Re: RFC5798

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When VRRP is enabled then the associated MAC address is alwaysfixed=C2=A000=
-00-5E-00-01-{VRID}. =C2=A0Whether there's a Master failover, ornetwork par=
tition and heal, etc. there's no change to the mapping andall client hosts =
should be consistent. =C2=A0No action is required.
The sole reason for the gratuitous ARP is to increase robustnessthe very fi=
rst time VRRP is enabled in the network. =C2=A0Prior to VRRPenable some cli=
ent hosts may have cached the router physicalMAC address. =C2=A0When VRRP i=
s then enabled the first Mastertransition triggers gratuitous ARP to encour=
age client hosts toflush the router physical MAC address if it's in their c=
ache.

--- On Thu, 10/14/10, Stephen Nadas <[email protected]> wrote:

From: Stephen Nadas <[email protected]>
Subject: Re: [VRRP] RFC5798
To: "Carl Petersen" <[email protected]>
Cc: "[email protected]" <[email protected]>
Date: Thursday, October 14, 2010, 9:10 AM

=0A=0A =0A =0A _filtered #yiv163395626 {=0Afont-family:Cambria Math;}=0A _f=
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6MsoHyperlink {=0ACOLOR:blue;TEXT-DECORATION:underline;}=0A#yiv163395626 A:=
visited {=0ACOLOR:purple;TEXT-DECORATION:underline;}=0A#yiv163395626 SPAN.y=
iv163395626MsoHyperlinkFollowed {=0ACOLOR:purple;TEXT-DECORATION:underline;=
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v163395626 DIV.yiv163395626WordSection1 {=0A}=0A=0A=0A =0AIMO =0Abetter to =
ask VRRP list than me, individually, =0ARegards,=0ASteve =0A
=0A=0A=0AFrom: Carl Petersen =0A[mailto:[email protected]]=20
Sent: Thursday, October 14, 2010 =0A11:13 AM
To: Stephen Nadas
Subject: =0ARFC5798

=0A=0A=0AStephen, I want to ask you a question about this RFC and the =0AVR=
RP protocol. Regarding section 6.4.3, bullet points (735) to =0A(765). =0A =
=C2=A0 =0AIf 2 vrrp routers became isolated for whatever reason, one =0Arou=
ter would remain as master, the other would transition from backup to maste=
r =0Aand send a gratuitous arp (ipv4 only) to notify remote arp caches. My =
question =0Ais about when the fault is corrected. One router transitions fr=
om master to =0Abackup; the other router still remains as master. The backu=
p router follows =0A(735) to (765), but the master seemingly does nothing a=
t all. In particular the =0Anow-for-real master does not send a gratuitous =
arp. This leaves remote arp =0Acaches with the wrong ip/mac value. =0A =C2=
=A0 =0AI=E2=80=99m sure this has been considered. What is typically done to=
 =0Aprevent this scenario or to recover from it? =0A =C2=A0 =0AThanks =0A =
=C2=A0 =0ACarl Petersen =0A=C2=A0 =0A
-----Inline Attachment Follows-----

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<table cellspacing=3D"0" cellpadding=3D"0" border=3D"0" ><tr><td valign=3D"=
top" style=3D"font: inherit;">When VRRP is enabled then the associated MAC =
address is always<div>fixed&nbsp;00-00-5E-00-01-{VRID}. &nbsp;Whether there=
's a Master failover, or</div><div>network partition and heal, etc. there's=
 no change to the mapping and</div><div>all client hosts should be consiste=
nt. &nbsp;No action is required.</div><div><br></div><div>The sole reason f=
or the gratuitous ARP is to increase robustness</div><div>the very first ti=
me VRRP is enabled in the network. &nbsp;Prior to VRRP</div><div>enable som=
e client hosts may have cached the router physical</div><div>MAC address. &=
nbsp;When VRRP is then enabled the first Master</div><div>transition trigge=
rs gratuitous ARP to encourage client hosts to</div><div>flush the router p=
hysical MAC address if it's in their cache.</div><div><br></div><div><br>--=
- On <b>Thu, 10/14/10, Stephen Nadas
 <i>&lt;[email protected]&gt;</i></b> wrote:<br><blockquote style=
=3D"border-left: 2px solid rgb(16, 16, 255); margin-left: 5px; padding-left=
: 5px;"><br>From: Stephen Nadas &lt;[email protected]&gt;<br>Subje=
ct: Re: [VRRP] RFC5798<br>To: "Carl Petersen" &lt;[email protected]&g=
t;<br>Cc: "[email protected]" &lt;[email protected]&gt;<br>Date: Thursday, October =
14, 2010, 9:10 AM<br><br><div id=3D"yiv163395626">=0A=0A =0A =0A<style> _fi=
ltered #yiv163395626 {=0Afont-family:Cambria Math;}=0A _filtered #yiv163395=
626 {=0Afont-family:Calibri;}=0A _filtered #yiv163395626 {margin:1.0in 1.0i=
n 1.0in 1.0in;}=0A#yiv163395626 P.yiv163395626MsoNormal {=0AFONT-SIZE:11pt;=
MARGIN:0in 0in 0pt;FONT-FAMILY:"sans-serif";}=0A#yiv163395626 LI.yiv1633956=
26MsoNormal {=0AFONT-SIZE:11pt;MARGIN:0in 0in 0pt;FONT-FAMILY:"sans-serif";=
}=0A#yiv163395626 DIV.yiv163395626MsoNormal {=0AFONT-SIZE:11pt;MARGIN:0in 0=
in 0pt;FONT-FAMILY:"sans-serif";}=0A#yiv163395626 A:link {=0ACOLOR:blue;TEX=
T-DECORATION:underline;}=0A#yiv163395626 SPAN.yiv163395626MsoHyperlink {=0A=
COLOR:blue;TEXT-DECORATION:underline;}=0A#yiv163395626 A:visited {=0ACOLOR:=
purple;TEXT-DECORATION:underline;}=0A#yiv163395626 SPAN.yiv163395626MsoHype=
rlinkFollowed {=0ACOLOR:purple;TEXT-DECORATION:underline;}=0A#yiv163395626 =
SPAN.yiv163395626EmailStyle17 {=0ACOLOR:windowtext;FONT-FAMILY:"sans-serif"=
;}=0A#yiv163395626 .yiv163395626MsoChpDefault {=0A}=0A#yiv163395626 DIV.yiv=
163395626WordSection1 {=0A}=0A</style>=0A=0A =0A<div><font face=3D"Arial" c=
olor=3D"#0000ff" size=3D"2"><span class=3D"yiv163395626882180916-14102010">=
IMO =0Abetter to ask VRRP list than me, individually, </span></font></div>=
=0A<div><font face=3D"Arial" color=3D"#0000ff" size=3D"2"><span class=3D"yi=
v163395626882180916-14102010">Regards,</span></font></div>=0A<div><font fac=
e=3D"Arial" color=3D"#0000ff" size=3D"2"><span class=3D"yiv1633956268821809=
16-14102010">Steve =0A</span></font></div><br>=0A<div class=3D"yiv163395626=
OutlookMessageHeader" lang=3D"en-us" dir=3D"ltr" align=3D"left">=0A<hr tabi=
ndex=3D"-1">=0A<font face=3D"Tahoma" size=3D"2"><b>From:</b> Carl Petersen =
=0A[mailto:[email protected]] <br><b>Sent:</b> Thursday, October 14, =
2010 =0A11:13 AM<br><b>To:</b> Stephen Nadas<br><b>Subject:</b> =0ARFC5798<=
br></font><br></div>=0A<div></div>=0A<div class=3D"yiv163395626WordSection1=
">=0A<p class=3D"yiv163395626MsoNormal">Stephen, I want to ask you a questi=
on about this RFC and the =0AVRRP protocol. Regarding section 6.4.3, bullet=
 points (735) to =0A(765).</p> =0A<p class=3D"yiv163395626MsoNormal"> &nbsp=
;</p> =0A<p class=3D"yiv163395626MsoNormal">If 2 vrrp routers became isolat=
ed for whatever reason, one =0Arouter would remain as master, the other wou=
ld transition from backup to master =0Aand send a gratuitous arp (ipv4 only=
) to notify remote arp caches. My question =0Ais about when the fault is co=
rrected. One router transitions from master to =0Abackup; the other router =
still remains as master. The backup router follows =0A(735) to (765), but t=
he master seemingly does nothing at all. In particular the =0Anow-for-real =
master does not send a gratuitous arp. This leaves remote arp =0Acaches wit=
h the wrong ip/mac value.</p> =0A<p class=3D"yiv163395626MsoNormal"> &nbsp;=
</p> =0A<p class=3D"yiv163395626MsoNormal">I=E2=80=99m sure this has been c=
onsidered. What is typically done to =0Aprevent this scenario or to recover=
 from it?</p> =0A<p class=3D"yiv163395626MsoNormal"> &nbsp;</p> =0A<p class=
=3D"yiv163395626MsoNormal">Thanks</p> =0A<p class=3D"yiv163395626MsoNormal"=
> &nbsp;</p> =0A<p class=3D"yiv163395626MsoNormal">Carl Petersen</p> =0A<p =
class=3D"yiv163395626MsoNormal">&nbsp;</p></div> =0A</div><br>-----Inline A=
ttachment Follows-----<br><br><div class=3D"plainMail">____________________=
___________________________<br>vrrp mailing list<br><a ymailto=3D"mailto:vr=
[email protected]" href=3D"/mc/[email protected]">[email protected]</a><br><=
a href=3D"https://www.ietf.org/mailman/listinfo/vrrp" target=3D"_blank">htt=
ps://www.ietf.org/mailman/listinfo/vrrp</a><br></div></blockquote></div></t=
d></tr></table>
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