Re: [bess] A question on using EVPN label and Alias label in load balancing

[Jide Akintola <[e-mail]>]

Hi Jaikumar,
As per the rfc, aliasing is define as the ability of a PE to signal that it has reachability to an EVPN instance on a given ES even when it has learned no MAC addresses from that EVI/ES. It is advertised with Ethernet A-D per EVI type 1 routes.

Aliasing improves load-balancing by allowing remote VNEs to continue to load-balance traffic evenly though they have only received a single MAC/IP from a single ingress VNE. Meaning a remote PE that receives a MAC/IP Advertisement route (type 2 route) with a non-reserved ESI would consider the advertised MAC address to be reachable via all PEs that have advertised reachability to that MAC address EVI/ES via the Ethernet A-D per EVI route.

In your example, it would mean that if MAC1 is only learned by PE3 from PE1, but because PE3 has received Ethernet A-D per EVI type 1 route with aliasing label from PE2, it would consider that MAC1 is also reacheable via PE2 and would load balance traffic destined for MAC1 to both PE1 and PE2.

For cases where the MAC1 is learnt from PE1 and PE2 by PE3, then aliasing should not come into play.

There are some optimization done by some vendor using proxy advertisement via PE2 to mitigate traffic loss for cases where say PE3 only learns MAC1 from say PE1 and say you lost PE1.

Many thanks. 
 
Cheers, 
 
Jide 

    On Monday, 18 February 2019, 10:08:02 GMT, Jaikumar Somasundaram <[e-mail]> wrote:  
 
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Hi All,
 
                     --------------
 
                     |            |
 
              PORT1 |  DEVICE1   |PORT3
 
       --------------|     PE1    |-------------
 
       |      1/5    |  2.2.2.2   | 1/4         |
 
       |             |            |             |
 
       |             --------------             |
 
       |PORT1              |PORT2               |PORT2
 
--------------            |             +------------+            --------------     
 
 |            |            |             |            |            |            |    
 
 | DEVICE4    |            |             |            |PORT1       | DEVICE4    |
 
 | (CE1)      |            |             |   DEVICE3  |------------| (CE2)      |
 
 | Multi-home |            |             |     PE3     |       PORT3| Single home|
 
 |            |            |             |   4.4.4.4  |            |            |
 
--------------            |             +------------+            --------------      
 
       |PORT2              |1/1                |PORT3
 
       |                   |PORT2              | 1/6
 
       |             --------------            |
 
       |             |            |            |
 
       |       PORT1 |  DEVICE2   |            |
 
       --------------|    PE2     |-------------
 
                1/4  |  3.3.3.3   |PORT3
 
                     |            |1/4
 
                     --------------
 
  
 
Let’s say CE1 is connected to PE1 and PE2 (all-active case)
 
and PE1 and PE2 learn same MAC1 entry (say different destination)
 
PE3 will learn MAC1 from both PE1 and PE2 with their respective
 
EVPN label (Assume BGP ECMP is enabled). As part of load balancing,
 
should PE3 always use EVPN label to send the frame destined to MAC1
 
or can Alias label also be used? what is the need of using EVPN label?
 
  
 
Thanks & Regards
 
Jaikumar S
 
  
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