Subject: multi-domain VPLS question (draft-ietf-l2vpn-vpls-ldp-03)

From: "Dror Caspi" <[email-masked]>
Date: Tue, 4 May 2004 17:09:48 +0300

Hi,
 
Having read section 11.3 on multi-domain VPLS service, I see a problem with loop avoidance. 
 
To explain this, suppose we have 3 domains: A, B and C.   In domain A, border PE-rs named Ab connects to border PE-rs named Ba in domain B.  Likewise, we have PE-rs pairs Ac-Ca and Bc-Cb.
 
In the above example, it is easy to see that there is a potential loop.  What is not clear is how the split horizon forwarding rules in section 3 avoid those loops.
 
Suppose border PE-rs Ab received a frame from PE-rs Ac.  How would it tell whether this frame originated in domain A (from one of the CEs connected to Ac) or in domain C?
 
Or maybe I am mistaken and a border PE-rs is not allowed to serve CEs directly?  This is not stated in the draft.
 
Any comments are welcome
 
Dror

---

From: "Marc Lasserre" <[email-masked]>
Date: Tue, 4 May 2004 17:39:43 +0200

Dror,

A full mesh of inter-domain spokes must be created between border PE-rs's, not
between domains as implied in your example. Hence, within each domain one 
border PE-rs is selected, and a full mesh of spokes is created per VPLS instance
between these PE-rs's. Note that different border PE-rs's can be used for different 
VPLS instances.

Marc
  ----- Original Message ----- 
  From: Dror Caspi 
  To: [email-masked] 
  Sent: May 04, 2004 16:09
  Subject: multi-domain VPLS question (draft-ietf-l2vpn-vpls-ldp-03)

  Hi,

  Any comments are welcome

  Dror

---

From: Yakov Rekhter <[email-masked]>
Date: Wed, 05 May 2004 07:35:19 -0700

Marc,

> Dror,
> 
> A full mesh of inter-domain spokes must be created between border =
> PE-rs's, not between domains as implied in your example. Hence, within 
> each domain one border PE-rs is selected, and a full mesh of spokes 
> is created per VPLS instance between these PE-rs's. 

Couple of questions:
 
1. If a particular VPLS is present in 5 domains, and each domain elects
a border PE-rs for that VPLS, does the above mean that these 5 PE-rs'
have to have a full mesh of LDP sessions ?

2. What happens when the selected PE-rs crashes ?

Yakov.

> Note that different border PE-rs's can be used =
> for different=20
> VPLS instances.
> 
> Marc
>   ----- Original Message -----=20
>   From: Dror Caspi=20
>   To: [email-masked]=20
>   Sent: May 04, 2004 16:09
>   =20
>   Having read section 11.3 on multi-domain VPLS service, I see a problem =
> with loop avoidance.=20
> 
>   =20
> 
>   To explain this, suppose we have 3 domains: A, B and C.   In domain A, =
> border PE-rs named Ab connects to border PE-rs named Ba in domain B.  =
> Likewise, we have PE-rs pairs Ac-Ca and Bc-Cb.
> 
>   =20
> 
>   In the above example, it is easy to see that there is a potential =
> loop.  What is not clear is how the split horizon forwarding rules in =
> section 3 avoid those loops.
> 
>   =20
> 
>   Suppose border PE-rs Ab received a frame from PE-rs Ac.  How would it =
> tell whether this frame originated in domain A (from one of the CEs =
> connected to Ac) or in domain C?
> 
>   =20
> 
>   Or maybe I am mistaken and a border PE-rs is not allowed to serve CEs =
> directly?  This is not stated in the draft.
> 
>   =20
> 
>   Any comments are welcome
> 
>   =20
> 
>   Dror
> 
>   =20
> 
>   =20
> 
>   =20
> 
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> <DIV><FONT size=3D2>Dror,</FONT></DIV>
> <DIV><FONT size=3D2></FONT>&nbsp;</DIV>
> <DIV><FONT size=3D2>A full mesh of inter-domain spokes must be created =
> between=20
> border PE-rs's, not</FONT></DIV>
> <DIV><FONT size=3D2>between domains as implied in your example. Hence,=20
> w</FONT><FONT size=3D2>ithin each domain one =
> <BR>border&nbsp;</FONT><FONT=20
> size=3D2>PE-rs is selected, and a full mesh of spokes </FONT><FONT =
> size=3D2>is=20
> created per VPLS instance</FONT></DIV>
> <DIV><FONT size=3D2>between these PE-rs's. </FONT><FONT size=3D2>Note =
> that different=20
> border PE-rs's can be used for </FONT><FONT size=3D2>different =
> </FONT></DIV>
> <DIV><FONT size=3D2>VPLS instances.</FONT></DIV>
> <DIV><FONT size=3D2></FONT>&nbsp;</DIV>
> <DIV><FONT size=3D2>Marc</FONT></DIV>
> <BLOCKQUOTE dir=3Dltr=20
> style=3D"PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; =
> BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
>   <DIV style=3D"FONT: 10pt arial">----- Original Message ----- </DIV>
>   <DIV=20
>   style=3D"BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: =
> black"><B>From:</B>=20
>   <A title=[email-masked] =
> href=3D"mailto:[email-masked]">Dror=20
>   Caspi</A> </DIV>
>   <DIV style=3D"FONT: 10pt arial"><B>To:</B> <A title=[email-masked]=20
>   href=3D"mailto:[email-masked]">[email-masked]</A> </DIV>
>   <DIV style=3D"FONT: 10pt arial"><B>Sent:</B> May 04, 2004 16:09</DIV>
>   <DIV style=3D"FONT: 10pt arial"><B>Subject:</B> multi-domain VPLS =
> question=20
>   (draft-ietf-l2vpn-vpls-ldp-03)</DIV>
>   <DIV><BR></DIV>
>   <DIV class=3DSection1>
>   <P class=3DMsoNormal><SPAN class=3DEmailStyle15><FONT face=3DArial =
> color=3Dblack=20
>   size=3D2><SPAN=20
>   style=3D"FONT-SIZE: 10pt; FONT-FAMILY: =
> Arial">Hi,<o:p></o:p></SPAN></FONT></SPAN></P>
>   <P class=3DMsoNormal><SPAN class=3DEmailStyle15><FONT face=3DArial =
> color=3Dblack=20
>   size=3D2><SPAN style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Arial"><![if =
> !supportEmptyParas]><![endif]>&nbsp;<o:p></o:p></SPAN></FONT></SPAN></P>
>   <P class=3DMsoNormal><SPAN class=3DEmailStyle15><FONT face=3DArial =
> color=3Dblack=20
>   size=3D2><SPAN style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Arial">Having =
> read section=20
>   11.3 on multi-domain VPLS service, I see a problem with loop =
> avoidance.=20
>   <o:p></o:p></SPAN></FONT></SPAN></P>
>   <P class=3DMsoNormal><SPAN class=3DEmailStyle15><FONT face=3DArial =
> color=3Dblack=20
>   size=3D2><SPAN style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Arial"><![if =
> !supportEmptyParas]><![endif]>&nbsp;<o:p></o:p></SPAN></FONT></SPAN></P>
>   <P class=3DMsoNormal><SPAN class=3DEmailStyle15><FONT face=3DArial =
> color=3Dblack=20
>   size=3D2><SPAN style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Arial">To =
> explain this,=20
  suppose we have 3 domains: A, B and C.<SPAN=20
>   style=3D"mso-spacerun: yes">&nbsp;&nbsp; </SPAN>In domain A, border =
> PE-rs named=20
>   Ab connects to border PE-rs named Ba in domain B.<SPAN=20
>   style=3D"mso-spacerun: yes">&nbsp; </SPAN>Likewise, we have PE-rs =
> pairs Ac-Ca=20
>   and Bc-Cb.<o:p></o:p></SPAN></FONT></SPAN></P>
>   <P class=3DMsoNormal><SPAN class=3DEmailStyle15><FONT face=3DArial =
> color=3Dblack=20
>   size=3D2><SPAN style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Arial"><![if =
> !supportEmptyParas]><![endif]>&nbsp;<o:p></o:p></SPAN></FONT></SPAN></P>
>   <P class=3DMsoNormal><SPAN class=3DEmailStyle15><FONT face=3DArial =
> color=3Dblack=20
>   size=3D2><SPAN style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Arial">In the =
> above example,=20
>   it is easy to see that there is a potential loop.<SPAN=20
>   style=3D"mso-spacerun: yes">&nbsp; </SPAN>What is not clear is how the =
> split=20
>   horizon forwarding rules in section 3 avoid those=20
>   loops.<o:p></o:p></SPAN></FONT></SPAN></P>
>   <P class=3DMsoNormal><SPAN class=3DEmailStyle15><FONT face=3DArial =
> color=3Dblack=20
>   size=3D2><SPAN style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Arial"><![if =
> !supportEmptyParas]><![endif]>&nbsp;<o:p></o:p></SPAN></FONT></SPAN></P>
>   <P class=3DMsoNormal><SPAN class=3DEmailStyle15><FONT face=3DArial =
> color=3Dblack=20
>   size=3D2><SPAN style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Arial">Suppose =
> border PE-rs=20
>   Ab received a frame from PE-rs Ac.<SPAN style=3D"mso-spacerun: =
> yes">&nbsp;=20
>   </SPAN>How would it tell whether this frame originated in domain A =
> (from one=20
>   of the CEs connected to Ac) or in domain=20
> C?<o:p></o:p></SPAN></FONT></SPAN></P>
>   <P class=3DMsoNormal><SPAN class=3DEmailStyle15><FONT face=3DArial =
> color=3Dblack=20
>   size=3D2><SPAN style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Arial"><![if =
> !supportEmptyParas]><![endif]>&nbsp;<o:p></o:p></SPAN></FONT></SPAN></P>
>   <P class=3DMsoNormal><SPAN class=3DEmailStyle15><FONT face=3DArial =
> color=3Dblack=20
>   size=3D2><SPAN style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Arial">Or maybe =
> I am=20
>   mistaken and a border PE-rs is not allowed to serve CEs directly?<SPAN =
> 
>   style=3D"mso-spacerun: yes">&nbsp; </SPAN>This is not stated in the=20
>   draft.<o:p></o:p></SPAN></FONT></SPAN></P>
>   <P class=3DMsoNormal><SPAN class=3DEmailStyle15><FONT face=3DArial =
> color=3Dblack=20
>   size=3D2><SPAN style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Arial"><![if =
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> color=3Dblack=20
  size=3D2><SPAN style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Arial">Any =
> comments are=20
>   welcome<o:p></o:p></SPAN></FONT></SPAN></P>
>   <P class=3DMsoNormal><SPAN class=3DEmailStyle15><FONT face=3DArial =
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>   size=3D2><SPAN style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Arial"><![if =
> !supportEmptyParas]><![endif]>&nbsp;<o:p></o:p></SPAN></FONT></SPAN></P><=
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---

From: "Marc Lasserre" <[email-masked]>
Date: Wed, 5 May 2004 17:24:56 +0200

> have to have a full mesh of LDP sessions ?

Yes, it does.

> 2. What happens when the selected PE-rs crashes ?

This would result in LDP adjacencies within the corresponding domain and
between domains to be dropped, and hence would trigger an alarm indicating
loss of connectivity for the corresponding VPLS instances. As I replied in a
previous email, "A future draft could specify how redundant inter-domain
connectivity is achieved (election of border PE, and protocol between PEs
within one domain to indicate loss of connectivity)."

Marc