2960-x Stack - Second SFP touch to Core?

[lostsurfer24]

I have a 2960-X stack with 4 switches in a stack configuration. I have one touch via SFP (te1/0/1) to my core and was wondering if i could setup a second touch to my core switch from the last switch in the stack te4/0/1 for redundancy? If so how would I configure the SFP on te4/0/1 so as to not create a loop?

[Reza Sharifi · Accepted solution]

The best way to do this is to put both interfaces (1/0/1 and 4/0/1) into a Portchannel.  This way you have link redundancy and no need to worry about any loops as both interfaces logically look like one.  You can use LACP, PAGP, or mode on.

Here is the config guide:

https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst2960x/software/15-0_2_EX/layer2/configuration_guide/b_lay2_152ex_2960-x_cg/b_lay2_152ex_2960-x_cg_chapter_010.html

HTH

[lostsurfer24]

Thank you for your quick response, seem to still have issues. Seeing a loop with the config:

interface TenGigabitEthernet1/0/1
switchport mode trunk
channel-group 2 mode active

interface TenGigabitEthernet4/0/1
switchport mode trunk
channel-group 2 mode active

I've verified that I configured the port groups properly on both sides, any suggestions? 

[Joseph W. Doherty]

Your stack is a "true" stack, i.e. you're using stack modules?

What's the core device?

[lostsurfer24]

yes, I'm using 4 2960x switches with stack modules. 

My core device is a 3850 in a stack configuration. 

[Joseph W. Doherty]

What does Etherchannel summary show on both sides?

[lostsurfer24]

When the etherchannel is up, any devices connected to any switches in the 2960 stack can't get out to the internet and cdp nei shows 2 entries to the 3850.

2960------

2960_Stack_2#sho int po1
Port-channel1 is up, line protocol is up (connected)
Hardware is EtherChannel, address is 
Description: 3850
MTU 1500 bytes, BW 20000000 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 unknown
input flow-control is off, output flow-control is unsupported
Members in this channel: Te1/0/1 Te4/0/1
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:00, output 01:06:11, 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 202000 bits/sec, 65 packets/sec
5 minute output rate 120000 bits/sec, 29 packets/sec
2867288 packets input, 1177174158 bytes, 0 no buffer
Received 2045587 broadcasts (1884640 multicasts)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 1884640 multicast, 0 pause input
0 input packets with dribble condition detected
1267577 packets output, 518523245 bytes, 0 underruns
0 output errors, 0 collisions, 4 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

3850-----

3850_Core#sho int po10
Port-channel10 is up, line protocol is up (connected)
Hardware is EtherChannel, address is 
Description: 2960_Stack_2
MTU 1500 bytes, BW 20000000 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
input flow-control is off, output flow-control is unsupported
Members in this channel: Te1/1/2 Te2/1/2
ARP type: ARPA, ARP Timeout 04:00:00
Last input 01:04:22, 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: 0
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 93000 bits/sec, 24 packets/sec
5 minute output rate 147000 bits/sec, 54 packets/sec
1885869 packets input, 717739834 bytes, 0 no buffer
Received 192428 broadcasts (87338 multicasts)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 87338 multicast, 0 pause input
0 input packets with dribble condition detected
21774219 packets output, 5895275426 bytes, 0 underruns
0 output errors, 0 collisions, 2 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

[Joseph W. Doherty]

Port-channel will show up with one link.

Again, could show etherchannel summary from both devices?

[lostsurfer24]

Could you please tell me how to do so?

[Joseph W. Doherty]

show etherchannel summary

[lostsurfer24]

2960_Stack_2#sho etherchannel summary
Flags: D - down P - bundled in port-channel
I - stand-alone s - suspended
H - Hot-standby (LACP only)
R - Layer3 S - Layer2
U - in use f - failed to allocate aggregator

M - not in use, minimum links not met
u - unsuitable for bundling
w - waiting to be aggregated
d - default port

Number of channel-groups in use: 5
Number of aggregators: 5

Group Port-channel Protocol Ports
------+-------------+-----------+-----------------------------------------------
1 Po1(SU) LACP Te1/0/1(P) Te4/0/1(P)
3 Po3(SU) LACP Gi1/0/47(P) Gi1/0/48(P)
4 Po4(SU) LACP Gi2/0/47(P) Gi2/0/48(P)
5 Po5(SU) LACP Gi3/0/47(P) Gi3/0/48(P)
6 Po6(SU) LACP Gi4/0/47(P) Gi4/0/48(P)