From: Linda Dunbar <linda.dunbar@futurewei.com>
To: stefano previdi <stefano@previdi.net>
CC: "idr@ietf.org" <idr@ietf.org>,
 "draft-ietf-idr-segment-routing-te-policy@ietf.org"
 <draft-ietf-idr-segment-routing-te-policy@ietf.org>
Thread-Topic: Is the SR Policy SAFI described in
 draft-ietf-idr-segment-routing-te-policy-07 under the MP-NLRI (code =14) or
 under the Tunnel Path attribute (code = 23)?
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Date: Wed, 23 Oct 2019 14:40:17 +0000
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Archived-At: <https://mailarchive.ietf.org/arch/msg/idr/1ncWXJgMZaz2zKXpPlk5CDx5m2s>
Subject: Re: [Idr] Is the SR Policy SAFI described in
 draft-ietf-idr-segment-routing-te-policy-07 under the MP-NLRI (code =14) or
 under the Tunnel Path attribute (code = 23)?
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Stefano,=20

Since the MP-NLRI Path Attribute (code=3D14) and the Tunnel Path Attribute =
(code =3D23) are at the same level, does it mean that one BGP UPDATE can on=
ly carry one policy?=20

I am just curious why not encoding the Policy Content as subTLVs nested wit=
hin the Policy Identifier encoded in the MP-NLRI? So that one BGP UPDATE ca=
n carry multiple SR policies.

Thanks, Linda

-----Original Message-----
From: stefano previdi <stefano@previdi.net>=20
Sent: Wednesday, October 23, 2019 4:05 AM
To: Linda Dunbar <linda.dunbar@futurewei.com>
Cc: idr@ietf.org; draft-ietf-idr-segment-routing-te-policy@ietf.org
Subject: Re: Is the SR Policy SAFI described in draft-ietf-idr-segment-rout=
ing-te-policy-07 under the MP-NLRI (code =3D14) or under the Tunnel Path at=
tribute (code =3D 23)?


> On Oct 23, 2019, at 1:23 AM, Linda Dunbar <linda.dunbar@futurewei.com> wr=
ote:
>=20
> IDR experts and the Authors of draft-ietf-idr-segment-routing-te-policy-0=
7:
> =20
> The section 2.1 of draft-ietf-idr-segment-routing-te-policy-07 describes =
a new SR Policy SAFI under NLRI of BGP UPDATE to advertise SR policies.
> =20
> Does it mean that SR Policy SAFI is under the MP-NLRI Path Attribute (Cod=
e =3D 14)?


yes, the nlri with the new safi identifies the policy:
   +------------------+
   |  NLRI Length     | 1 octet
   +------------------+
   |  Distinguisher   | 4 octets
   +------------------+
   |  Policy Color    | 4 octets
   +------------------+
   |  Endpoint        | 4 or 16 octets=20
   +------------------+


> The Section 2.2 indicates that SR Policy is encoded in the Tunnel Encapsu=
lation Path Attribute defined in the draft-ietf-idr-tunnel-encaps-12.
> =20
> Does it mean the SR policy is also under the Tunnel Path Attribute with C=
ode =3D23?


the content (i.e., the details) of the sr policy is encoded in the tunnel p=
ath attribute.


> Can you please explain is it MP-NLRI Path Attribute or Tunnel Encap Path =
Attribute that SR policy are encoded?


there are separate items: policy identifier and policy content.

the policy identifier (distinguisher, color, endpoint) goes into the nlri a=
nd the policy content (e.g., the segment list) go into the tunnel path attr=
ibute.

s.


> =20
> Thank you very much.=20
> =20
> Linda Dunbar