[bess] Re: Originating Router's IP Address in EVPN

[Muthu Arul Mozhi Perumal <[e-mail]>]

Searching further, it looks some vendors already support a configuration
option to set the Originating Router's IP address per EVI (with the default
being the PE loopback) for the IMET route. Given this, it is difficult to
understand the rationale behind this requirement
in draft-ietf-bess-rfc7432bis that says "it must remain the same for all
EVPN routes advertised by that PE (across all EVIs)."..

Now, it says "must" (not MUST), so could be ignored :)

Regards,
Muthu

On Tue, Mar 18, 2025 at 2:41 PM Muthu Arul Mozhi Perumal <
[e-mail]> wrote:

> Hi experts,
>
> Consider the foll. EVPN VPLS deployment scenario:
>
> PE1(EVI1)----IP/MPLS----PE2(EVI2, EVI3)
>
> EV11, EVI2 and EVI3 all use the same Ether Tag (assume VLAN based service
> for simplicity).
>
> EVI1 in PE1 imports the routes (i,e. RTs) from both EV2 and EV3 in PE2, so
> that EVI1 in PE1 has L2 reachability to both EV2 and EVI3 in PE2.
>
> However, looking at draft-ietf-bess-rfc7432bis, it looks this would be a
> problem for the IMET routes originated by PE2 for EVI2 and EVI3.
>
> Section 7.3 describes the IMET route format and says:
> <snip>
> For the purpose of BGP route key processing, only the Ethernet Tag ID, IP
> Address Length, and Originating Router's IP Address fields are considered
> to be part of the prefix in the NLRI.
> </snip>
>
> Then section 11.1 describes how the IMET is constructed and says:
> <snip>
> The Originating Router's IP Address field value MUST be set to an IP
> address of the PE (e.g., this address may be the PE's loopback address).
> The IP Address Length field is in bits. The Originating Router's IP address
> does not need to be a routable address and its purpose is to identify the
> originator of that EVPN route uniquely. It can be either IPv4 or IPv6
> address independent of the BGP next hop address type for that NLRI and it
> must remain the same for all EVPN routes advertised by that PE* across
> all EVIs*.
> </snip>
>
> Given that all EVIs use the same Ethernet TAG, for PE1 to be able to
> distinguish between the IMET routes originated by PE2 for EVI2 and EVI3
> while importing them into EVI1, the Originating Router's IP Address field
> should be different in those IMET routes. However,
> draft-ietf-bess-rfc7432bis does not allow it and requires the same
> Originating Router's IP Address be used by PE2. Why is such a restriction
> needed? Why can't PE2 use two different (non routable) Originating
> Router's IP Address for the IMET routes originated for EVI2 and EVI3?
>
> Regards,
> Muthu
>