Network gets disconnected every few minutes (Cisco router c921-4p).

[klukasik]

Hello, 

I build simple network using Cisco Devices (Router C921-4P and 2x Switch SG220-26).

First of all I configure my Router just to have connection on WAN and LAN ports. I connect ISP to the WAN port (gigabitethernet 5) then I connected to the GigabitEthernet 0 one Switch and to the GigabitEthernet 1 second one (both GigabitEthernet 0 and GigabitEthernet 1 are LAN ports). I don't configure that switches at all (only on Cisco Switch web interface I setup for them static ip, first one gets 192.168.2.100, second one 192.168.2.101).

There is connection I see all devices connected to this network (also devices has internet connection) but every few minutes each device gets disconnected. That disconnection takes few minutes where each one has "undefined network" and then connection back. When devices are disconnected I see devices that are connected to the same switch with me but for example there is no connection with Router. 

Am I missing something? I just want on all switch ports have same network with stable connection. HELP


Show run on router looks like:

Building configuration...

Current configuration : 1665 bytes
!
! Last configuration change at 08:47:02 UTC Fri Sep 23 2022 by movitech
!
version 15.8
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname my-name
!
boot-start-marker
boot-end-marker
!
!
enable secret 5 $1$t93s$/V2omb4pVoYEPXBaeMhiS.
!
no aaa new-model
memory-size iomem 25
!
!
!
!
!
!
!
!
ip dhcp excluded-address 192.168.2.1
!
ip dhcp pool LAN
network 192.168.2.0 255.255.255.0
default-router 192.168.2.1
dns-server 8.8.8.8
!
!
!
ip domain name my-name.pl

ip cef
no ipv6 cef
multilink bundle-name authenticated
!
!
!
license udi pid C921-4P sn PSZ25461HC2
!
!
username movitech privilege 15 secret 5 $1$dMoR$0jB6zN4skcvJ8DR3Yn9Tq.
!
redundancy
!
!
!
!
!
!
interface GigabitEthernet0
description SWITCH GORA
no ip address
!
interface GigabitEthernet1
description SWITCH DOL
no ip address
!
interface GigabitEthernet2
no ip address
!
interface GigabitEthernet3
no ip address
!
interface GigabitEthernet4
no ip address
shutdown
duplex auto
speed auto
!
interface GigabitEthernet5
description WAN Interface
ip address dhcp
ip nat outside
ip virtual-reassembly in
duplex auto
speed auto
!
interface Vlan1
description LAN interface
ip address 192.168.2.1 255.255.255.0
ip nat inside
ip virtual-reassembly in
!
ip forward-protocol nd
no ip http server
no ip http secure-server
!
!
ip nat inside source list 1 interface GigabitEthernet5 overload
ip route 0.0.0.0 0.0.0.0 GigabitEthernet5 dhcp
ip ssh version 2
!
!
!
access-list 1 permit 192.168.2.0 0.0.0.255
!
control-plane
!
!
line con 0
line vty 0 4
login local
transport input ssh
!
scheduler allocate 20000 1000
!
end

[balaji.bandi]

is this disconnection issue, the device connected to switches ?

how about from router are you able to ping 8.8.8.8 when you lost connection from clients. how about from switch are you able to ping ?

Looks like you need to configure the switch - remove smart port configuration on your SMB switches.

can you post show interface gig 0

[klukasik]

is this disconnection issue, the device connected to switches ?

Yea device is connected to the switch. Like I said before when it's disconnected I see all devices connected to the specific switch but there is no connection to the Router. I will try ping 8.8.8.8 while I will be connected directly to the router while other devices gets disconnected. But there is no internet on clients. 


hers show interface gig 0

GigabitEthernet0 is up, line protocol is up
Hardware is Gigabit Ethernet, address is a49b.cd85.f314 (bia a49b.cd85.f314)
Description: SWITCH GORA
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 set (10 sec)
Full-duplex, 1000Mb/s
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:20, output never, output hang never
Last clearing of "show interface" counters never
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 104000 bits/sec, 26 packets/sec
5 minute output rate 377000 bits/sec, 44 packets/sec
7771587 packets input, 4900817824 bytes, 0 no buffer
Received 62525 broadcasts (51670 multicasts)
0 runts, 0 giants, 0 throttles
19 input errors, 0 CRC, 0 frame, 19 overrun, 0 ignored
0 watchdog, 0 multicast, 0 pause input
0 input packets with dribble condition detected
12146938 packets output, 14020281155 bytes, 0 underruns
0 output errors, 0 collisions, 2 interface resets
737 unknown protocol drops
0 babbles, 0 late collision, 0 deferred
7 lost carrier, 0 no carrier, 0 pause output
0 output buffer failures, 0 output buffers swapped out

here gig 1

GigabitEthernet1 is up, line protocol is up
Hardware is Gigabit Ethernet, address is a49b.cd85.f315 (bia a49b.cd85.f315)
Description: SWITCH DOL
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 set (10 sec)
Full-duplex, 1000Mb/s
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:01, output never, output hang never
Last clearing of "show interface" counters never
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 3000 bits/sec, 2 packets/sec
5 minute output rate 61000 bits/sec, 5 packets/sec
11010890 packets input, 13180719777 bytes, 0 no buffer
Received 48940 broadcasts (17857 multicasts)
0 runts, 0 giants, 0 throttles
16 input errors, 0 CRC, 0 frame, 16 overrun, 0 ignored
0 watchdog, 0 multicast, 0 pause input
0 input packets with dribble condition detected
15847699 packets output, 20058665385 bytes, 0 underruns
0 output errors, 0 collisions, 2 interface resets
638 unknown protocol drops
0 babbles, 0 late collision, 0 deferred
3 lost carrier, 0 no carrier, 0 pause output
0 output buffer failures, 0 output buffers swapped out

---

[balaji.bandi]

737 unknown protocol drops

638 unknown protocol drops

when the user lots connection, is the interface show up on the switch side connected port ?

[klukasik]

To check that information (show interface gig 0) I need to have connection to router. When cliencts get disconnected there is no connection to the router (I mean ssh connection). I can connect to the router directly and then check what are on the ports (but this could be not reliable). 

[MHM Cisco World]

https://www.cisco.com/c/en/us/support/docs/dial-access/asynchronous-connections/15286-serial-overruns.html#:~:text=Overruns%20appear%20in%20the%20output,a%20limitation%20of%20the%20hardware.

You have overrun ?

This can something with buffer 

[klukasik]

To be honest I don't know. If there is overrun configuration it's default one because I don't configure with it

[Georg Pauwen]

Hello,

I think the SG220 switches might have their own internal DHCP server turned on as well (they dish out the same 192.168.2.0/24 address space that you have configured on the router). You might want to turn the DHCP servers on the switches off...

[klukasik]

There is no DHCP options on this switch. 

There is no DHCP options on this switch. On this photos you see only options that I have there. 

[klukasik]

@Georg Pauwen @MHM Cisco World @balaji.bandi  

I noticed strange thing. When new clienct connects to the network then everyone gets disconnected. 

Anyway when clients gets disconnected I go and connect directly to the router and check interfaces. 

This is how looks switch interface:

GigabitEthernet1 is up, line protocol is up
Hardware is Gigabit Ethernet, address is a49b.cd85.f315 (bia a49b.cd85.f315)
Description: SWITCH DOWN
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 set (10 sec)
Full-duplex, 1000Mb/s
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:01, output never, output hang never
Last clearing of "show interface" counters never
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 420000 bits/sec, 47 packets/sec
5 minute output rate 385000 bits/sec, 49 packets/sec
11588399 packets input, 13303521863 bytes, 0 no buffer
Received 229776 broadcasts (151066 multicasts)
0 runts, 0 giants, 0 throttles
215 input errors, 0 CRC, 0 frame, 215 overrun, 0 ignored
0 watchdog, 0 multicast, 0 pause input
0 input packets with dribble condition detected
16335642 packets output, 20258803193 bytes, 0 underruns
0 output errors, 0 collisions, 2 interface resets
8392 unknown protocol drops
0 babbles, 0 late collision, 0 deferred
3 lost carrier, 0 no carrier, 0 pause output
0 output buffer failures, 0 output buffers swapped out


And like this looks my connection directly to the router.

GigabitEthernet3 is up, line protocol is up
Hardware is Gigabit Ethernet, address is a49b.cd85.f317 (bia a49b.cd85.f317)
MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set

On switch side there is a lot of input errors and even more unknow protocol drops. When I directly connect there was no problem and everything works great. So there is problem with switches. But what problem exactly I don't know. 
Keepalive set (10 sec)
Full-duplex, 1000Mb/s
ARP type: ARPA, ARP Timeout 04:00:00
Last input never, output never, output hang never
Last clearing of "show interface" counters never
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 3000 bits/sec, 3 packets/sec
5 minute output rate 16000 bits/sec, 7 packets/sec
9050 packets input, 3056585 bytes, 0 no buffer
Received 1882 broadcasts (6187 multicasts)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 0 multicast, 1764 pause input
0 input packets with dribble condition detected
27634 packets output, 4416850 bytes, 0 underruns
0 output errors, 0 collisions, 2 interface resets
0 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

[klukasik]

@Georg Pauwen @MHM Cisco World @balaji.bandi 

I noticed one more thing, when I turn off one of the switches, clients connected to the other one have normal stable connection without disconecting. So there is a problem that this 2 switches conflict each other. What can cause this?

[Georg Pauwen]

Hello,

since you do not have any redundant paths, try and turn off STP on both switches altogether...

[klukasik]

One of the switches has automatic DHCP (didn't noticed it ealier because second one doesn't have this option and this are the same devices) so i disabled it, then I disable STP and change switch ports from trunk to general and now it's working. Thanks for help everyone. 

[Georg Pauwen]

Good stuff. Keep monitoring...