Ethernet Segment Identifiers, ESI Types, and LACP in EVPN LAGs
This section discusses Ethernet Segment Identifiers (ESIs), ESI Types, and LACP in EVPN LAGs.
Ethernet Segment Identifiers and Numbering in EVPN LAGs
An EVPN LAG is identified using an Ethernet segment identifier (ESI). An ESI is a mandatory attribute that is required to enable EVPN LAG server multihoming.
ESI values are encoded as 10-byte integers and are used to identify a multihomed segment. The same ESI value enabled on multiple leaf switch interfaces connected to the same server or BladeCenter form an EVPN LAG. This EVPN LAG supports active-active multihoming towards the connected server.
We recommend using an ESI value that uses the same values for the first 8 bytes with changes only in the 9th and 10th bytes on a per-EVPN LAG basis. The four ESIs used later in this document follow these assigment guidelines and use the following ESI values: 00:03:03:03:03:03:03:03:03:01, 00:03:03:03:03:03:03:03:03:02, 00:03:03:03:03:03:03:03:03:03, and 00:03:03:03:03:03:03:03:03:04. Using a structured ESI assignment method simplifies network administration while also ensuring the ESI values can be used across Junos OS releases. The need to be compatible across Junos releases is required in some environments due to changes made to ES import route community handling in Junos OS Release 17.3R3.
ESI Types in EVPN LAGs
Junos OS currently supports ESI type 0 (manually hard-coded ESI value), type 1 (auto derived from LACP), and type 5 (IRB-VGA gateway ESI encoded based on autonomous system number) ESI patterns. See the EVPN Multihoming Implementation section of the EVPN Multihoming Overview document for additional information related to ESI types.
EVPN multihoming is managed at the control plane level using EVPN Type 4 routes and the ES-Import Route-Target extended community, which in Junos is an automatically derived 6-byte value taken from the 10-byte ESI value. This extended community is used within the Type-4 ES-Route to signal using EVPN BGP messages when connecting leaf devices to the same multihomed CE device.
LACP in EVPN LAGs
External devices such as servers almost always require an LACP state that matches the ESI-enabled interface on the leaf switches to ensure the server can actively send traffic across all member interfaces in the LAG bundle. Specifically, the same ESI and LACP system identifier should be configured on all links that make up a LAG bundle. To ensure the suggested system ID consistency, its a best-practice to base the system ID on the ESI you assign to each LAG.
For example, if you assign ESI 00:03:03:03:03:03:03:03:03:01 to a LAG, then it is suggested that you derive the corresponding system ID from the last 6 bytes of that ESI, i.e., “03:03:03:03:03:01”. The suggested best practice of deriving the system ID from the LAG’s ESI is demonstrated in the configurations presented later in this document.