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In an 8.0.21ag CFM environment, it appears that lower level CCM are not dropped as expected in accordance with 802.1Q 19.2.2c.

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TitleIn an 8.0.21ag CFM environment, it appears that lower level CCM are not dropped as expected in accordance with 802.1Q 19.2.2c.
Symptoms
According to 802.1Q19.2.2c, in a section of 802.1Q added by 802.1ag, one of the functions of a MEP is that it "Discards those CFM PDUs at a lower MD Level to that configured in the MEP (20.7.1)".

Unless a Brocade switch is configured for a particular level, the switch will forward all CCM for that level as plain Layer2 traffic.
Environment
  • NetIron CER Series, NetIron CES Series, NetIron MLX / MLXe Series
  • NetIronOS All Versions
Cause
It is necessary to configure a CFM level on a Brocade switch to make it recognize CCMs of that level as 802.1ag CCMs.
Resolution
To make a switch already configured as a MEP for a higher level drop CCM for a lower level, it is necessary to configure that lower level on the switch. Doing so makes the switch behave as a MIP for the lower level and drop the lower level CCM in accordance with 802.1Q 19.2.2c due to the higher level also configured.

This behavior can be observed in the following topology.

CES1 e1/1--e1/1 CES2 e1/2--e1/2 CES3 e1/1--e1/1 CES4

The full scope of 802.1Q 19.2.2c-relevant behavior can be observed in three stages.

In the first stage, CES2 and CES3 are configured as MEPs for only a higher level while CES1 and CES4 are configured as MEPs for a lower level. CES2 and CES3 blindly forward CES1 and CES4's CCMs as Layer2 frames because they are not configured as MIPs in CES1 and CES4's lower level. CES2 and CES3 maintain connectivity with each other in "show cfm connectivity". CES1 and CES4 also maintain connectivity with each other in "show cfm connectivity".

In the second stage, CES1 and CES4 are configured for as lower level MEPs while CES2 and CES3 are configured as higher level MEPs and lower level MIPs. Doing so allows CES2 and CES3 to recognize lower level CCM and discard them in accordance with 802.1Q 19.2.2c. CES2 and CES3 maintain connectivity with each other in "show cfm connectivity," but CES1 and CES4 do not because the middle two CES2 and CES3 are dropping their CCMs as expected.

In the third stage, CES1 and CES4 are configured for as higher level MEPs while CES2 and CES3 are configured as lower level MEPs and higher level MIPs. CES2 and CES3 forward CES1 and CES4's higher level CCMs as expected. CES2 and CES3 maintain connectivity with each other in "show cfm connectivity". CES1 and CES4 also maintain connectivity with each other in "show cfm connectivity".

The three stages can be configured as follows with the topology above. New configs are presented for each device only when there are changes.

STAGE1: The middle two CES2 and CES3 are configured only for level3 while the outside two are configured only for level2.

In the settings below, CES2 and CES3 maintain connectivity with each other in "show cfm connectivity". CES1 and CES4 also maintain connectivity with each other in "show cfm connectivity".

CES1:
hostname CES1
vlan 50
untagged e 1/1
cfm-enable
domain-name L2 level 2
ma-name domain2 vlan-id 50 priority 6
ccm-interval 1-second
mep 1 down port e 1/1
remote-mep 4 to 4
interface ethernet 1/1
enable


CES2:
hostname CES2
vlan 50
untagged e 1/1 to 1/2
cfm-enable
domain-name L3 level 3
ma-name domain3 vlan-id 50 priority 6
ccm-interval 1-second
mep 2 down port e 1/2
remote-mep 3 to 3
interface ethernet 1/1
enable
interface ethernet 1/2
enable


CES3:
hostname CES3
vlan 50
untagged e 1/1 to 1/2
cfm-enable
domain-name L3 level 3
ma-name domain3 vlan-id 50 priority 6
ccm-interval 1-second
mep 3 down port e 1/2
remote-mep 2 to 2
interface ethernet 1/1
enable
interface ethernet 1/2
enable


CES4:
hostname CES4
no route-only
vlan 50
untagged e 1/1
cfm-enable
domain-name L2 level 2
ma-name domain2 vlan-id 50 priority 6
ccm-interval 1-second
mep 4 down port e 1/1
remote-mep 1 to 1
interface ethernet 1/1
enable


STAGE2: The middle two CES2 and CES3 are configured as level2 MIPs by adding a level2 domain without MEP specification.

Doing so makes the middle two CES2 and CES3 drop the lower level CCM from the outside two CES1 and CES4. CES1 and CES4 lose connectivity with each other in "show cfm connectivity", as expected according to 802.1Q 19.2.2c.

CES2:
hostname CES2
vlan 50
untagged e 1/1 to 1/2
cfm-enable
domain-name L3 level 3
ma-name domain3 vlan-id 50 priority 6
ccm-interval 1-second
mep 2 down port e 1/2
remote-mep 3 to 3
domain-name L2 level 2
ma-name domain2 vlan-id 50 priority 6
interface ethernet 1/1
enable
interface ethernet 1/2
enable


CES3:
hostname CES3
vlan 50
untagged e 1/1 to 1/2
cfm-enable
domain-name L3 level 3
ma-name domain3 vlan-id 50 priority 6
ccm-interval 1-second
mep 3 down port e 1/2
remote-mep 2 to 2
domain-name L2 level 2
ma-name domain2 vlan-id 50 priority 6
interface ethernet 1/1
enable
interface ethernet 1/2
enable


STAGE3: The middle two CES2 and CES3 level3 is changed to level1.

Doing so allows the middle two to forward the higher level2 CCMs from the outside two CES1 and CES4. The outside two regain connectivity in "show cfm connectivity".

CES2:
hostname CES2
vlan 50
untagged e 1/1 to 1/2
cfm-enable
domain-name L1 level 1
ma-name domain1 vlan-id 50 priority 6
ccm-interval 1-second
mep 2 down port e 1/2
remote-mep 3 to 3
domain-name L2 level 2
ma-name domain2 vlan-id 50 priority 6
interface ethernet 1/1
enable
interface ethernet 1/2
enable


CES3:
hostname CES3
vlan 50
untagged e 1/1 to 1/2
cfm-enable
domain-name L1 level 1
ma-name domain1 vlan-id 50 priority 6
ccm-interval 1-second
mep 3 down port e 1/2
remote-mep 2 to 2
domain-name L2 level 2
ma-name domain2 vlan-id 50 priority 6
interface ethernet 1/1
enable
interface ethernet 1/2
enable
Additional notes

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