Solved: LACP link failure

akhoonwaseem · ‎04-15-2022

Hi Need your help to understand for LACP I start continuous ping between PC0 and PC1 over etherchannel. When I shut one interface fa0/2 there is no ping drop but when I bring the interface back up I observer ping drop

Can you please explain me what is the reason for it and is it normal behavior of LACP as it is a Link aggregation and not a real HA solution. As once link comes back up it starts running algorithms again so etherchannel recalculates which ethernet to select for traffic flow

David Ruess · ‎04-15-2022

Hello,

Hopefully this helps some.

A couple things I noticed.

1.) Your port channel was in access mode. I would change that to trunk mode as they are connected to another switch and not an end device. I don't think its required but if you want more than 1 VLAN across it at some point, it will fix that.

2.) I created an Interface VLAN 1 and put an IP address on each switch 192.168.10.3\192.168.10.4 255.255.255.0 respectively. This allowed me to do a continuous ping of 1000 packets to test

3.) When I shut down an interface and brought it back up it took a long time to come up and dropped pings as you said. My BEST guess for this happening is its still going through its initial spanning-tree states before actually sending traffic. So while it could show as UP in the port channel it may not be sending traffic until this process completes. I lost several packets while this was going on.

4.) I added this command to both port-channels 'spanning-tree portfast trunk' (this basically brings up the interface right away bypassing spanning-tree timers). This allowed me to achieve 100% continuous ping.

Hope that helps out a bit.

-David

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balaji.bandi · ‎04-15-2022

check what Load-balance method right now :

here is the load-balance method and how it works :

https://www.cisco.com/c/en/us/support/docs/lan-switching/etherchannel/12023-4.html#cat2950_3550

show etherchannel load-balance.

if this L2 switches I use this and test it - load-balancing to src-dst-mixed-ip-port

below works (most of the Physical hardware, never tested on virtual last time I tested never worked )

test etherchannel load-balance interface port-channel number {ip | mac} [source_ip_add |

test etherchannel load-balance interface port-channel 1 IP PC1 PC2 ( replace PC1 and PC2 with IP)

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akhoonwaseem · ‎04-15-2022

Thank you Balaji,

I am testing on L2 switches on packet tracer. Now I configured PO as access and assigned to VLAN. Then assigned IP to SVIs and tested the ether-channel. The only issue here is I am not able to run a continuous ping from switch to observe if there is any packet loss when I shut and unshut one of the interfaces.

balaji.bandi · ‎04-15-2022

post the output :

show etherchannel load-balance.

also suggest some documents, when you chance to read and understand the load-balance how it works.

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balaji.bandi · ‎04-16-2022

here is my test Lab that works as expected.

FES1 and 2 config :

interface Port-channel1
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
!
interface Ethernet0/1
switchport trunk encapsulation dot1q
switchport mode trunk
duplex full
no shut
channel-group 1 mode active
!
!
interface Ethernet0/3
switchport trunk encapsulation dot1q
switchport mode trunk
duplex full
no shut
channel-group 1 mode active
!
interface Port-channel1
no shut
!
end

PC1 and PC2 10.10.10.1 and 10.10.10.2

FES1#show etherchannel load-balance
EtherChannel Load-Balancing Configuration:
src-dst-ip

no issue found - all work as expected

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akhoonwaseem · ‎04-16-2022

Hi Balaji,

Please let me know which simulator is that. Can you please share this lab in zip.

Thank you for your help

balaji.bandi · ‎04-17-2022

i am not a PT user, this is PNET

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MHM Cisco World · ‎04-15-2022

what is mode you use for LACP ? is it ON/ON ?
if yes then change it to be active/active

and test again

akhoonwaseem · ‎04-15-2022

It is active active

MHM Cisco World · ‎04-15-2022

can I see config for one SW ? share here as text

akhoonwaseem · ‎04-16-2022

Switch#show running-config

Building configuration...

Current configuration : 1236 bytes

!

version 15.0

no service timestamps log datetime msec

no service timestamps debug datetime msec

no service password-encryption

!

hostname Switch

!

spanning-tree mode pvst

spanning-tree extend system-id

!

interface Port-channel1

switchport mode access

!

interface FastEthernet0/1

switchport mode access

channel-group 1 mode active

!

interface FastEthernet0/2

switchport mode access

channel-group 1 mode active

!

interface FastEthernet0/3

!

interface FastEthernet0/4

!

interface FastEthernet0/5

!

interface FastEthernet0/6

!

interface FastEthernet0/7

!

interface GigabitEthernet0/1

!

interface GigabitEthernet0/2

!

interface Vlan1

no ip address

shutdown

line con 0

!

line vty 0 4

login

line vty 5 15

login

!

end

MHM Cisco World · ‎04-16-2022

Not sure 100% but let see If I am right
remove
spanning-tree mode past
let SW run RSTP instead.
do the test again. show result.

akhoonwaseem · ‎04-18-2022

Thank you,

By changing STP to RSTP there was better convergence time however still few packet drops were observed.

Issue got resolved by enabling spanning tree postfast trunk on portchannel interface.

interface Port-channel1

switchport mode trunk

spanning-tree portfast trunk

Br

Georg Pauwen · ‎04-15-2022

Hello,

if this is a Packet Tracer 'problem' keep in mind that this is a simulator that might not behave like 'real' switches. Can you post the zipped project (.pkt) file ?

akhoonwaseem · ‎04-15-2022

Hi Gerog,

Please find attached project file.

Thank you