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Cumulus MLAG to Cisco access layer switch


Our access layer is typically a stack of 3750s that connect via port channel to a Cisco 6509 which serves as our distribution layer; all L3 gateways are on our core. We are looking at replacing the 6509 with (~6) switches running CL. We would like to connect each 3750 stack to two CL switches. Is this possible? I have worked through the CL MLAG doc, but it is not completely applicable.

In my GNS3 lab, on the 3750, the two individual ports and the port channel show up. On the CL side, the individual ports show up, but 802.3ad interface to the 3750 is down.

Is anyone aware of a sample config for the above, assuming it is even possible?
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Best answer by Tony Skalski 2 January 2019, 22:06

That was it! Thanks. Should have guessed it, because I ran into the same issue (before the holiday weekend) with a Cisco to CL LAG (one switch) and the mode balance-xor made it work. Thanks again. Taking the bootcamp training tomorrow with some co-workers. Very excited!

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Userlevel 5
In a production environment it is absolutely possible to do this. Ironically it is a bit harder to simulate. Depending on the hypervisor you're using for simulation certain packets can be gobbled up which prevents things like LACP from establishing.

Which hypervisor are you using for your GNS3 workflow?
In CL what does the cat /proc/net/bonding/* report ? (what we see here is that sometimes based on the hypervisor a bad driver will be selected which does not support a speed setting to be used by LACP in the setup).
VMware Fusion is the hypervisor. And in case it matters, in GNS3 I am using a c3725 (to represent the Cisco 3750s) and this seems not support LACP (I am using "channel-group 1 mode on").

Here is the output of 'cat /proc/net/bonding/*'. swp1-2 are the peerlink. swp3 from each CL switch links to the Cisco.

cumulus@cumulus:~$ cat /proc/net/bonding/*
Ethernet Channel Bonding Driver: v3.7.1 (April 27, 2011)

Bonding Mode: IEEE 802.3ad Dynamic link aggregation
Transmit Hash Policy: layer3+4 (1)
MII Status: up
MII Polling Interval (ms): 100
Up Delay (ms): 0
Down Delay (ms): 0

802.3ad info
LACP rate: fast
Min links: 1
Aggregator selection policy (ad_select): stable

Slave Interface: swp2
MII Status: up
Speed: 1000 Mbps
Duplex: full
Link Failure Count: 0
Permanent HW addr: 00:98:22:1b:17:02
Slave queue ID: 0
Aggregator ID: 1
Actor Churn State: none
Partner Churn State: none
Actor Churned Count: 0
Partner Churned Count: 0

Slave Interface: swp1
MII Status: up
Speed: 1000 Mbps
Duplex: full
Link Failure Count: 0
Permanent HW addr: 00:98:22:1b:17:01
Slave queue ID: 0
Aggregator ID: 1
Actor Churn State: none
Partner Churn State: none
Actor Churned Count: 0
Partner Churned Count: 0
Ethernet Channel Bonding Driver: v3.7.1 (April 27, 2011)

Bonding Mode: IEEE 802.3ad Dynamic link aggregation
Transmit Hash Policy: layer3+4 (1)
MII Status: down
MII Polling Interval (ms): 100
Up Delay (ms): 0
Down Delay (ms): 0

802.3ad info
LACP rate: fast
Min links: 1
Aggregator selection policy (ad_select): stable

Slave Interface: swp3
MII Status: up
Speed: 1000 Mbps
Duplex: full
Link Failure Count: 0
Permanent HW addr: 00:98:22:1b:17:03
Slave queue ID: 0
Aggregator ID: 1
Actor Churn State: none
Partner Churn State: churned
Actor Churned Count: 0
Partner Churned Count: 1


Thanks!!
Userlevel 5
@Tony Skalski
'and this seems not support LACP (I am using "channel-group 1 mode on").'

I would suspect this is definitely related to the issue. Cumulus uses LACP (802.3ad) by default so it won't bring the bond up until it is getting LACP PDUs from the far-side device. You can enable static mode bonding in Cumulus Linux with the `net add bond [name] bond mode balance-xor` command. This will bring the bond-up statically similar to "channel-group mode on" in Ciscoland.

Let me know how it goes!
That was it! Thanks. Should have guessed it, because I ran into the same issue (before the holiday weekend) with a Cisco to CL LAG (one switch) and the mode balance-xor made it work. Thanks again. Taking the bootcamp training tomorrow with some co-workers. Very excited!
Userlevel 5
Ahh cool, I'm just preparing the lab workbenches for your training tomorrow. Enjoy the Bootcamp, your instructor @Jason Heller is a master trainer.

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