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LACP configured ports interfere with PXE/DHCP on servers

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TitleLACP configured ports interfere with PXE/DHCP on servers
Objective
Pre-OS PXE booting is not aware of LACP/Port-channels, so it will attempt to image over 1 link at a time. 

All broadcast DHCP is fine, but DHCPACK unicast from the imaging server will have an approximately 50% (2 links) chance of returning on the correct link due to the hash algorithm that the sharing group will use on transmitting packets down 2 or more links in a group.

This causes the PXE boot process to fail and the node to reboot constantly with 100% failure every time.
Environment
EXOS All
Procedure
As of EXOS 16.2, the LACP fallback feature will allow this to work.

configure sharing <MASTER_PORT> lacp fallback enable


For more detailed information on this, see the LACP Fallback page from the EXOS User Guide.
Additional notes
On older EXOS versions, there is a workaround using Clearflow ACL:

Clearflow with the rule-count-true function to ensure the script/command is only run when the delta changes (first time no lacp packets are received and first time lacp packets are received). 

This would be a policy like that. 

Create 1 ACL for each LAG and only apply to master port. 

Policies at Policy Server: 
Policy: cnt_lacp 
entry LACP1 { 
if match all { 
ethernet-destination-address 01:80:c2:00:00:02 ; 
ethernet-type 0x8809 ; 

then { 
count LACPpkt ; 
permit ; 


entry LACP_detect { 
if match all { 
delta LACPpkt > 0 ; 
period 40 ; 

then { 


entry LACP_notdetect { 
if match all { 
delta LACPpkt == 0 ; 
period 40 ; 

then { 


entry CF_enasharing { 
if match all { 
rule-true-count LACP_detect == 1 ; 
period 40 ; 

then { 
syslog Enable_Sharing info ; 
cli "either run command here to enable sharing or do that with script that does additional checks" 


entry CF_dissharing { 
if match all { 
rule-true-count LACP_notdetect == 1 ; 
period 40 ; 

then { 
syslog Disable_Sharing info ; 
cli "either run command here to disable sharing or do that with script that does additional checks" 



Number of clients bound to policy: 1 
Client: acl bound once 

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