Re: [bess] new WGLC for draft-ietf-bess-evpn-inter-subnet-forwarding-05

"Ali Sajassi (sajassi)" <> Tue, 29 January 2019 22:41 UTC

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From: "Ali Sajassi (sajassi)" <>
To: Krzysztof Szarkowicz <>, "" <>
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Thread-Topic: [bess] new WGLC for draft-ietf-bess-evpn-inter-subnet-forwarding-05
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Subject: Re: [bess] new WGLC for draft-ietf-bess-evpn-inter-subnet-forwarding-05
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Please refer to my reply inline.

From: BESS <> on behalf of Krzysztof Szarkowicz <>
Date: Wednesday, August 8, 2018 at 10:55 AM
To: "" <>
Cc: "" <>
Subject: Re: [bess] new WGLC for draft-ietf-bess-evpn-inter-subnet-forwarding-05

Hello working group,

I have two comments regarding section 3.1.

* Section 3.1. refers only to “ARP” or “ARP reply”. Given the fact, it is applicable to IPv6 as well, it should refer to ND NS/NA messages as well, I believe.

OK. Added ND NS along with ARP request  and ND NA along with ARP reply.

* In the last paragraph of Section 3.1:

>  Irrespective of using only the anycast address or both anycast and

   non-anycast addresses on the same IRB, when a TS sends an ARP request

   to the PE that is attached to, the ARP request is sent for the

   anycast IP address of the IRB interface associated with the TS's

If both anycast and non-anycast addresses are on the IRB, it is legitimate that TS sends NS/ARP request to resolve either anycast (e.g. to resolve IP address of default gateway configured on TS), or to resolve non-anycast (e.g. ping towards non-anycast address was initiated on TS). Therefore, presuming that TS sends ARP request to resolve only anycast IP is not fully correct, I believe. Thus, wording of this paragraph should cover two cases (NS/ARP request to resolve anycast, and NS/ARP request to resolve non-anycast IP).

TS is not supposed to use non-anycast addresses on the IRB interface because if OAM pinging is needed by the TS to the IRB interface, it can do that using anycast address. Non-anycast addresses are intended to be used by network operator for its OAM within the EVPN network.

>> the PE1 sends an ARP reply with the MACx which is the anycast

   MAC address of that IRB interface.
NA/ARP reply has multiple MAC related fields:

* Destination MAC (in Ethernet header)
* Source MAC (in Ethernet header)
* Sender hardware address (in the payload)
* Target hardware address (in the payload)

It is not ultimately clear from the text, if 'Source MAC (in Ethernet header)’ or 'Sender hardware address (in the payload)’, or both, should be populated with MACx. As I see it, in case of both anycast and non-anycast address is used on IRB, the behavior should be:

Since we are talking about only anycast addresses to be used by the TS, then it should be clear that only anycast MAC address will be used  - i.e., in both source MAC (in Ethernet header) and Sender hardware address (in the payload). However to make that crystal clear, I modified the 1st half of the last para as follow:
“Irrespective of using only the anycast address or both anycast and non-anycast addresses on the same IRB, when a TS sends an ARP request or ND Neighbor Solicitation (NS) to the PE that is attached to, the request is sent for the anycast IP address of the IRB interface associated with the TS's subnet and the reply will use anycast MAC address (in both Source MAC in the Ethernet header and Sender hardware address in the payload).”


* TS sends and NS/ARP request for the anycast address:
   -> PE sends and NA/ARP reply with anycast MAC in both 'Source MAC (in Ethernet header)’ and 'Sender hardware address (in the payload)’ fields

* TS sends and NS/ARP request for the non-anycast address:
   -> PE sends and NA/ARP reply with non-anycast MAC in both 'Source MAC (in Ethernet header)’ and 'Sender hardware address (in the payload)’ fields

Otherwise, if only 'Sender hardware address (in the payload)’ is populated with anycast/non-anycast MAC (depending, which IP address is being resolved), and 'Source MAC (in Ethernet header)’  is always populated with no-anycast MAC (in implementations mimicking RFC 5798, Section 8.1.2/8.2.2/8.2.3 behavior, which explicitly disables usage of V-MAC in the 'Source MAC (in Ethernet header)’), the L2 domain (L2 switches) between PE and CE will not learn anycast MAC, thus resulting in unknown unicast flooding being used on these switches to reach anycast MAC. This is undesirable behavior and should be avoided.


On 2018-Aug-08, at 16:03,<> wrote:

Hello working group,

This email starts a two-week Working Group Last Call on draft-ietf-bess-evpn-inter-subnet-forwarding-05 [1].

A significant amount of update has been introduced since the previous WGLC. Please review the updates and provide your feedback.

This poll runs until *the 22th of August*.

Thank you

Stéphane, Matthew
bess chairs



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