is odd number of links in lag group ok
I have (2) 10 gig links bundled in a lag to my upstream internet provider. and we need more internet capacity. Is it cool to add a third 10 gig to my existing 20 gig lag internet connection? I'm asking since I heard in the past something negative about odd numbers of lag members. .but I also have heard that it's not a big deal. Let me know please -Aaron
On May 15, 2018, at 11:15 AM, Aaron Gould <aaron1@gvtc.com> wrote:
I have (2) 10 gig links bundled in a lag to my upstream internet provider. and we need more internet capacity. Is it cool to add a third 10 gig to my existing 20 gig lag internet connection?
I'm asking since I heard in the past something negative about odd numbers of lag members. .but I also have heard that it's not a big deal. Let me know please
Much of this depends on the hardware, software and what hashing is used inbound outbound traffic directions, etc. It will likely work the way you expect, but one may be warmer than the other if traffic ends up overloading a single bucket in the hash. - Jared
On 15/May/18 17:20, Jared Mauch wrote:
Much of this depends on the hardware, software and what hashing is used inbound outbound traffic directions, etc.
It will likely work the way you expect, but one may be warmer than the other if traffic ends up overloading a single bucket in the hash.
We haven't had a major issue when loading traffic over even or odd links. If you have decent hardware and software, it should all be fine, particularly if your traffic is all or mostly IP. If you've got non-IP traffic in there, and your box cannot look into the payload to determine entropy, then things could get interesting. But this will happen even when you have even links... it's not anything specific to how many member links you have in the LAG, but rather, the router's need to maintain per-flow load balancing with limited information beyond Layer 2 data. That said, an even number of links just leaves the warm & fuzzies turned on :-)... Mark.
On 15/05/18 16:28, Mark Tinka wrote:
That said, an even number of links just leaves the warm & fuzzies turned on :-)...
Well, power of two, surely? 6 is even, but is not a "good" number of links for a lag group. (Extreme X8 supports up to 64 links in a group, and Enterasys up to 127 if I recall correctly. Though Enterasys, unusually, seems to support round-robin load balancing in which case the argument for powers of 2 numbers of links ceases to make sense.)
This is implementation specific. Consider hash result returning range 0-15. Then number of port count as divisor of 16/n must result in an integer value. To workaround this issue, you either have larger range of hash results, in which case unequal distribution has small bias, or you have different hash functions depending on port count so that that hash returns appropriate range for given port count. Certainly solvable problem, and generally non-issue. On 15 May 2018 at 21:46, Adam Atkinson <ghira@mistral.co.uk> wrote:
On 15/05/18 16:28, Mark Tinka wrote:
That said, an even number of links just leaves the warm & fuzzies turned on :-)...
Well, power of two, surely? 6 is even, but is not a "good" number of links for a lag group.
(Extreme X8 supports up to 64 links in a group, and Enterasys up to 127 if I recall correctly. Though Enterasys, unusually, seems to support round-robin load balancing in which case the argument for powers of 2 numbers of links ceases to make sense.)
-- ++ytti
It will work fine if you have a good modern router. Consider this; all evenly grouped LAGs are odd in their failed conditions. -Ben
On May 15, 2018, at 8:28 AM, Mark Tinka <mark.tinka@seacom.mu> wrote:
On 15/May/18 17:20, Jared Mauch wrote:
Much of this depends on the hardware, software and what hashing is used inbound outbound traffic directions, etc.
It will likely work the way you expect, but one may be warmer than the other if traffic ends up overloading a single bucket in the hash.
We haven't had a major issue when loading traffic over even or odd links. If you have decent hardware and software, it should all be fine, particularly if your traffic is all or mostly IP.
If you've got non-IP traffic in there, and your box cannot look into the payload to determine entropy, then things could get interesting. But this will happen even when you have even links... it's not anything specific to how many member links you have in the LAG, but rather, the router's need to maintain per-flow load balancing with limited information beyond Layer 2 data.
That said, an even number of links just leaves the warm & fuzzies turned on :-)...
Mark.
As others have noted, there can be implementation specific issues that you can't necessarily predict but most typically when I hear "odd vs even" discussions, usually the caveat is not a trunk but a redundant connection. Putting three links on router A and two links on router B obviously doesn't work well. On Tue, May 15, 2018 at 10:15:19AM -0500, Aaron Gould wrote:
I have (2) 10 gig links bundled in a lag to my upstream internet provider. and we need more internet capacity. Is it cool to add a third 10 gig to my existing 20 gig lag internet connection?
I'm asking since I heard in the past something negative about odd numbers of lag members. .but I also have heard that it's not a big deal. Let me know please
-Aaron
--- Wayne Bouchard web@typo.org Network Dude http://www.typo.org/~web/
While it goes without saying that you need the same (can be 5!) number of links to each router in a multichassis LAG, what isn’t so obvious are things like port groups etc. If you have an oversubscribed platform, you might need to look at running each wire in a LAG to different port groups, and then look at things like switch ASICs and span those as well. Even try to span diverse slots/modules if you can. But 5 6 or 4 per chassis shouldn’t make a huge difference. -Ben
On May 16, 2018, at 3:48 PM, Wayne Bouchard <web@typo.org> wrote:
As others have noted, there can be implementation specific issues that you can't necessarily predict but most typically when I hear "odd vs even" discussions, usually the caveat is not a trunk but a redundant connection. Putting three links on router A and two links on router B obviously doesn't work well.
On Tue, May 15, 2018 at 10:15:19AM -0500, Aaron Gould wrote: I have (2) 10 gig links bundled in a lag to my upstream internet provider. and we need more internet capacity. Is it cool to add a third 10 gig to my existing 20 gig lag internet connection?
I'm asking since I heard in the past something negative about odd numbers of lag members. .but I also have heard that it's not a big deal. Let me know please
-Aaron
--- Wayne Bouchard web@typo.org Network Dude http://www.typo.org/~web/
On 17/May/18 01:32, Ben Cannon wrote:
While it goes without saying that you need the same (can be 5!) number of links to each router in a multichassis LAG, what isn’t so obvious are things like port groups etc.
I'm not sure the OP was talking about MC-LAG. Just a regular LAG. Mark.
participants (7)
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Aaron Gould -
Adam Atkinson -
Ben Cannon -
Jared Mauch -
Mark Tinka -
Saku Ytti -
Wayne Bouchard