Subject: Re: [bess] handling DAD in draft-ietf-bess-evpn-inter-subnet-forwarding-05

From: "Ali Sajassi (sajassi)" <[email-masked]>
Date: Thu, 31 Jan 2019 02:20:51 +0000

Please refer to my reply inline marked with "AS>"

On 9/17/18, 3:47 PM, "BESS on behalf of Sowmini Varadhan" <[email-masked] on behalf of [email-masked]> wrote:

    hi,
    
    I have a question about Section 4.1.1 ("Initiating an APR Request upon a Move")
    in draft-ietf-bess-evpn-inter-subnet-forwarding-05 which has the paragraph:
    
    "Since this NVE has previously learned the same MAC and IP addresses
     from the source NVE, it recognizes that there has been a MAC move and
     it initiates MAC mobility procedures per [RFC7432] by advertising an
     EVPN MAC/IP route with both the MAC and IP addresses filled in along
     with MAC Mobility Extended Community with the sequence number
     incremented by one."
    
    but the Grat ARP may be an indication of a duplicate address, or it
    may have been manufactured  by a malicious node, in which case this is not
    a mac-move.
    
    Should the target NVE first check with the src NVE that the
    original (ip, mac) binding does not exist at the source NVE
    before advertising the MAC route?

AS> RFC 7431 has procedures for duplicate MAC address detection.
    
    The next paragraph in Section 4.1.1 says
    "The source NVE upon receiving this MAC/IP advertisement, realizes
     that the MAC has moved to the target NVE. It updates its MAC-VRF and
     IP-VRF table accordingly with the adjacency information of the target
     NVE and withdraws its EVPN MAC/IP route. Furthermore, it sends an ARP
     probe locally to ensure that the MAC is gone and it deletes its ARP
     entry corresponding to that <IP, MAC> when there is no ARP response."
    
    One minor nit here is that the ARP probe should really check that
    the IP address is gone (i.e. the IP address is not duplicate),
    and this check should be done *before* the target NVE gets to declare
    that the TS has moved?

AS>  If ARP probing is done before the target NVE gets to declare that the TS has moved, then the MAC move is delayed unnecessarily for ALL the legitimate MAC move cases which in turn can cause some loss of traffic and degradation in service. It should be noted that the MAC move procedures in here is consistent with RFC 7432.
    
    (same thing for section 4.1.2, where the target NVE learns the
    <IP, MAC> at the new location from the data packet without an
    intervening GARP)

AS> same reply as  above.
    
    Thanks
    --Sowmini
    
    _______________________________________________
    BESS mailing list
    [email-masked]
    https://urldefense.proofpoint.com/v2/url?u=https-3A__www.ietf.org_mailman_listinfo_bess&d=DwICAg&c=HAkYuh63rsuhr6Scbfh0UjBXeMK-ndb3voDTXcWzoCI&r=f7wsLGcfzAWDNS6XNTBZwj_OLAOsZZqdrR2IDAzeZqE&m=7BzJkC9LubpFLLA9w_G3DK1kNzgduhVEcOWaw7e3qaw&s=afaJR-F-EDZgb60cwn8DLxnZNeRUtBoT4GbCGfk5B8I&e=

---

From: Sowmini Varadhan <[email-masked]>
Date: Thu, 31 Jan 2019 04:39:32 -0500

On Wed, Jan 30, 2019 at 9:20 PM Ali Sajassi (sajassi) [email-masked] wrote:

sajassi> AS> RFC 7431 has procedures for duplicate MAC address detection.

rfc 7431 is the Informational RFC titled "Multicast-Only Fast Reroute".

Perhaps you mean rfc 7432. And I suspect you mean Section 15.1

draft*evpn-inter-subnet-forwarding should call out this cross-reference
explicitly, so that the reader does not have to speculate (as I
just did)

sajassi> AS> If ARP probing is done before the target NVE gets to
declare that the TS has moved, then the MAC move is delayed
unnecessarily for ALL the legitimate MAC move cases which in turn can
cause some loss of traffic and degradation in service. It should be
noted that the MAC move procedures in here is consistent with RFC
7432.
sajassi> AS> same reply as above.

it's a bit odd that lot of chaos can happen for approx 3 mins
when there is actually a duplicate address (created accidentally
or maliciously) but I suppose you could say that this is already
based on 7431, so not something introduced by
draft*evpn-inter-subnet-forwarding

Thanks
--Sowmini