Duplex Mismatch on 1921 -> 3650

[Sam Tan]

Hi SME and Engineers,

I got a duplex mismatch scenario here and need your opinion.

Scenario:

Router:

c1900-universalk9-mz.SPA.154-3.M1.bin
interface GigabitEthernet0/1
 description LAN Port
 ip address 103.224.122.49 255.255.255.248
 ip tcp adjust-mss 1452
 duplex auto
 speed 100
 no keepalive proto-up

GigabitEthernet0/1 is up, line protocol is up
  Hardware is CN Gigabit Ethernet, address is b0aa.7764.47c1 (bia b0aa.7764.47c1)
  Description: LAN Port
  Internet address is 103.224.122.49/29
  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 not set
  Full Duplex, 100Mbps, media type is RJ45
  output flow-control is unsupported, input flow-control is unsupported
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 00:00:07, output 00:00:00, output hang never
  Last clearing of "show interface" counters 1w5d
  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 207000 bits/sec, 74 packets/sec
  5 minute output rate 344000 bits/sec, 79 packets/sec
     126559062 packets input, 2781615399 bytes, 0 no buffer
     Received 35921 broadcasts (0 IP multicasts)
     0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 35008 multicast, 0 pause input
     133260637 packets output, 1942552617 bytes, 0 underruns
     0 output errors, 0 collisions, 0 interface resets
     35008 unknown protocol drops
     0 babbles, 0 late collision, 0 deferred
     0 lost carrier, 0 no carrier, 0 pause output

Switch:

Switch details:
Switch version: 03.06.04.E

interface GigabitEthernet1/0/46
description Connection Internet Line
switchport access vlan 99
speed 100
no cdp enable

GigabitEthernet1/0/46 is up, line protocol is up (connected)
  Hardware is Gigabit Ethernet, address is 74a2.e6a9.3aae (bia 74a2.e6a9.3aae)
  Description: Connection Internet Line
  MTU 1500 bytes, BW 100000 Kbit/sec, DLY 100 usec,
     reliability 255/255, txload 1/255, rxload 2/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Full-duplex, 100Mb/s, media type is 10/100/1000BaseTX
  input flow-control is off, output flow-control is unsupported
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 00:00:38, output never, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/2000/0/0 (size/max/drops/flushes); Total output drops: 3265536
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 965000 bits/sec, 104 packets/sec
  5 minute output rate 161000 bits/sec, 82 packets/sec
     3152236081 packets input, 2134901224894 bytes, 0 no buffer
     Received 1491675 broadcasts (407018 multicasts)
     0 runts, 0 giants, 0 throttles
     28337 input errors, 28337 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 407018 multicast, 0 pause input
     0 input packets with dribble condition detected
     2928757149 packets output, 1204608383637 bytes, 0 underruns
     3270906 output errors, 1802 collisions, 1 interface resets
     373476 unknown protocol drops
     0 babbles, 1458 late collision, 0 deferred
     0 lost carrier, 0 no carrier, 0 pause output
     0 output buffer failures, 0 output buffers swapped out

The weirdest thing is when the router and switch sets to Full Duplex / 100 Speed, the interface will force a half duplex on both end causing packet lost.

If set to auto duplex, only it will register correctly like the above scenario.

Any ideas? I don't see any particular bugs on these two versions.

Regards,

ST

[Mark Malone]

Hi why are the set to speed 100 when there gig ports , can you hardcode them to speed 1000 and duplex full , what happes then ? it should work

[Georg Pauwen]

Hello,

for links between Cisco devices, auto speed and auto duplex is recommended. 

I'll check for bugs...

[paul driver]

Hello

My understanding is cisco switches negotiate duplex , So if either side sets an hardcoded duplex the switch port will default to half duplex on 10/100 interfaces and full duplex on 1GB interfaces.

So when you set the duplex to auto, that why is works, and it doesn't when one side is hardcoded

res
Paul