I connected a computer with a 25G interface in Cisco Catalyst 9500-48Y4C switch. I saw ports on both PC and the switch are UP (green light). However, the switch could not learn the computer's MAC address. Also, the computer did not know the MAC address of the connected switch port. It seems to be a layer-2 problem. When I tried the ping from the computer to the switch port, as the MAC address of the switch port is not listed on the computer, the broadcast messages were sent out. But what surprised me is that switch still received the broadcast messages from the computer. What is the problem here?
-------------On the switch---------------------
show interface TwentyFiveGigE1/0/X
TwentyFiveGigE1/0/X is up, line protocol is up (connected)
Hardware is Twenty Five Gigabit Ethernet, address is 8024.8f2f.451f (bia 8024.8f2f.451f)
Internet address is 123.123.123.123/24
MTU 1500 bytes, BW 10000000 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, 10Gb/s, link type is auto, media type is SFP-10GBase-CU3M
input flow-control is on, output flow-control is off
ARP type: ARPA, ARP Timeout 04:00:00
Last input never, output 00:00:00, output hang never
Last clearing of "show interface" counters 1w2d
Input queue: 0/375/0/0 (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
3052 packets input, 201865 bytes, 0 no buffer
Received 3052 broadcasts (0 IP multicasts)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 235 multicast, 0 pause input
0 input packets with dribble condition detected
500755 packets output, 45412032 bytes, 0 underruns
Output 2 broadcasts (0 IP multicasts)
0 output errors, 0 collisions, 6 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
When I ran "ping 123.123.123.123" from the computer, the switch port updated broadcast messages:
show interface TwentyFiveGigE1/0/X
TwentyFiveGigE1/0/X is up, line protocol is up (connected)
Hardware is Twenty Five Gigabit Ethernet, address is 8024.8f2f.451f (bia 8024.8f2f.451f)
Internet address is 123.123.123.123/24
MTU 1500 bytes, BW 10000000 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, 10Gb/s, link type is auto, media type is SFP-10GBase-CU3M
input flow-control is on, output flow-control is off
ARP type: ARPA, ARP Timeout 04:00:00
Last input never, output 00:00:02, output hang never
Last clearing of "show interface" counters 1w2d
Input queue: 0/375/0/0 (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
3058 packets input, 202249 bytes, 0 no buffer
Received 3058 broadcasts (0 IP multicasts)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 235 multicast, 0 pause input
0 input packets with dribble condition detected
500773 packets output, 45415012 bytes, 0 underruns
Output 2 broadcasts (0 IP multicasts)
0 output errors, 0 collisions, 6 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
Switch did not learn MAC address at all:
show mac address-table interface TwentyFiveGigE1/0/X
Mac Address Table
-------------------------------------------
Vlan Mac Address Type Ports
---- ----------- -------- -----
Other information on the switch:
Cisco IOS XE Software, Version 17.03.04
show vlan
VLAN Name Status Ports
---- -------------------------------- --------- -------------------------------
1 default active Twe1/0/1, Twe1/0/2, Twe1/0/3
Twe1/0/4, Twe1/0/5, Twe1/0/6
Twe1/0/7, Twe1/0/8, Twe1/0/9
Twe1/0/10, Twe1/0/11, Twe1/0/12
Twe1/0/13, Twe1/0/14, Twe1/0/15
Twe1/0/16, Twe1/0/17, Twe1/0/18
Twe1/0/19, Twe1/0/20, Twe1/0/21
Twe1/0/22, Twe1/0/23, Twe1/0/24
Twe1/0/25, Twe1/0/26, Twe1/0/27
Twe1/0/28, Twe1/0/29, Twe1/0/30
Twe1/0/31, Twe1/0/32, Twe1/0/33
Twe1/0/34, Twe1/0/35, Twe1/0/36
Twe1/0/37, Twe1/0/38, Twe1/0/39
Twe1/0/40, Twe1/0/41, Twe1/0/42
Twe1/0/43, Twe1/0/44, Twe1/0/45
Twe1/0/46, Twe1/0/47, Hu1/0/50
Hu1/0/51, Hu1/0/52
2 VLAN0002 active
1002 fddi-default act/unsup
1003 token-ring-default act/unsup
1004 fddinet-default act/unsup
1005 trnet-default act/unsup
--------------On the computer--------------------------
eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 123.123.123.1 netmask 255.255.255.0 broadcast 123.123.123.255
ether 90:e2:ba:e2:76:cc txqueuelen 1000 (Ethernet)
RX packets 1894 bytes 266637 (266.6 KB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 6387 bytes 300306 (300.3 KB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
user@PC:~$ arp
Address HWtype HWaddress Flags Mask Iface
123.123.123.123 (incomplete) enp2s0f0
