your ISP.

[marce1000]

 - Give a go with arping instead.

   M.

[Georg Pauwen]

Hello,

what are you pinging, an IP address on the same subnet as your interface (usually the default gateway) ? Do the unknown drops correspond to the amount of pings you are sending ?

[Techworking]

Hello George



Pinging default gateway

Unknown drops do not correspond with pings