Internet DRAFT - draft-ietf-i2rs-rib-info-model
draft-ietf-i2rs-rib-info-model
Network Working Group N. Bahadur, Ed.
Internet-Draft Uber
Intended status: Informational S. Kini, Ed.
Expires: November 8, 2018
J. Medved
Cisco
May 7, 2018
Routing Information Base Info Model
draft-ietf-i2rs-rib-info-model-17
Abstract
Routing and routing functions in enterprise and carrier networks are
typically performed by network devices (routers and switches) using a
routing information base (RIB). Protocols and configuration push
data into the RIB and the RIB manager installs state into the
hardware for packet forwarding. This draft specifies an information
model for the RIB to enable defining a standardized data model, and
it was used by the IETF's I2RS WG to design the I2RS RIB data model.
It is being published to record the higher-level informational model
decisions for RIBs so that other developers of RIBs may benefit from
the design concepts.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on November 8, 2018.
Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Conventions used in this document . . . . . . . . . . . . 5
2. RIB data . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1. RIB definition . . . . . . . . . . . . . . . . . . . . . . 6
2.2. Routing instance . . . . . . . . . . . . . . . . . . . . . 6
2.3. Route . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.4. Nexthop . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.4.1. Base nexthop . . . . . . . . . . . . . . . . . . . . . 12
2.4.2. Derived nexthops . . . . . . . . . . . . . . . . . . . 13
2.4.3. Nexthop indirection . . . . . . . . . . . . . . . . . 15
3. Reading from the RIB . . . . . . . . . . . . . . . . . . . . . 15
4. Writing to the RIB . . . . . . . . . . . . . . . . . . . . . . 15
5. Notifications . . . . . . . . . . . . . . . . . . . . . . . . 16
6. RIB grammar . . . . . . . . . . . . . . . . . . . . . . . . . 16
6.1. Nexthop grammar explained . . . . . . . . . . . . . . . . 19
7. Using the RIB grammar . . . . . . . . . . . . . . . . . . . . 19
7.1. Using route preference . . . . . . . . . . . . . . . . . . 19
7.2. Using different nexthops types . . . . . . . . . . . . . . 20
7.2.1. Tunnel nexthops . . . . . . . . . . . . . . . . . . . 20
7.2.2. Replication lists . . . . . . . . . . . . . . . . . . 20
7.2.3. Weighted lists . . . . . . . . . . . . . . . . . . . . 21
7.2.4. Protection . . . . . . . . . . . . . . . . . . . . . . 21
7.2.5. Nexthop chains . . . . . . . . . . . . . . . . . . . . 22
7.2.6. Lists of lists . . . . . . . . . . . . . . . . . . . . 23
7.3. Performing multicast . . . . . . . . . . . . . . . . . . . 24
8. RIB operations at scale . . . . . . . . . . . . . . . . . . . 25
8.1. RIB reads . . . . . . . . . . . . . . . . . . . . . . . . 25
8.2. RIB writes . . . . . . . . . . . . . . . . . . . . . . . . 25
8.3. RIB events and notifications . . . . . . . . . . . . . . . 25
9. Security Considerations . . . . . . . . . . . . . . . . . . . 25
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 26
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 26
12.1. Normative References . . . . . . . . . . . . . . . . . . . 26
12.2. Informative References . . . . . . . . . . . . . . . . . . 27
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 28
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1. Introduction
Routing and routing functions in enterprise and carrier networks are
traditionally performed in network devices. Traditionally routers
run routing protocols and the routing protocols (along with static
configuration information) populate the Routing Information Base
(RIB) of the router. The RIB is managed by the RIB manager and the
RIB manager provides a northbound interface to its clients, i.e., the
routing protocols, to insert routes into the RIB. The RIB manager
consults the RIB and decides how to program the Forwarding
Information Base (FIB) of the hardware by interfacing with the FIB
manager. The relationship between these entities is shown in
Figure 1.
+-------------+ +-------------+
|RIB client 1 | ...... |RIB client N |
+-------------+ +-------------+
^ ^
| |
+----------------------+
|
V
+---------------------+
| RIB manager |
| |
| +--------+ |
| | RIB(s) | |
| +--------+ |
+---------------------+
^
|
+---------------------------------+
| |
V V
+----------------+ +----------------+
| FIB manager 1 | | FIB manager M |
| +--------+ | .......... | +--------+ |
| | FIB(s) | | | | FIB(s) | |
| +--------+ | | +--------+ |
+----------------+ +----------------+
Figure 1: RIB manager, RIB clients, and FIB managers
Routing protocols are inherently distributed in nature and each
router makes an independent decision based on the routing data
received from its peers. With the advent of newer deployment
paradigms and the need for specialized applications, there is an
emerging need to guide the router's routing function [RFC7920].
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Traditional network-device protocol-based RIB population suffices for
most use cases where distributed network control is used. However
there are use cases that the network operators currently address by
configuring static routes, policies, and RIB import/export rules on
the routers. There is also a growing list of use cases in which a
network operator might want to program the RIB based on data
unrelated to just routing (within that network's domain).
Programming the RIB could be based on other information such as
routing data in the adjacent domain or the load on storage and
compute in the given domain. Or it could simply be a programmatic
way of creating on-demand dynamic overlays (e.g., GRE tunnels)
between compute hosts (without requiring the hosts to run traditional
routing protocols). If there was a standardized publicly-documented,
programmatic interface to a RIB, it would enable further networking
applications that address a variety of use cases [RFC7920].
A programmatic interface to the RIB involves 2 types of operations -
reading from the RIB and writing (adding/modifying/deleting) to the
RIB.
In order to understand what is in a router's RIB, methods like per-
protocol SNMP MIBs and screen scraping are used. These methods are
not scalable, since they are client pull mechanisms and not proactive
push (from the router) mechanisms. Screen scraping is error prone
(since the output format can change) and is vendor dependent.
Building a RIB from per-protocol MIBs is error prone since the MIB
data represent protocol data and not the exact information that went
into the RIB. Thus, just getting read-only RIB information from a
router is a hard task.
Adding content to the RIB from a RIB client can be done today using
static configuration mechanisms provided by router vendors. However
the mix of what can be modified in the RIB varies from vendor to
vendor and the method of configuring it is also vendor dependent.
This makes it hard for a RIB client to program a multi-vendor network
in a consistent and vendor-independent way.
The purpose of this draft is to specify an information model for the
RIB. Using the information model, one can build a detailed data
model for the RIB. That data model could then be used by a RIB
client to program a network device. One data model that has been
based on this draft is the I2RS RIB data model
[I-D.ietf-i2rs-rib-data-model].
The rest of this document is organized as follows. Section 2 goes
into the details of what constitutes and can be programmed in a RIB.
Guidelines for reading and writing the RIB are provided in Section 3
and Section 4 respectively. Section 5 provides a high-level view of
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the events and notifications going from a network device to a RIB
client, to update the RIB client on asynchronous events. The RIB
grammar is specified in Section 6. Examples of using the RIB grammar
are shown in Section 7. Section 8 covers considerations for
performing RIB operations at scale.
1.1. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. RIB data
This section describes the details of a RIB. It makes forward
references to objects in the RIB grammar (Section 6). A high-level
description of the RIB contents is as shown in Figure 2. Please note
that for ease of ASCII art representation this drawing shows a single
routing-instance, a single RIB, and a single route. Sub-sections of
this section describe the logical data nodes that should be contained
within a RIB. Section 3 and Section 4 describe the high-level read
and write operations.
network-device
|
| 0..N
|
routing-instance(s)
| |
| |
0..N | | 0..N
| |
interface(s) RIB(s)
|
|
| 0..N
|
route(s)
Figure 2: RIB model
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2.1. RIB definition
A RIB, in the context of the RIB information model, is an entity that
contains routes. It is identified by its name and is contained
within a routing instance (Section 2.2). A network device MAY
contain routing instances and each routing instance MAY contain RIBs.
The name MUST be unique within a routing instance. All routes in a
given RIB MUST be of the same address family (e.g., IPv4). Each RIB
MUST belong to a routing instance.
A routing instance may contain two or more RIBs of the same address
family (e.g., IPv6). A typical case where this can be used is for
multi-topology routing ([RFC4915], [RFC5120]).
Each RIB MAY be associated with an ENABLE_IP_RPF_CHECK attribute that
enables REVERSE PATH FORWARDING (RPF) checks on all IP routes in that
RIB. The RPF check is used to prevent spoofing and limit malicious
traffic. For IP packets, the IP source address is looked up and the
RPF interface(s) associated with the route for that IP source address
is found. If the incoming IP packet's interface matches one of the
RPF interface(s), then the IP packet is forwarded based on its IP
destination address; otherwise, the IP packet is discarded.
2.2. Routing instance
A routing instance, in the context of the RIB information model, is a
collection of RIBs, interfaces, and routing parameters. A routing
instance creates a logical slice of the router. It allows different
logical slices across a set of routers to communicate with each
other. Layer 3 Virtual Private Networks (VPN), Layer 2 VPNs (L2VPN)
and Virtual Private Lan Service (VPLS) can be modeled as routing
instances. Note that modeling a Layer 2 VPN using a routing instance
only models the Layer-3 (RIB) aspect and does not model any layer-2
information (like ARP) that might be associated with the L2VPN.
The set of interfaces indicates which interfaces are associated with
this routing instance. The RIBs specify how incoming traffic is to
be forwarded, and the routing parameters control the information in
the RIBs. The intersection set of interfaces of 2 routing instances
MUST be the null set. In other words, an interface MUST NOT be
present in 2 routing instances. Thus a routing instance describes
the routing information and parameters across a set of interfaces.
A routing instance MUST contain the following mandatory fields:
o INSTANCE_NAME: A routing instance is identified by its name,
INSTANCE_NAME. This MUST be unique across all routing instances
in a given network device.
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o rib-list: This is the list of RIBs associated with this routing
instance. Each routing instance can have multiple RIBs to
represent routes of different types. For example, one would put
IPv4 routes in one RIB and MPLS routes in another RIB. The list
of RIBs can be an empty list.
A routing instance MAY contain the following fields:
o interface-list: This represents the list of interfaces associated
with this routing instance. The interface list helps constrain
the boundaries of packet forwarding. Packets coming in on these
interfaces are directly associated with the given routing
instance. The interface list contains a list of identifiers, with
each identifier uniquely identifying an interface.
o ROUTER_ID: This field identifies the network device in control
plane interactions with other network devices. This field is to
be used if one wants to virtualize a physical router into multiple
virtual routers. Each virtual router MUST have a unique
ROUTER_ID. ROUTER_ID MUST be unique across all network devices in
a given domain.
A routing instance may be created purely for the purposes of packet
processing and may not have any interfaces associated with it. For
example, an incoming packet in routing instance A might have a
nexthop of routing instance B and after packet processing in B, the
nexthop might be routing instance C. Thus, routing instance B is not
associated with any interface. And given that this routing instance
does not do any control plane interaction with other network devices,
a ROUTER_ID is also not needed.
2.3. Route
A route is essentially a match condition and an action following the
match. The match condition specifies the kind of route (IPv4, MPLS,
etc.) and the set of fields to match on. Figure 3 represents the
overall contents of a route. Please note that for ease of depiction
in ASCII art only a single instance of the route attribute, match
flags, or nexthop is depicted.
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route
| | |
+---------+ | +----------+
| | |
0..N | | |
route-attribute match nexthop
|
|
+-------+-------+-------+--------+
| | | | |
| | | | |
IPv4 IPv6 MPLS MAC Interface
Figure 3: Route model
This document specifies the following match types:
o IPv4: Match on destination and/or source IP address in the IPv4
header
o IPv6: Match on destination and/or source IP address in the IPv6
header
o MPLS: Match on an MPLS label at the top of the MPLS label stack
o MAC: Match on MAC destination addresses in the Ethernet header
o Interface: Match on incoming interface of the packet
A route MAY be matched on one or more these match types by policy as
either an "AND" (to restrict the number of routes) or an "OR" (to
combine two filters).
Each route MUST have associated with it the following mandatory route
attributes:
o ROUTE_PREFERENCE: This is a numerical value that allows for
comparing routes from different protocols. Static configuration
is also considered a protocol for the purpose of this field. It
is also known as administrative-distance. The lower the value,
the higher the preference. For example there can be an OSPF route
for 192.0.2.1/32 (or IPv6 2001:DB8::1/128) with a preference of 5.
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If a controller programs a route for 192.0.2.1/32 (or IPv6 2001:
DB8::1/128) with a preference of 2, then the controller's route
will be preferred by the RIB manager. Preference should be used
to dictate behavior. For more examples of preference, see
Section 7.1.
Each route can have associated with it one or more optional route
attributes.
o route-vendor-attributes: Vendors can specify vendor-specific
attributes using this. The details of this attribute is outside
the scope of this document.
Each route has associated with it a nexthop. Nexthop is described in
Section 2.4.
Additional features to match multicast packets were considered (e.g.,
TTL of the packet to limit the range of a multicast group), but these
were not added to this information model. Future RIB information
models should investigate these multicast features.
2.4. Nexthop
A nexthop represents an object resulting from a route lookup. For
example, if a route lookup results in sending the packet out a given
interface, then the nexthop represents that interface.
Nexthops can be fully resolved nexthops or unresolved nexthop. A
resolved nexthop has adequate information to send the outgoing packet
to the destination by forwarding it on an interface to a directly
connected neighbor. For example, a nexthop to a point-to-point
interface or a nexthop to an IP address on an Ethernet interface has
the nexthop resolved. An unresolved nexthop is something that
requires the RIB manager to determine the final resolved nexthop.
For example, a nexthop could be an IP address. The RIB manager would
resolve how to reach that IP address, e.g., is the IP address
reachable by regular IP forwarding or by an MPLS tunnel or by both.
If the RIB manager cannot resolve the nexthop, then the nexthop
remains in an unresolved state and is NOT a candidate for
installation in the FIB. Future RIB events can cause an unresolved
nexthop to get resolved (e.g., IP address being advertised by an IGP
neighbor). Conversely, resolved nexthops can also become unresolved
(e.g., in the case of a tunnel going down) and hence would no longer
be candidates to be installed in the FIB.
When at least one of a route's nexthops is resolved, then the route
can be used to forward packets. Such a route is considered eligible
to be installed in the FIB and is henceforth referred to as a FIB-
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eligible route. Conversely, when all the nexthops of a route are
unresolved that route can no longer be used to forward packets. Such
a route is considered ineligible to be installed in the FIB and is
henceforth referred to as a FIB-ineligible route. The RIB
information model allows a RIB client to program routes whose
nexthops may be unresolved initially. Whenever an unresolved nexthop
gets resolved, the RIB manager will send a notification of the same
(see Section 5 ).
The overall structure and usage of a nexthop is as shown in the
figure below. For ease of ASCII art depiction, only a single
instance of any component of the nexthop is shown in Figure 4.
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route
|
| 0..N
|
nexthop <-------------------------------+
| |
+-------+----------------------------+-------------+ |
| | | | | |
| | | | | |
base load-balance protection replicate chain |
| | | | | |
| |2..N |2..N |2..N |1..N |
| | | | | |
| | V | | |
| +------------->+<------------+-------------+ |
| | |
| +-------------------------------------+
|
+-------------------+
|
|
|
|
+---------------+--------+--------+--------------+----------+
| | | | |
| | | | |
nexthop-id egress-interface ip-address logical-tunnel |
|
|
+--------------------------------------+
|
+--------------+----------+-------------+
| | | |
| | | |
tunnel-encap tunnel-decap rib-name special-nexthop
Figure 4: Nexthop model
This document specifies a very generic, extensible, and recursive
grammar for nexthops. A nexthop can be a base nexthop or a derived
nexthop. Section 2.4.1 details base nexthops and Section 2.4.2
explains various kinds of derived nexthops. There are certain
special nexthops and those are described in Section 2.4.1.1. Lastly,
Section 2.4.3 delves into nexthop indirection and it's use. Examples
of when and how to use tunnel nexthops and derived nexthops are shown
in Section 7.2.
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2.4.1. Base nexthop
At the lowest level, a nexthop can be one of:
o Identifier: This is an identifier returned by the network device
representing a nexthop. This can be used as a way of re-using a
nexthop when programming derived nexthops.
o Interface nexthops - nexthops pointing to an interface. Various
attributes associated with these nexthops are:
* EGRESS_INTERFACE: This represents a physical, logical, or
virtual interface on the network device. Address resolution
must not be required on this interface. This interface may
belong to any routing instance.
* IP address: A route lookup on this IP address is done to
determine the egress interface. Address resolution may be
required depending on the interface.
+ An optional RIB name can also be specified to indicate the
RIB in which the IP address is to be looked up. One can use
the RIB name field to direct the packet from one domain into
another domain. By default the RIB will be the same as the
one that route belongs to.
These attributes can be used in combination as follows:
* EGRESS_INTERFACE and IP address: This can be used in cases,
e.g., where the IP address is a link-local address.
* EGRESS_INTERFACE and MAC address: The egress interface must be
an Ethernet interface. Address resolution is not required for
this nexthop.
o Tunnel nexthops - nexthops pointing to a tunnel. The types of
tunnel nexthops are:
* tunnel-encap: This can be an encapsulation representing an IP
tunnel or MPLS tunnel or others as defined in this document.
An optional egress interface can be chained to the tunnel-encap
to indicate which interface to send the packet out on. The
egress interface is useful when the network device contains
Ethernet interfaces and one needs to perform address resolution
for the IP packet.
* tunnel-decap: This is to specify decapsulating a tunnel header.
After decapsulation, further lookup on the packet can be done
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via chaining it with another nexthop. The packet can also be
sent out via an EGRESS_INTERFACE directly.
* logical-tunnel: This can be an MPLS LSP or a GRE tunnel (or
others as defined in this document), that is represented by a
unique identifier (e.g., name).
o RIB_NAME: A nexthop pointing to a RIB. This indicates that the
route lookup needs to continue in the specified RIB. This is a
way to perform chained lookups.
Tunnel nexthops allow a RIB client to program static tunnel headers.
There can be cases where the remote tunnel endpoint does not support
dynamic signaling (e.g., no LDP support on a host) and in those cases
the RIB client might want to program the tunnel header on both ends
of the tunnel. The tunnel nexthop is kept generic with
specifications provided for some commonly used tunnels. It is
expected that the data-model will model these tunnel types with
complete accuracy.
2.4.1.1. Special nexthops
Special nexthops are for performing specific well-defined functions
(e.g., discard). The purpose of each of them is explained below:
o DISCARD: This indicates that the network device should drop the
packet and increment a drop counter.
o DISCARD_WITH_ERROR: This indicates that the network device should
drop the packet, increment a drop counter and send back an
appropriate error message (like ICMP error).
o RECEIVE: This indicates that that the traffic is destined for the
network device. For example, protocol packets or OAM packets.
All locally destined traffic SHOULD be throttled to avoid a denial
of service attack on the router's control plane. An optional
rate-limiter can be specified to indicate how to throttle traffic
destined for the control plane. The description of the rate-
limiter is outside the scope of this document.
2.4.2. Derived nexthops
Derived nexthops can be:
o Weighted lists - for load-balancing
o Preference lists - for protection using primary and backup
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o Replication lists - list of nexthops to which to replicate a
packet
o Nexthop chains - for chaining multiple operations or attaching
multiple headers
o Lists of lists - recursive application of the above
Nexthop chains (See Section 7.2.5 for usage) are a way to perform
multiple operations on a packet by logically combining them. For
example, one can chain together "decapsulate MPLS header" and "send
it out a specific EGRESS_INTERFACE". Chains can be used to specify
multiple headers over a packet before a packet is forwarded. One
simple example is that of MPLS over GRE, wherein the packet has an
inner MPLS header followed by a GRE header followed by an IP header.
The outermost IP header is decided by the network device whereas the
MPLS header or GRE header are specified by the controller. Not every
network device will be able to support all kinds of nexthop chains
and an arbitrary number of headers chained together. The RIB data-
model SHOULD provide a way to expose nexthop chaining capability
supported by a given network device.
It is expected that all network devices will have a limit on how many
levels of lookup can be performed and not all hardware will be able
to support all kinds of nexthops. RIB capability negotiation becomes
very important for this reason and a RIB data-model MUST specify a
way for a RIB client to learn about the network device's
capabilities.
2.4.2.1. Nexthop list attributes
For nexthops that are of the form of a list(s), attributes can be
associated with each member of the list to indicate the role of an
individual member of the list. Two attributes are specified:
o NEXTHOP_PREFERENCE: This is used for protection schemes. It is an
integer value between 1 and 99. A lower value indicates higher
preference. To download a primary/standby pair to the FIB, the
nexthops that are resolved and have the two highest preferences
are selected. Each <NEXTHOP_PREFERENCE> should have a unique
value within a <nexthop-protection> (Section 6).
o NEXTHOP_LB_WEIGHT: This is used for load-balancing. Each list
member MUST be assigned a weight between 1 and 99. The weight
determines the proportion of traffic to be sent over a nexthop
used for forwarding as a ratio of the weight of this nexthop
divided by the weights of all the nexthops of this route that are
used for forwarding. To perform equal load-balancing, one MAY
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specify a weight of "0" for all the member nexthops. The value
"0" is reserved for equal load-balancing and if applied, MUST be
applied to all member nexthops. Note: A weight of 0 is special
because of historical reasons.
2.4.3. Nexthop indirection
Nexthops can be identified by an identifier to create a level of
indirection. The identifier is set by the RIB manager and returned
to the RIB client on request.
One example of usage of indirection is a nexthop that points to
another network device (Eg. BGP peer). The returned nexthop
identifier can then be used for programming routes to point to the
this nexthop. Given that the RIB manager has created an indirection
using the nexthop identifier, if the transport path to the network
device (BGP peer) changes, that change in path will be seamless to
the RIB client and all routes that point to that network device will
automatically start going over the new transport path. Nexthop
indirection using identifiers could be applied to not just unicast
nexthops, but even to nexthops that contain chains and nested
nexthops. See (Section 2.4.2) for examples.
3. Reading from the RIB
A RIB data-model MUST allow a RIB client to read entries for RIBs
created by that entity. The network device administrator MAY allow
reading of other RIBs by a RIB client through access lists on the
network device. The details of access lists are outside the scope of
this document.
The data-model MUST support a full read of the RIB and subsequent
incremental reads of changes to the RIB. When sending data to a RIB
client, the RIB manager SHOULD try to send all dependencies of an
object prior to sending that object.
4. Writing to the RIB
A RIB data-model MUST allow a RIB client to write entries for RIBs
created by that entity. The network device administrator MAY allow
writes to other RIBs by a RIB client through access lists on the
network device. The details of access lists are outside the scope of
this document.
When writing an object to a RIB, the RIB client SHOULD try to write
all dependencies of the object prior to sending that object. The
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data-model SHOULD support requesting identifiers for nexthops and
collecting the identifiers back in the response.
Route programming in the RIB MUST result in a return code that
contains the following attributes:
o Installed - Yes/No (Indicates whether the route got installed in
the FIB)
o Active - Yes/No (Indicates whether a route is fully resolved and
is a candidate for selection)
o Reason - e.g., Not authorized
The data-model MUST specify which objects can be modified. An object
that can be modified is one whose contents can be changed without
having to change objects that depend on it and without affecting any
data forwarding. To change a non-modifiable object, one will need to
create a new object and delete the old one. For example, routes that
use a nexthop that is identified by a nexthop identifier should be
unaffected when the contents of that nexthop changes.
5. Notifications
Asynchronous notifications are sent by the network device's RIB
manager to a RIB client when some event occurs on the network device.
A RIB data-model MUST support sending asynchronous notifications. A
brief list of suggested notifications is as below:
o Route change notification, with return code as specified in
Section 4
o Nexthop resolution status (resolved/unresolved) notification
6. RIB grammar
This section specifies the RIB information model in Routing Backus-
Naur Form [RFC5511]. This grammar is intended to help the reader
better understand Section 2 in order to derive a data model.
<routing-instance> ::= <INSTANCE_NAME>
[<interface-list>] <rib-list>
[<ROUTER_ID>]
<interface-list> ::= (<INTERFACE_IDENTIFIER> ...)
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<rib-list> ::= (<rib> ...)
<rib> ::= <RIB_NAME> <address-family>
[<route> ... ]
[ENABLE_IP_RPF_CHECK]
<address-family> ::= <IPV4_ADDRESS_FAMILY> | <IPV6_ADDRESS_FAMILY> |
<MPLS_ADDRESS_FAMILY> | <IEEE_MAC_ADDRESS_FAMILY>
<route> ::= <match> <nexthop>
[<route-attributes>]
[<route-vendor-attributes>]
<match> ::= <IPV4> <ipv4-route> | <IPV6> <ipv6-route> |
<MPLS> <MPLS_LABEL> | <IEEE_MAC> <MAC_ADDRESS> |
<INTERFACE> <INTERFACE_IDENTIFIER>
<route-type> ::= <IPV4> | <IPV6> | <MPLS> | <IEEE_MAC> | <INTERFACE>
<ipv4-route> ::= <ip-route-type>
(<destination-ipv4-address> | <source-ipv4-address> |
(<destination-ipv4-address> <source-ipv4-address>))
<destination-ipv4-address> ::= <ipv4-prefix>
<source-ipv4-address> ::= <ipv4-prefix>
<ipv4-prefix> ::= <IPV4_ADDRESS> <IPV4_PREFIX_LENGTH>
<ipv6-route> ::= <ip-route-type>
(<destination-ipv6-address> | <source-ipv6-address> |
(<destination-ipv6-address> <source-ipv6-address>))
<destination-ipv6-address> ::= <ipv6-prefix>
<source-ipv6-address> ::= <ipv6-prefix>
<ipv6-prefix> ::= <IPV6_ADDRESS> <IPV6_PREFIX_LENGTH>
<ip-route-type> ::= <SRC> | <DEST> | <DEST_SRC>
<route-attributes> ::= <ROUTE_PREFERENCE> [<LOCAL_ONLY>]
[<address-family-route-attributes>]
<address-family-route-attributes> ::= <ip-route-attributes> |
<mpls-route-attributes> |
<ethernet-route-attributes>
<ip-route-attributes> ::= <>
<mpls-route-attributes> ::= <>
<ethernet-route-attributes> ::= <>
<route-vendor-attributes> ::= <>
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<nexthop> ::= <nexthop-base> |
(<NEXTHOP_LOAD_BALANCE> <nexthop-lb>) |
(<NEXTHOP_PROTECTION> <nexthop-protection>) |
(<NEXTHOP_REPLICATE> <nexthop-replicate>) |
<nexthop-chain>
<nexthop-base> ::= <NEXTHOP_ID> |
<nexthop-special> |
<EGRESS_INTERFACE> |
<ipv4-address> | <ipv6-address> |
(<EGRESS_INTERFACE>
(<ipv4-address> | <ipv6-address>)) |
(<EGRESS_INTERFACE> <IEEE_MAC_ADDRESS>) |
<tunnel-encap> | <tunnel-decap> |
<logical-tunnel> |
<RIB_NAME>)
<EGRESS_INTERFACE> ::= <INTERFACE_IDENTIFIER>
<nexthop-special> ::= <DISCARD> | <DISCARD_WITH_ERROR> |
(<RECEIVE> [<COS_VALUE>])
<nexthop-lb> ::= <NEXTHOP_LB_WEIGHT> <nexthop>
(<NEXTHOP_LB_WEIGHT> <nexthop) ...
<nexthop-protection> = <NEXTHOP_PREFERENCE> <nexthop>
(<NEXTHOP_PREFERENCE> <nexthop>)...
<nexthop-replicate> ::= <nexthop> <nexthop> ...
<nexthop-chain> ::= <nexthop> ...
<logical-tunnel> ::= <tunnel-type> <TUNNEL_NAME>
<tunnel-type> ::= <IPV4> | <IPV6> | <MPLS> | <GRE> | <VxLAN> | <NVGRE>
<tunnel-encap> ::= (<IPV4> <ipv4-header>) |
(<IPV6> <ipv6-header>) |
(<MPLS> <mpls-header>) |
(<GRE> <gre-header>) |
(<VXLAN> <vxlan-header>) |
(<NVGRE> <nvgre-header>)
<ipv4-header> ::= <SOURCE_IPv4_ADDRESS> <DESTINATION_IPv4_ADDRESS>
<PROTOCOL> [<TTL>] [<DSCP>]
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<ipv6-header> ::= <SOURCE_IPV6_ADDRESS> <DESTINATION_IPV6_ADDRESS>
<NEXT_HEADER> [<TRAFFIC_CLASS>]
[<FLOW_LABEL>] [<HOP_LIMIT>]
<mpls-header> ::= (<mpls-label-operation> ...)
<mpls-label-operation> ::= (<MPLS_PUSH> <MPLS_LABEL> [<S_BIT>]
[<TOS_VALUE>] [<TTL_VALUE>]) |
(<MPLS_SWAP> <IN_LABEL> <OUT_LABEL>
[<TTL_ACTION>])
<gre-header> ::= <GRE_IP_DESTINATION> <GRE_PROTOCOL_TYPE> [<GRE_KEY>]
<vxlan-header> ::= (<ipv4-header> | <ipv6-header>)
[<VXLAN_IDENTIFIER>]
<nvgre-header> ::= (<ipv4-header> | <ipv6-header>)
<VIRTUAL_SUBNET_ID>
[<FLOW_ID>]
<tunnel-decap> ::= ((<IPV4> <IPV4_DECAP> [<TTL_ACTION>]) |
(<IPV6> <IPV6_DECAP> [<HOP_LIMIT_ACTION>]) |
(<MPLS> <MPLS_POP> [<TTL_ACTION>]))
Figure 5: RIB rBNF grammar
6.1. Nexthop grammar explained
A nexthop is used to specify the next network element to forward the
traffic to. It is also used to specify how the traffic should be
load-balanced, protected using preference, or multicast using
replication. This is explicitly specified in the grammar. The
nexthop has recursion built-in to address complex use cases like the
one defined in Section 7.2.6.
7. Using the RIB grammar
The RIB grammar is very generic and covers a variety of features.
This section provides examples on using objects in the RIB grammar
and examples to program certain use cases.
7.1. Using route preference
Using route preference a client can pre-install alternate paths in
the network. For example, if OSPF has a route preference of 10, then
another client can install a route with route preference of 20 to the
same destination. The OSPF route will get precedence and will get
installed in the FIB. When the OSPF route is withdrawn, the
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alternate path will get installed in the FIB.
Route preference can also be used to prevent denial of service
attacks by installing routes with the best preference, which either
drops the offending traffic or routes it to some monitoring/analysis
station. Since the routes are installed with the best preference,
they will supersede any route installed by any other protocol.
7.2. Using different nexthops types
The RIB grammar allows one to create a variety of nexthops. This
section describes uses for certain types of nexthops.
7.2.1. Tunnel nexthops
A tunnel nexthop points to a tunnel of some kind. Traffic that goes
over the tunnel gets encapsulated with the tunnel-encap. Tunnel
nexthops are useful for abstracting out details of the network, by
having the traffic seamlessly route between network edges. At the
end of a tunnel, the tunnel will get decapsulated. Thus the grammar
supports two kinds of operations, one for encapsulation and another
for decapsulation.
7.2.2. Replication lists
One can create a replication list for replicating traffic to multiple
destinations. The destinations, in turn, could be derived nexthops
in themselves - at a level supported by the network device. Point to
multipoint and broadcast are examples that involve replication.
A replication list (at the simplest level) can be represented as:
<nexthop> ::= <NEXTHOP_REPLICATE> <nexthop> [ <nexthop> ... ]
The above can be derived from the grammar as follows:
<nexthop> ::= <nexthop-replicate>
<nexthop> ::= <NEXTHOP_REPLICATE> <nexthop> <nexthop> ...
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7.2.3. Weighted lists
A weighted list is used to load-balance traffic among a set of
nexthops. From a modeling perspective, a weighted list is very
similar to a replication list, with the difference that each member
nexthop MUST have a NEXTHOP_LB_WEIGHT associated with it.
A weighted list (at the simplest level) can be represented as:
<nexthop> ::= <NEXTHOP_LOAD_BALANCE> (<nexthop> <NEXTHOP_LB_WEIGHT>)
[(<nexthop> <NEXTHOP_LB_WEIGHT>)... ]
The above can be derived from the grammar as follows:
<nexthop> ::= <nexthop-lb>
<nexthop> ::= <NEXTHOP_LOAD_BALANCE>
<NEXTHOP_LB_WEIGHT> <nexthop>
(<NEXTHOP_LB_WEIGHT> <nexthop>) ...
<nexthop> ::= <NEXTHOP_LOAD_BALANCE> (<NEXTHOP_LB_WEIGHT> <nexthop>)
(<NEXTHOP_LB_WEIGHT> <nexthop>) ...
7.2.4. Protection
A primary/backup protection can be represented as:
<nexthop> ::= <NEXTHOP_PROTECTION> <1> <interface-primary>
<2> <interface-backup>)
The above can be derived from the grammar as follows:
<nexthop> ::= <nexthop-protection>
<nexthop> ::= <NEXTHOP_PROTECTION> (<NEXTHOP_PREFERENCE> <nexthop>
(<NEXTHOP_PREFERENCE> <nexthop>)...)
<nexthop> ::= <NEXTHOP_PROTECTION> (<NEXTHOP_PREFERENCE> <nexthop>
(<NEXTHOP_PREFERENCE> <nexthop>))
<nexthop> ::= <NEXTHOP_PROTECTION> ((<NEXTHOP_PREFERENCE> <nexthop-base>
(<NEXTHOP_PREFERENCE> <nexthop-base>))
<nexthop> ::= <NEXTHOP_PROTECTION> (<1> <interface-primary>
(<2> <interface-backup>))
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Traffic can be load-balanced among multiple primary nexthops and a
single backup. In such a case, the nexthop will look like:
<nexthop> ::= <NEXTHOP_PROTECTION> (<1>
(<NEXTHOP_LOAD_BALANCE>
(<NEXTHOP_LB_WEIGHT> <nexthop-base>
(<NEXTHOP_LB_WEIGHT> <nexthop-base>) ...))
<2> <nexthop-base>)
A backup can also have another backup. In such a case, the list will
look like:
<nexthop> ::= <NEXTHOP_PROTECTION> (<1> <nexthop>
<2> <NEXTHOP_PROTECTION>(<1> <nexthop> <2> <nexthop>))
7.2.5. Nexthop chains
A nexthop chain is a way to perform multiple operations on a packet
by logically combining them. For example, when a VPN packet comes on
the WAN interface and has to be forwarded to the correct VPN
interface, one needs to POP the VPN label before sending the packet
out. Using a nexthop chain, one can chain together "pop MPLS header"
and "send it out a specific EGRESS_INTERFACE".
The above example can be derived from the grammar as follows:
<nexthop-chain> ::= <nexthop> <nexthop>
<nexthop-chain> ::= <nexthop-base> <nexthop-base>
<nexthop-chain> ::= <tunnel-decap> <EGRESS_INTERFACE>
<nexthop-chain> ::= (<MPLS> <MPLS_POP>) <interface-outgoing>
Elements in a nexthop-chain are evaluated left to right.
A nexthop chain can also be used to put one or more headers on an
outgoing packet. One example is a Pseudowire - which is MPLS over
some transport (MPLS or GRE for instance). Another example is VxLAN
over IP. A nexthop chain thus allows a RIB client to break up the
programming of the nexthop into independent pieces - one per
encapsulation.
A simple example of MPLS over GRE can be represented as:
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<nexthop-chain> ::= (<MPLS> <mpls-header>) (<GRE> <gre-header>)
<interface-outgoing>
The above can be derived from the grammar as follows:
<nexthop-chain> ::= <nexthop> <nexthop> <nexthop>
<nexthop-chain> ::= <nexthop-base> <nexthop-base> <nexthop-base>
<nexthop-chain> ::= <tunnel-encap> <tunnel-encap> <EGRESS_INTERFACE>
<nexthop-chain> ::= (<MPLS> <mpls-header>) (<GRE> <gre-header>)
<interface-outgoing>
7.2.6. Lists of lists
Lists of lists is a derived construct. One example of usage of such
a construct is to replicate traffic to multiple destinations, with
load balancing. In other words for each branch of the replication
tree, there are multiple interfaces on which traffic needs to be
load-balanced on. So the outer list is a replication list for
multicast and the inner lists are weighted lists for load balancing.
Let's take an example of a network element has to replicate traffic
to two other network elements. Traffic to the first network element
should be load balanced equally over two interfaces outgoing-1-1 and
outgoing-1-2. Traffic to the second network element should be load
balanced over three interfaces outgoing-2-1, outgoing-2-2 and
outgoing-2-3 in the ratio 20:20:60.
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This can be derived from the grammar as follows:
<nexthop> ::= <nexthop-replicate>
<nexthop> ::= <NEXTHOP_REPLICATE> (<nexthop> <nexthop>...)
<nexthop> ::= <NEXTHOP_REPLICATE> (<nexthop> <nexthop>)
<nexthop> ::= <NEXTHOP_REPLICATE> ((<NEXTHOP_LOAD_BALANCE> <nexthop-lb>)
(<NEXTHOP_LOAD_BALANCE> <nexthop-lb>))
<nexthop> ::= <NEXTHOP_REPLICATE> ((<NEXTHOP_LOAD_BALANCE>
(<NEXTHOP_LB_WEIGHT> <nexthop>
(<NEXTHOP_LB_WEIGHT> <nexthop>) ...))
((<NEXTHOP_LOAD_BALANCE>
(<NEXTHOP_LB_WEIGHT> <nexthop>
(<NEXTHOP_LB_WEIGHT> <nexthop>) ...))
<nexthop> ::= <NEXTHOP_REPLICATE> ((<NEXTHOP_LOAD_BALANCE>
(<NEXTHOP_LB_WEIGHT> <nexthop>
(<NEXTHOP_LB_WEIGHT> <nexthop>)))
((<NEXTHOP_LOAD_BALANCE>
(<NEXTHOP_LB_WEIGHT> <nexthop>
(<NEXTHOP_LB_WEIGHT> <nexthop>)
(<NEXTHOP_LB_WEIGHT> <nexthop>)))
<nexthop> ::= <NEXTHOP_REPLICATE> ((<NEXTHOP_LOAD_BALANCE>
(<NEXTHOP_LB_WEIGHT> <nexthop>)
(<NEXTHOP_LB_WEIGHT> <nexthop>)))
((<NEXTHOP_LOAD_BALANCE>
(<NEXTHOP_LB_WEIGHT> <nexthop>)
(<NEXTHOP_LB_WEIGHT> <nexthop>)
(<NEXTHOP_LB_WEIGHT> <nexthop>)))
<nexthop> ::= <NEXTHOP_REPLICATE>
((<NEXTHOP_LOAD_BALANCE>
(50 <outgoing-1-1>)
(50 <outgoing-1-2>)))
((<NEXTHOP_LOAD_BALANCE>
(20 <outgoing-2-1>)
(20 <outgoing-2-2>)
(60 <outgoing-2-3>)))
7.3. Performing multicast
IP multicast involves matching a packet on (S, G) or (*, G), where
both S (source) and G (group) are IP prefixes. Following the match,
the packet is replicated to one or more recipients. How the
recipients subscribe to the multicast group is outside the scope of
this document.
In PIM-based multicast, the packets are IP forwarded on an IP
multicast tree. The downstream nodes on each point in the multicast
tree is one or more IP addresses. These can be represented as a
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replication list ( Section 7.2.2 ).
In MPLS-based multicast, the packets are forwarded on a point to
multipoint (P2MP) label-switched path (LSP). The nexthop for a P2MP
LSP can be represented in the nexthop grammar as a <logical-tunnel>
(P2MP LSP identifier) or a replication list ( Section 7.2.2) of
<tunnel-encap>, with each tunnel encap representing a single mpls
downstream nexthop.
8. RIB operations at scale
This section discusses the scale requirements for a RIB data-model.
The RIB data-model should be able to handle large scale of operations
to enable deployment of RIB applications in large networks.
8.1. RIB reads
Bulking (grouping of multiple objects in a single message) MUST be
supported when a network device sends RIB data to a RIB client.
Similarly the data model MUST enable a RIB client to request data in
bulk from a network device.
8.2. RIB writes
Bulking (grouping of multiple write operations in a single message)
MUST be supported when a RIB client wants to write to the RIB. The
response from the network device MUST include a return-code for each
write operation in the bulk message.
8.3. RIB events and notifications
There can be cases where a single network event results in multiple
events and/or notifications from the network device to a RIB client.
On the other hand, due to timing of multiple things happening at the
same time, a network device might have to send multiple events and/or
notifications to a RIB client. The network device originated event/
notification message MUST support bulking of multiple events and
notifications in a single message.
9. Security Considerations
The Informational module specified in this document defines a schema
for data models that are designed to be accessed via network
management protocols such as NETCONF [RFC6241] or RESTCONF [RFC8040].
The lowest NETCONF layer is the secure transport layer, and the
mandatory-to-implement secure transport is Secure Shell (SSH)
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[RFC6242]. The lowest RESTCONF layer is HTTPS, and the mandatory-to-
implement secure transport is TLS [RFC5246].
The NETCONF access control model [RFC8341] provides the means to
restrict access for particular NETCONF or RESTCONF users to a
preconfigured subset of all available NETCONF or RESTCONF protocol
operations and content.
The RIB info model specifies read and write operations to network
devices. These network devices might be considered sensitive or
vulnerable in some network environments. Write operations to these
network devices without proper protection can have a negative effect
on network operations. Due to this factor, it is recommended that
data models also consider the following in their design:
o Require utilization of the authentication and authorization
features of the NETCONF or RESTCONF suite of protocols.
o Augment the limits on how much data can be written or updated by a
remote entity built to include enough protection for a RIB model.
o Expose the specific RIB model implemented via NETCONF/RESTCONF
data models.
10. IANA Considerations
This document does not generate any considerations for IANA.
11. Acknowledgements
The authors would like to thank Ron Folkes, Jeffrey Zhang, the
working group co-chairs, and reviewers for their comments and
suggestions on this draft. The following people contributed to the
design of the RIB model as part of the I2RS Interim meeting in April
2013 - Wes George, Chris Liljenstolpe, Jeff Tantsura, Susan Hares,
and Fabian Schneider.
12. References
12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
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[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
12.2. Informative References
[I-D.ietf-i2rs-rib-data-model]
Wang, L., Chen, M., Dass, A., Ananthakrishnan, H., Kini,
S., and N. Bahadur, "A YANG Data Model for Routing
Information Base (RIB)", draft-ietf-i2rs-rib-data-model-14
(work in progress), May 2018.
[RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P.
Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF",
RFC 4915, DOI 10.17487/RFC4915, June 2007,
<https://www.rfc-editor.org/info/rfc4915>.
[RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
Topology (MT) Routing in Intermediate System to
Intermediate Systems (IS-ISs)", RFC 5120, DOI 10.17487/
RFC5120, February 2008,
<https://www.rfc-editor.org/info/rfc5120>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, DOI 10.17487/
RFC5246, August 2008,
<https://www.rfc-editor.org/info/rfc5246>.
[RFC5511] Farrel, A., "Routing Backus-Naur Form (RBNF): A Syntax
Used to Form Encoding Rules in Various Routing Protocol
Specifications", RFC 5511, DOI 10.17487/RFC5511,
April 2009, <https://www.rfc-editor.org/info/rfc5511>.
[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
and A. Bierman, Ed., "Network Configuration Protocol
(NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
<https://www.rfc-editor.org/info/rfc6241>.
[RFC6242] Wasserman, M., "Using the NETCONF Protocol over Secure
Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011,
<https://www.rfc-editor.org/info/rfc6242>.
[RFC7920] Atlas, A., Ed., Nadeau, T., Ed., and D. Ward, "Problem
Statement for the Interface to the Routing System",
RFC 7920, DOI 10.17487/RFC7920, June 2016,
<https://www.rfc-editor.org/info/rfc7920>.
[RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
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Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
<https://www.rfc-editor.org/info/rfc8040>.
[RFC8341] Bierman, A. and M. Bjorklund, "Network Configuration
Access Control Model", STD 91, RFC 8341, DOI 10.17487/
RFC8341, March 2018,
<https://www.rfc-editor.org/info/rfc8341>.
Authors' Addresses
Nitin Bahadur (editor)
Uber
900 Arastradero Rd
Palo Alto, CA 94304
US
Email: nitin_bahadur@yahoo.com
Sriganesh Kini (editor)
Email: sriganeshkini@gmail.com
Jan Medved
Cisco
Email: jmedved@cisco.com
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