Hi Jeffrey,
I think the confusion is between the terms Bridge Domain (BD) and Bridge Table
(BT). Bridge Domain is equivalent to a VLAN which in turn can be represented
by multiple VIDs. A bridge table is basically a MAC table. You can have
multiple VLANs (and thus BDs) mapped to the same MAC table (just like IEEE SVL
mode). However, if you map multiple VLANs in the same MAC table, then it is
assumed that MACs are unique across those VLANs (which is a big assumption) but
is supported nonetheless in both IEEE 802.1Q and EVPN.
To remove the confusion and ambiguity, I will change the text in RFC7432bis
from:
“ * In VLAN-bundle mode, which can be considered as analogous to SVL
mode in 802.1Q, there is one BD per EVI and one BT per MAC-VRF
with multiple VIDs representing that BD.”
To:
“ * In VLAN-bundle mode, which can be considered as analogous to SVL
mode in 802.1Q, there is one BT per MAC-VRF
with multiple BDs (i.e., VLANs) mapping to the same BT.”
Regarding “mode” versus “model” for service interfaces, I am OK with changing
them to “model”.
Cheers,
Ali
From: Jeffrey (Zhaohui) Zhang
Date: Wednesday, May 28, 2025 at 7:45 AM
To: 'BESS'
Subject: [bess] Re: How many BDs in a vlan bundle EVI?
This question actually started with the following in RFC9136:
BD: Broadcast Domain. As per [RFC7432], an EVI consists of a
single BD or multiple BDs. In case of VLAN-bundle and
VLAN-based service models (see [RFC7432]), a BD is
equivalent to an EVI. In case of a VLAN-aware bundle
service model, an EVI contains multiple BDs. Also, in this
document, "BD" and "subnet" are equivalent terms.
It says that in the case of vlan-bundle model, a BD is equivalent to an EVI,
contradicting to RFC7432.
BTW, in my shepherd review of rfc7432bis, I pointed out that I always struggle
with the term "service interface" (vlan-based, vlan-bundle, vlan-aware, etc.)
and suggested to use "service model/mode". While writing this email, I noticed
that RFC9136 already uses "service models" and rfc7432bis also uses term "mode"
in section 6.4. I think we should standardize to "model".
Jeffrey
Juniper Business Use Only
-Original Message-
From: Jeffrey (Zhaohui) Zhang
Sent: Wednesday, May 28, 2025 10:38 AM
To: 'BESS'
Subject: How many BDs in a vlan bundle EVI?
Hi,
RFC7432 says a vlan bundle EVI has multiple BDs:
6.2. VLAN Bundle Service Interface
With this service interface, an EVPN instance corresponds to multiple
broadcast domains (e.g., multiple VLANs);
RFC7432bis says the same in 6.2, but then says in 6.4 that it only has one BD:
* In VLAN-bundle mode, which can be considered as analogous to SVL
mode in 802.1Q, there is one BD per EVI and one BT per MAC-VRF
with multiple VIDs representing that BD.
Jeffrey
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