| PCE Working Group | D. Dhody |
| Internet-Draft | U. Palle |
| Intended status: Standards Track | Huawei Technologies India Pvt Ltd |
| Expires: February 24, 2014 | August 23, 2013 |
OSPF Protocol Extensions for Boundary Node Discovery (BND)
draft-dhody-pce-bn-discovery-ospf-07
The Path Computation Element (PCE) may be used for computing multi-domain (Area or AS) Multiprotocol Label Switching (MPLS) and Generalized MPLS (GMPLS) Traffic Engineered (TE) Label Switch Path (LSP).
In this circumstance, it is highly desirable to be able to dynamically and automatically discover a set of Boundary Nodes (BN) along with their domain information in a simple way. For that purpose, this document defines extensions to the Open Shortest Path First (OSPF) routing protocol for the advertisement of Boundary Node (BN) Discovery information within an OSPF area or within the entire OSPF routing domain.
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This document defines extensions to OSPFv2 [RFC2328] and OSPFv3 [RFC5340] to allow a boundary node in an OSPF routing domain to advertise its location, along with domain information.
Generic capability advertisement mechanisms for OSPF are defined in [RFC4970]. These allow a router to advertise its capabilities within an OSPF area or an entire OSPF routing domain. This document leverages this generic capability advertisement mechanism to fully satisfy the dynamic BN discovery.
This document defines a new TLV (named the Boundary Node Discovery TLV (BND TLV)) to be carried within the OSPF Router Information LSA ([RFC4970]).
The Boundary Node information advertised is detailed in Section 6. Protocol extensions and procedures are defined in Section 7 and Section 8.
A detailed description about the need for auto discovery of Boundary Nodes (BN) and thier domains is also provided in this document.
The OSPF extensions defined in this document allow for Boundary Node discovery within an OSPF routing domain. Boundary Node can be an Area Border Router (ABR) or Autonomous System Border Router (ASBR).
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].
The following terminology is used in this document.
Backward Recursive Path Computation (BRPC) procedure as defined in [RFC5441], requires Path Computation Element (PCE) [RFC4655] to be aware of the Boundary Nodes (BN) for the inter-domain path computation. This information would be either statically configured at PCE or learned via some mechanism, as listed in Section 4.
In case of static configuration, as shown in the Figure 1, incase of OSPF Area0, configuration of BNs at PCE5 is extensive. BRPC procedure guarantees a best path only if BNs are selected correctly, any change in BNs at run time may lead to sub-optimal path. Also Administrator need to configure ABR / ASBR ID in such a way that it is reachable from all the domains, BND TLV can take care of this automatically.
+--------------------+
| +-----+|
| Area 2 | PCE2||
| +-----+|
| |
| |
| BN4+----+ |
+--------+----+------+
+----------+----+---------+
| +----+ |
| |
| |
| |
+---------------+ | |+----------------+
| BN1 | | || BN5 |
| +-+-++ +++--+ |
| | | || ||| | |
| +-+-++ +++--+ |
| | | || |
| BN2 | | || BN6 |
| +-+-++ Area 0 +++--+ |
| Area 1 | | || ||| | Area 3 |
| +-+-++ +++--+ |
| | | || |
| BN3 | | +-----+ || BN7 |
|+-----+ +-+-++ | PCE5| +++--+ +-----+ |
|| PCE1| | | || +-----+ ||| | | PCE3| |
|+-----+ +-+-++ +++--+ +-----+ |
| | | || |
+---------------+ | |+----------------+
| |
| |
| +----+ |
+----------+----+---------+
+--------+----+------+
| BN8 +----+ |
| |
| |
| Area 4 +-----+|
| | PCE4||
| +-----+|
+--------------------+
Figure 1: OSPF Area Topology
The problems with existing mechanism to discover Boundary nodes are listed in Section 4.
Hierarchal PCE (H-PCE) [RFC6805] mechanim MAY require a parent PCE to be aware of child domain's boundary node, child PCE in any case should be aware of all its boundary nodes and can use mechnims as described in this document.
|
| +-------------+ +----------------+
| |Area 2 | |Area 4 |
| | +--+| | +--+ |
| | | || | | | |
| | +--+ +--+| | +--+ +--+ |
| | | | | | | | |
| | *--+ | | +--+ |
| | / +--+ | | +--+ |
| |/ | | | | | | |
| / +--+ | | +--+ +--+ |
| /| +--+ |+--------------+| | | |
|/ | | | ++-+ +-++ +--+ |
+-------------+/ | +--+ || | | || |
| /| | ++-+ +-++ |
| +--*|| +-------------+| |+----------------+
| | ||| | +--+ |
| +--+|| | | | |
| +--+ || | +--+ |
| | | || | |
| +--+ || | |
| || | +--+ |
|+--+ || | | | |
|| | || | +--+ |
|+--+ || | |
| || | +--+ |
| +--+ || +------------+ | | | |+----------------+
| | | || |Area 3 +-++ +--+ +-++ Area 5 |
| +--+ || | | || | || |
| || | +-++ +-++ |
| +--+|| | +--+ | | Area 0 || +--+ |
| | ||| | | | | +--------------+| | | |
| +--*|| | +--+ | | +--+ |
| \| | | | +--+ |
|Area 1 |\ | +--+ | | +--+ | | |
+-------------+|\ | | | | | | | +--+ |
| \| +--+ +--+ | +--+ |
| \ | | | |
| |\ +--+ | +--+ |
| | \ +--+ | | | | |
| | \| | | | +--+ |
| | *--+ | | |
| | | | |
| +------------+ +----------------+
|
|
As 100 | AS 200
|
. .
. Area 0 .
+--+ +--+
..|R1|.. ..|R2|..
. +--+ .. +--+ .
. .. .
. +--+ .
. Area1 |R3| Area2 .
. +--+ +--+ .
. .. |R4| .
. . . +--+ .
....... .......
A simple solution would be to configure BNs (ABR and ASBR) at PCE(s) along with their domain information. As this information is fairly static this could work in simple situations. But as PCE are being used in bigger and multiple domains, any sort of static configurations would put extra effort on the system administrator. Selection of correct BNs is the core of any inter-domain path computation procedure, this information should be dynamically learned and maintained.
There are methods to learn BNs dynamically from IGP, but the knowledge of neighboring-domains is not possible to obtain. Without this the correct BN based on the domain-path can not be selected. [RFC5441] mentions:
"Note that PCE(i) only considers the entry BNs of domain(i), i.e., only the BNs that provide connectivity from domain(i-1). In other words, the set BN-en(k,i) is only made of those BNs that provide connectivity from domain (i-1) to domain(i)."
This selection of correct BNs providing connectivity between correct domains cannot be made by the information obtained from IGP. Without the correct selection we would not be following [RFC5441].
[DOMAIN-SEQ] provides a standard representation of Domain Sequence in all deployment scenarios. The Domain Information carried in the BN-DOMAIN sub-tlv is same as the sub-objects inside the domain sequence.
The BN discovery information is composed of:
Changes in BN discovery information may occur as a result of BN configuration update or domain status change.
The flooding scope for BN information advertised through OSPF can be limited to OSPF area(s) the BN belongs to, or can be extended across the entire OSPF routing domain.
The OSPF BN Discovery TLV (BND TLV) contains a non-ordered set of sub-TLVs.
The format of the OSPF BND TLV and its sub-TLVs is identical to the TLV format used by the Traffic Engineering Extensions to OSPF [RFC3630]. That is, the TLV is composed of 2 octets for the type, 2 octets specifying the TLV length, and a value field. The Length field defines the length of the value portion in octets.
The OSPF BND TLV has the following format:
1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | // sub-TLVs // | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: To be assigned by IANA (suggested value 8)
Length: Variable
Value: This comprises of following sub-TLVs
Two sub-TLVs are defined:
Sub-TLV type Length Name
1 variable BN-ADDRESS sub-TLV
2 4 BN-DOMAIN sub-TLV
The BN-ADDRESS and BN-DOMAIN sub-TLVs MUST always be present within the BND TLV.
Malformed BND TLVs or sub-TLVs not explicitly described in this document MUST cause the LSA to be treated as malformed according to the normal procedures of OSPF.
Any unrecognized sub-TLV MUST be silently ignored.
The BND TLV is carried within an OSPF Router Information LSA defined in [RFC4970].
The following sub-sections describe the sub-TLVs which are carried within the BND TLV.
The BN-ADDRESS sub-TLV specifies an IP address that can be used to reach the BN. It is RECOMMENDED to make use of an address that is always reachable, provided that the BN is alive and reachable.
The BN-ADDRESS sub-TLV is mandatory; it MUST be present within the BND TLV. It MAY appear twice, when the BN has both an IPv4 and IPv6 address. It MUST NOT appear more than once for the same address type. If it appears more than once for the same address type, only the first occurrence is processed and any others MUST be ignored.
The format of the BN-ADDRESS sub-TLV is as follows:
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 1 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| address-type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// BN IP Address //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
BN-ADDRESS sub-TLV format
Type: 1
Length: 8 (IPv4) or 20 (IPv6)
Address-type:
1 IPv4
2 IPv6
Reserved: SHOULD be set to zero on transmission and MUST be ignored on receipt.
BN IP Address: The IP address to be used to reach the BN.
The BN-DOMAIN sub-TLV specifies a BN-Domain (area or AS) where the BN has topology connectivity.
The BN-DOMAIN sub-TLV is mandatory; it MUST be present within the BND TLV.
A BND TLV MUST include two or more BN-DOMAIN sub-TLVs as the BN has connectivity into multiple BN-Domains.
The BN-DOMAIN sub-TLV has the following format:
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 2 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Domain-type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Domain ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
BN-DOMAIN sub-TLV format
Type: 2
Length: 8
Two domain-type values are defined:
1 OSPF Area ID
2 AS Number
Domain ID: With the domain-type set to 1, this indicates the 32-bit Area ID of an area where the BN (ABR) has connectivity. With domain-type set to 2, this indicates an AS number of an AS where the BN (ASBR) has connectivity. When the AS number is coded in two octets, the AS Number field MUST have its first two octets set to 0.
The BND TLV is advertised within OSPFv2 Router Information LSAs (Opaque type of 4 and Opaque ID of 0) or OSPFv3 Router Information LSAs (function code of 12), which are defined in [RFC4970]. As such, elements of procedure are inherited from those defined in [RFC4970].
In OSPFv2, the flooding scope is controlled by the opaque LSA type(as defined in [RFC5250]) and in OSPFv3, by the S1/S2 bits (as defined in [RFC5340]). If the flooding scope is area local, then the BND TLV MUST be carried within an OSPFv2 type 10 router information LSA or an OSPFV3 Router Information LSA with the S1 bit set and the S2 bit clear. If the flooding scope is the entire IGP domain, then the BND TLV MUST be carried within an OSPFv2 type 11 Router Information LSA or OSPFv3 Router Information LSA with the S1 bit clear and the S2 bit set.
When the BN function is deactivated, the OSPF speaker MUST originate a new Router Information LSA that no longer includes the corresponding BND TLV, provided there are other TLVs in the LSA. If there are no other TLVs in the LSA, it MUST either send an empty Router Information LSA or purge it by prematurely aging it.
The BN address (i.e., the address indicated within the BN-ADDRESS sub-TLV) SHOULD be reachable via some prefixes advertised by OSPF.
The BND TLV information regarding a specific BN is only considered current and useable when the router advertising this information is itself reachable via OSPF calculated paths in the same area of the LSA in which the BND TLV appears.
A change in the state of a BN (activate, deactivate, domain change) MUST result in a corresponding change in the BND TLV information advertised by an OSPF router (inserted, removed, updated)in its LSA. The way BNs determine the information they advertise, and how that information is made available to OSPF, is out of the scope of this document. Some information may be configured and other information may be automatically determined by the OSPF.
A change in information in the BND TLV MUST NOT trigger any SPF computation at a receiving router.
The BND TLV defined in this document does not introduce any interoperability issues.
A router not supporting the BND TLV will just silently ignore the TLV as specified in [RFC4970].
The routers acting as BNs will originate Opaque LSA with BND Tlv; As there are only few BNs exist in the network, the performance impact in flooding is very less.
IANA has defined a registry for TLVs carried in the Router Information LSA defined in [RFC4970]. A number of IANA considerations have been highlighted in previous sections of this document. IANA is requested to make the following allocations.
Value TLV Name Reference ----- -------- ---------- To be BND (this document) assigned by IANA
This document defines OSPF extensions for BN discovery within an administrative domain. Hence the security of the BN discovery relies on the security of OSPF.
Mechanisms defined to ensure authenticity and integrity of OSPF LSAs [RFC2154], and their TLVs, can be used to secure the BN Discovery information as well.
OSPF provides no encryption mechanism for protecting the privacy of LSAs and, in particular, the privacy of the BN discovery information.
TBD
We would like to thank Quintin Zhao, Daniel King, Adrian Ferral, Suresh babu, Pradeep Shastry, Saravana Kumar, Srinivasan and Venugopal Reddy for their useful comments and suggestions.
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. |