The 3750 is configured with the following:

interface GigabitEthernet1/0/2

description CAT3524 Gi0/1

switchport trunk encapsulation dot1q

switchport mode trunk

The 3524 is configured with the following:

interface GigabitEthernet0/1

description CAT3750 Gi1/0/2

switchport trunk encapsulation dot1q

switchport mode trunk

The 3750 is showing connected and the 3524 is showing not connected.

There is no information about trunked vlans.

Moreover all trunked vlans should be added to vlandatabase.

BR. Amdil

Right and I have them added.

The trunk is defaulted to allow 1-1005 vlans which are included in the vlan database.

Since switchport trunk allowed 1-1005 is default it will not show up in the configuration.

You didn't mention about vlan's no. so I asked.

Please, let me know the output from the following commands:

cat3750 & cat3524

sh int Gi1/0/2 ; sh int gi0/1

sh int tru

BR.Amdil

cat3750#sh int Gi1/0/2

GigabitEthernet1/0/2 is up, line protocol is up (connected)

Hardware is Gigabit Ethernet, address is 0014.6a1e.5402 (bia 0014.6a1e.5402)

Description: CAT3524 Gi0/1

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

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

Encapsulation ARPA, loopback not set

Keepalive not set

Full-duplex, 1000Mb/s, link type is auto, media type is 10/100/1000BaseTX SFP

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

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

Last input 00:11:25, output 00:00:00, 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 0 bits/sec, 0 packets/sec

5 minute output rate 3000 bits/sec, 5 packets/sec

1071 packets input, 86556 bytes, 0 no buffer

Received 1017 broadcasts (0 multicast)

0 runts, 0 giants, 0 throttles

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

0 watchdog, 1006 multicast, 0 pause input

0 input packets with dribble condition detected

6131 packets output, 567933 bytes, 0 underruns

0 output errors, 0 collisions, 1 interface resets

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

CAT3524#sh int gi0/1

GigabitEthernet0/1 is down, line protocol is down

Hardware is Gigabit Ethernet, address is 0007.50a6.f919 (bia 0007.50a6.f919)

Description: CAT3750 Gi1/0/2

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

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

Encapsulation ARPA, loopback not set

Keepalive not set

Full-duplex, 1000Mb/s, media type is T

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

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

Last input 2d05h, output 00:11:58, output hang never

Last clearing of "show interface" counters never

Queueing strategy: fifo

Output queue 0/40, 0 drops; input queue 0/75, 0 drops

5 minute input rate 0 bits/sec, 0 packets/sec

5 minute output rate 0 bits/sec, 0 packets/sec

75 packets input, 842488 bytes, 0 no buffer

Received 64 broadcasts, 0 runts, 0 giants, 0 throttles

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

0 watchdog, 12 multicast, 0 pause input

73 packets output, 8703 bytes, 0 underruns

0 output errors, 0 collisions, 26 interface resets

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

cat3750#sh int tru

Port Mode Encapsulation Status Native vlan

Fa1/0/10 on 802.1q trunking 10

Fa1/0/11 on 802.1q trunking 10

Gi1/0/2 on 802.1q trunking 1

Port Vlans allowed on trunk

Fa1/0/10 1-4094

Fa1/0/11 1-4094

Gi1/0/2 1-4094

Port Vlans allowed and active in management domain

Fa1/0/10 1-3,5,7,10,100,192,210

Fa1/0/11 1-3,5,7,10,100,192,210

Gi1/0/2 1-3,5,7,10,100,192,210

Port Vlans in spanning tree forwarding state and not pruned

Fa1/0/10 1-3,5,7,10,100,192,210

Fa1/0/11 1-3,5,7,10,100,192,210

Gi1/0/2 1-3,5,7,10,100,192,210

The trunk configuration is OK.

You have a problem with physical connection.

("GigabitEthernet0/1 is down, line protocol is down")

Check your GBIC and particularly cable.

BR.Amdil