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

Krzysztof Szarkowicz <kszarkowicz@gmail.com> Wed, 08 August 2018 17:55 UTC

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From: Krzysztof Szarkowicz <kszarkowicz@gmail.com>
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Date: Wed, 8 Aug 2018 19:55:41 +0200
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Subject: Re: [bess] new WGLC for draft-ietf-bess-evpn-inter-subnet-forwarding-05
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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.


* 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
   subnet.
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).

>> 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:

* 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. 


Thanks,
Krzysztof


> On 2018-Aug-08, at 16:03, stephane.litkowski@orange.com 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
>  
> [1] https://datatracker.ietf.org/doc/draft-ietf-bess-evpn-inter-subnet-forwarding/ <https://datatracker.ietf.org/doc/draft-ietf-bess-evpn-inter-subnet-forwarding/>
>  
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