wdiff draft-ietf-babel-source-specific-00.txt draft-ietf-babel-source-specific-01.txt

Network Working Group M. Boutier
Internet-Draft J. Chroboczek
Updates: 6126bis (if approved) IRIF, University of Paris-Diderot
(if approved) August 11, 2017
Intended status: Standards Track August 21, 2017
Expires: February 12, 22, 2018

Source-Specific Routing in Babel
draft-ietf-babel-source-specific-00
draft-ietf-babel-source-specific-01

Abstract

Source-specific routing is an extension to traditional next-hop
routing where packets are forwarded according to both their
destination and their source address. This document describes an the
source-specific routing extension to the Standard Track's Babel
routing protocol to
support source-specific routing. defined in [BABEL]. It is incompatible with the
Experimental Track's Babel [RFC6126].

Source-specific routing is also known as Source Address Dependent
Routing, SAD Routing, SADR, Destination/Source Routing or Source/
Destination Routing.

Status of this This Memo

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Table of Contents

1. TODOs . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2
2. Introduction and background . . . . . . . . . . . . . . . . . 3 2
3. Data Structures . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. The Source Table . . . . . . . . . . . . . . . . . . . . . 3
3.2. The Route Table . . . . . . . . . . . . . . . . . . . . . 3 4
3.3. The Table of Pending Seqno Requests . . . . . . . . . . . . . . 4
4. Data Forwarding . . . . . . . . . . . . . . . . . . . . . . . 4
5. Protocol Operation . . . . . . . . . . . . . . . . . . . . . . 5
5.1. Source-specific messages . . . . . . . . . . . . . . . . . 5 6
5.2. Route Acquisition . . . . . . . . . . . . . . . . . . . . 5 6
5.3. Wildcard retractions (update) . . . . . . . . . . . . . . 6
5.4. Wildcard requests . . . . . . . . . . . . . . . . . . . . 6
6. Compatibility with the base protocol . . . . . . . . . . . . . 8 7
6.1. Loop-avoidance . . . . . . . . . . . . . . . . . . . . . . 8 7
6.2. Starvation and Blackholes . . . . . . . . . . . . . . . . 9 8
7. Protocol Encoding . . . . . . . . . . . . . . . . . . . . . . 9 8
7.1. Source Prefix sub-TLV . . . . . . . . . . . . . . . . . . 9 8
7.2. Source-specific Update . . . . . . . . . . . . . . . . . . 10 9
7.3. Source-specific (Route) Request . . . . . . . . . . . . . 10 9
7.4. Source-Specific Seqno Request . . . . . . . . . . . . . . 10 9
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 9
9. Security considerations . . . . . . . . . . . . . . . . . . . 11 9
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 10
10.1. Normative References . . . . . . . . . . . . . . . . . . . 11 10
10.2. Informative References . . . . . . . . . . . . . . . . . . 11 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11 10

1. TODOs

o Source Prefix sub-TLV type: TBD

o check references (Section) for BABEL in 6126bis
o define wildcard Requests behaviour

2. Introduction and background

Source-specific

The Babel routing (also known protocol as Source Address Dependant
Routing, SAD Routing or SADR) defined is an extension to traditional next-hop [BABEL] is a distance vector
routing where packets are routed according protocol for next-hop routing. In next-hop routing, each
node maintains a forwarding table which maps prefixes to both their next-hops.
The forwarding decision is a per-packet operation which depends on
the destination address of the packets and their source address. This document describes on the source-
specific routing extension to entries of the Babel routing protocol as defined
in 6126bis [BABEL].

Background information
forwarding table. When a packet is about source-specific routing to be routed, its
destination address is provided in
[SS-ROUTING].

3. Data Structures

This extension adds some data compared to the data structures maintained by a
Babel node.

3.1. The Source Table

Every Babel node maintains a source table, as described in [BABEL],
Section 3.2.5. A source-specific Babel node extends this table with prefixes of the following field:

o routing table:
the source entry with the most specific prefix (sprefix, splen) specifying containing the source destination
address of packets to which this entry applies.

If a source table entry has a zero length source prefix (splen equals
to 0), then the entry packet is a non-source-specific entry, choosen, and is treated
just like a source table entry defined by the original Babel
protocol.

With this extension packet is forwarded to the route entry contains a source which itself
contains a source prefix. These are two very different concepts, and
should not be confused.

3.2. The Route Table

Every Babel node maintains
associated next-hop. Next-hop routing is a route table, as described simple, well understood
paradigm that works satisfactorily in [BABEL],
Section 3.2.6. With this extension, this table a large number of cases.

Source-specific routing is indexed by a modest extension of next-hop routing
where the
5-tuple (prefix, plen, source prefix, source plen, router-id)
obtained from forwarding decision additionnaly depends on the associated source table entry.

If
address of the packets. The forwarding tables are extended to map
pairs of prefixes (destination, source) to a next-hop. When multiple
entries are candidate to route table entry has a zero length source prefix, then packet, the
entry one with the most
specific destination prefix is a non-source-specific entry, choosen, and is treated just like a
route table entry defined by the original Babel protocol.

3.3. The Table of Pending Requests

Every Babel node maintains a table of pending requests, as described in [BABEL], Section 3.2.7. A source-specific Babel node extends this
table with case of equality the following entry:

o
one with the source prefix being requested.

4. Data Forwarding most specific source. In next-hop source-specific routing, if two
packets with the same destination but different sources may be
forwarded among different paths.

The main application of source-specific routing table entries overlap, then one
is necessarily more specific than is, at the other; time of
this writing, multihoming with Provider Agregatable (PA) addresses.
In such configuration, each Internet Service Provider (ISP) provides
to the "longest network a PA prefix
rule" specifies that the most specific applicable routing table entry
is chosen.

With source-specific routing, there might no longer be a most
specific applicable prefix: two routing table entries might match and a
given packet without one necessarily being more specific than the
other. Consider default route for example the following fragment this prefix while
performing ingress filtering ([BCP84]). Each host has one address
per ISP, and sends packets with one of a these addresses as source
address. Source-specific routing
table:

(2001:DB8:0:1::/64, ::/0, A)
(::/0, 2001:DB8:0:2::/64, B)

This specifies ensures that all packets with destination in 2001:DB8:0:1::/64 are to be routed through A, while packets with a
towards the provider of their source in 2001:DB8:
0:2::/64 address, such that they are to be routed through B. A packet with source 2001:DB8:0:
2::42 not
filtered out. More details and destination 2001:DB8:0:1::57 matches both rules, although
neither is more specific than use cases can be found in
[SS-ROUTING],[IETF-SSR].

This document describes the other. A choice is necessary, and
unless source-specific routing extension for the choice being made
Babel routing protocol [BABEL]. This involves changes to data
structures and protocol messages. The data structures receive an
additionnal source prefix which is part of the same on all routers in index, similarly to
(and with) the destination prefix. The Update, Route Request and
Seqno Request are the three messages which carry a routing
domain, persistent routing loops may occur. More informations (destination)
prefix: they are
available in [SS-ROUTING] Section IV.C.

A Babel implementation MUST choose routing table entries by using extended with a source prefix.

3. Data Structures

Some of the
so-called destination-first ordering, where data structures of a routing table entry R1
is preferred to Babel node contains a routing table entry R2 when either R1's destination
prefix is more specific than R2's, or the destination prefixes are
equal and R1's partly indexed by a destination prefix. This extension
adds a source prefix is more specific to these structures and indexes.

3.1. The Source Table

Every Babel node maintains a source table, as described in [BABEL],
Section 3.2.5. A source-specific Babel node extends this table with
the following field. With this extension, the source table is
indexed by triples of the form (prefix, source prefix, router-id).

o the source prefix specifying the source address of packets to
which this entry applies.

If a source table entry has a zero length source prefix, then the
entry is a non-source-specific entry, and is treated just like a
source table entry defined by the original Babel protocol.

With this extension, the route entry contains a source which itself
contains a source prefix. These are two very different concepts, and
should not be confused.

3.2. The Route Table

Every Babel node maintains a route table, as described in [BABEL],
Section 3.2.6. With this extension, the route table is indexed by
triples of the form (prefix, source prefix, neighbour) obtained from
the associated source table entry.

If a route table entry has a zero length source prefix, then the
entry is a non-source-specific entry, and is treated just like a
route table entry defined by the original Babel protocol.

3.3. The Table of Pending Seqno Requests

Every Babel node maintains a table of pending seqno requests, as
described in [BABEL], Section 3.2.7. A source-specific Babel node
extends this table with the following entry. With this extension,
the table of pending seqno requests is indexed by triples of the form
(prefix, source prefix, router-id).

o the source prefix being requested.

4. Data Forwarding

In next-hop routing, if two routing table entries overlap, then one
is necessarily more specific than the other; the "longest prefix
rule" specifies that the most specific applicable routing table entry
is chosen.

With source-specific routing, there might no longer be a most
specific applicable entry: two routing table entries might match a
given packet without one necessarily being more specific than the
other. Consider for example the following routing table:

destination source next-hop
2001:DB8:0:1::/64 ::/0 A
::/0 2001:DB8:0:2::/64 B

This specifies that all packets with destination in 2001:DB8:0:1::/64
are to be routed through A, while all packets with source in
2001:DB8:0:2::/64 are to be routed through B. A packet with source
2001:DB8:0:2::42 and destination 2001:DB8:0:1::57 matches both rules,
although neither is more specific than the other. A choice is
necessary, and unless the choice being made is the same on all
routers in a routing domain, persistent routing loops may occur.
More informations are available in [SS-ROUTING] Section IV.C.

A Babel implementation MUST choose routing table entries by using the
so-called destination-first ordering, where a routing table entry R1
is preferred to a routing table entry R2 when either R1's destination
prefix is more specific than R2's, or the destination prefixes are
equal and R1's source prefix is more specific than R2's. (In more
formal terms, routing table entries are compared using the
lexicographic product of the destination prefix ordering by the
source prefix ordering.)

In practice, this means that a source-specific Babel implementation
must take care that any lower layer that performs packet forwarding
obey this semantics. In particular:

o If the lower layers implement the destination-first ordering, then
the Babel implementation MAY use them directly;

o If the lower layers can hold source-specific routes, but not with
the right semantics, then the Babel implementation MUST
disambiguate the routing table by using a suitable disambiguation
algorithm (see [SS-ROUTING] Section V.B for such an algorithm);

o If the lower layers cannot hold source-specific routes, then a
Babel implementation MUST silently ignore (drop) any source-
specific routes.

5. Protocol Operation

This extension does not fundamentally change the operation of the
Babel protocol. We only describe the fundamental differences between
the original protocol and the this extension in this section. The other
mechanisms described in [BABEL] (Section 3) are extended to pairs of
(destination, source) prefixes instead of just (destination)
prefixes.

5.1. Source-specific messages

Three messages are used to communicate informations on routes: carry a destination prefix: Updates, Route Requests
and Seqno Requests. With this extension,
these These messages carry an additionnal are extended to carry, in
addition, a source prefix if (and only if) the corresponding route is
source-specific. More formally, an Update, a Route Request and a
Seqno Request MUST carry a source prefix if they concern a source-specific source-
specific route (non-zero length source prefix) and MUST NOT carry a
source prefix otherwise (zero length source prefix). A message which
carries a source prefix is said to be source-specific.

5.2. Route Acquisition

When a non-source-specific Babel node receives a source-specific
update, it silently ignores it.

TODO{On receipt of When a source-specific Babel node
receives a non-source-specific update, it MUST treat this update (id, prefix, source
prefix, seqno, metric), as a
zero length source-specific update.

When a source-specific Babel node receives a source-specific update
(prefix, source prefix, router-id, seqno, metric) from a neighbour
neigh, it behaves as described in [BABEL] Section 3.5.4 (Section 3.5.4) though
indexing entries by (neigh,
id, prefix, source prefix).} When a source-specific Babel node
receives a non-source-specific update, it MUST treat this update as
carrying a zero length (prefix, source prefix. prefix, neigh).

5.3. Wildcard retractions (update)

The original protocol defines a wildcard update with AE equals to 0
as being a wildcard retraction. A node receiving a wildcard
retraction on an interface must consider that the sending node
retracts all the routes it advertised on this interface.

Wildcard retractions are used when a node is about to leave the
network. Thus, this extension does not define source-specific
wildcard retraction, but extends wildcard retraction to apply also to
source-specific routes. More formally, a wildcard update MUST NOT
carry a source prefix, and a source-specific Babel node receiving a
(legacy) wildcard update MUST retracts all routes it learns from this
node (including source-specific ones).

5.4. Wildcard requests

TODO: behaviour to be defined.

5.4.1. Proposal 1

The original Babel protocol states that when a node receives a
wildcard route request, it SHOULD send a full routing table dump.
This extension does not change this statement: a source-specific node
SHOULD send a full routing table dump when receiving a wildcard
request.

Source-specific wildcard requests does not exist: a wildcard request
SHOULD NOT carry a source prefix.

5.4.2. Proposal 2

We assume that a mandatory sub-TLV has a corresponding non-mandatory
sub-TLV. This proposal is like Proposal 3 but instead of having
multiple wildcard request TLVs, one for each kind of route
understood, we use one wildcard request with sub-TLVs corresponding
to the extension. To have a full routing table dump, a node sends a
wildcard requests with a non-mandatory Source sub-TLV.

A source-specific node SHOULD always attach a non-mandatory Source
sub-TLV to its wildcard requests.

This proposal has been rejected because it implies to share the space
of non-mandatory and mandatory sub-TLVs.

5.4.3. Proposal 3 (mentionned by Juliusz)

The Babel protocol provides the ability to request a full routing
table dump by sending a "wildcard request", a route request with the
AE field set to 0. As the original protocol has no source-specific
routes, such a request may only concern non-source-specific routes.
This extension does not modify the semantics of wildcard requests in
that sense: a wildcard request prompts the receiver wildcard retraction to apply also to send its non-
source-specific routes only, and routes. More formally, a Babel node SHOULD wildcard update MUST NOT send any
source-specific updates in reply to
carry a wildcard request.

To obtain source prefix, and a dump of the source-specific routes, Babel node receiving a source-specific
(legacy) wildcard request update MUST be used. A retracts all routes it learns from this
node (including source-specific wildcard request is
a wildcard request carrying a zero length source prefix.

When ones).

5.4. Wildcard requests

The original Babel protocol states that when a node receives a source-specific
wildcard route request, it SHOULD send a dump of its routes which are source-specific "only". It
SHOULD NOT send any non-source-specific routes in reply to a source-
specific wildcard request. It SHOULD NOT send any source-specific
routes which are under the effect of a future extension. Such
extension should detail how to handle the possible combinations.

In consequence, a node requiring a full routing table dump must send
both a non-source-specific wildcard request and a source-specific
wildcard request.

5.4.4. Proposal 4 (mentionned by Juliusz)

Wildcard requests are deprecated. Either deprecate it in 6126bis, or
say the following.

A node receiving a wildcard request SHOULD ignore it.

This proposal has been rejected because wildcard requests speeds up
the convergence of the network on boot. This is considered
important.

5.4.5. Proposal 5 (mentionned by David)

By default, a vanilla wildcard request triggers a dump of all non-
specific routes. We define a new non-mandatory sub-TLV on Route
Requests called "Requested Route Types" that contains an array of all
the types of routes this request is requesting.

0 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 = TBD | Length | RR Type 1 | RR Type 2...

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

We also create a registry of Requested Route (RR) types, for example:

0 = Regular
1 = Source-Specific
2 = TOS-specific
etc.

A dump.
This extension does not change this statement: a source-specific node
SHOULD send a full routing table dump when receiving a Requested Route Types sub-TLV in wildcard
request.

Source-specific wildcard requests does not exist: a wildcard request SHOULD sends back
MUST NOT carry a dump source prefix, and a source prefix associated with a
wildcard update SHOULD be ignored.

One of all its routes corresponding the motivation behalf this design choice is that wildcard
requests are defined with AE equals to 0. They naturally apply to AE
1, AE 2 and AE 3 defined in [BABEL], but also to any other AE which
may be defined in the requested types future. New AEs, new TLVs or to a combination new sub-TLVs are
extension mechanisms. Thus, the semantics of these types. a wildcard request is
clearly to also asks for routes coming from extensions.

6. Compatibility with the base protocol

The protocol extension defined in this document is, to a great
extent, interoperable with the base protocol defined in [BABEL] (and
all its known extensions). More precisely, if non-source-specific
routers and source-specific routers are mixed in a single routing
domain, Babel's loop-avoidance properties are preserved, and, in
particular, no persistent routing loops will occur.

However, this extension is not compatible with the Experimental
Track's Babel Routing Protocol (RFC 6126). [RFC6126]. It requires the mandatory
sub-TLV introduced in [BABEL]. Consequently, this extension MUST NOT
be used with routers implementing RFC 6126, otherwise persistent
routing loops may occur.

6.1. Loop-avoidance

The extension defined in this protocol uses a new Mandatory sub-TLV
to carry the source prefix information. As discussed in Section 4.4
of [BABEL], this encoding ensures that non-source-specific routers
will silently ignore the whole TLV, which is necessary to avoid
persistent routing loops in hybrid networks.

Consider two nodes A and B, with A source-specific announcing a route
to (D, S). Suppose that B (non source-specific) merely ignores the
source prefix information when it receives the update rather than
ignoring the sub- whole TLV, and reannounces the route as D. This
reannouncement reaches A, which treats it as (D, ::/0). Packets
destined to D but not sourced in S will be forwarded by A to B, and
by B to A, causing a persistent routing loop:

(D,S) (D)
<-- <--
------ A ----------------- B
-->
(D,::/0)

6.2. Starvation and Blackholes

In general, discarding source-specific routes by non-source-specific
routers will cause route starvation. Intuitively, unless there are
enough non-source-specific routes in the network, non-source-specific
routers will suffer starvation, and discard packets for destinations
that are only announced by source-specific routers.

A simple yet sufficient condition for avoiding starvation is to build
a connected source-specific backbone that includes all of the edge
routers, and announce a (non-source-specific) default route towards
the backbone.

7. Protocol Encoding

This extension defines a new sub-TLV used to carry a source prefix by
the three following existing messages: Update, Route Request and
Seqno Request.

7.1. Source Prefix sub-TLV

Fields:

Type Set to TBD TBD[128] to indicate a Source Prefix sub-TLV.

Length The length of the body, exclusive of the Type and Length
fields.

Source Plen The length of the advertised source prefix. This MUST
NOT be 0.

Source Prefix The source prefix being advertised. This field's size
is (Source Plen)/8 rounded upwards.

The Source Prefix field's source prefix encoding (AE) is the same as the Prefix's. It is
defined by the AE field of the corresponding TLV.

Note that this sub-TLV is a Mandatory sub-TLV. The whole TLV MUST be
ignored if that TLV sub-TLV is not recognized as described in Section 4.4. recognized. Otherwise, routing loops
may occur. occur (see Section 6.1).

7.2. Source-specific Update

The source-specific Update is an Update TLV with a Source Prefix sub-
TLV. It advertises or retracts source-specific routes in the same
manner than routes with non-source-specific Updates (see [BABEL]).
This TLV A
wildcard retraction (Update with AE equals to 0) MUST NOT be attached to wildcard updates. carry a
Source Prefix sub-TLV.

Contrary to the destination prefix, this extension does not compress
the source prefix attached to Updates. The destination prefix uses
compression as defined in [BABEL] for Updates with Mandatory
extensions. However, as defined in
[BABEL] (Section 4.5), the compression is allowed for the destination
prefix of source-specific routes. Legacy implementation will
correctly update their parser state, state while ignoring the whole TLV
afterwards.

7.3. Source-specific (Route) Request

TODO:

A source-specific Route Request is a Route Request TLV with a Source
Prefix sub-TLV. It prompts the receiver to send an update for a
given pair of destination and source prefixes. It MUST
NOT be used to request a full routing table dump. The Source Prefix
sub-TLV of a A wildcard source-specific Route request
(Route Request (Request with AE equals to 0 and 0) MUST NOT carry a Source Prefix sub-TLV) MIGHT be ignored: a receiver
MIGHT reply by a full routing table dump.
sub-TLV.

7.4. Source-Specific Seqno Request

A source-specific Seqno Request is a Seqno Request TLV with a Source
Prefix sub-TLV. It is just like a Seqno Request for a
source-specific source-
specific route. It uses the same mechanisms described in [BABEL].

8. IANA Considerations

IANA is instructed requested to allocate TBD, a Babel sub-TLV type from the
range reserved for mandatory sub-TLVs [value 128 suggested], and to
add the following entry to the "Babel mandatory sub-TLV Types"
registry:

+------+---------------+-----------------+

9. Security considerations

The extension defined in this document adds a new sub-TLV to three
TLVs already present in the original Babel protocol. It does not by
itself change the security properties of the protocol.

10. References

10.1. Normative References

[BABEL] Chroboczek, J., "The Babel Routing Protocol", Internet
Draft draft-ietf-babel-rfc6126bis-02, May 2017.

[BCP84] Baker, F. and P. Savola, "Ingress Filtering for Multihomed
Networks", BCP 84, RFC 3704, March 2004.

[IETF-SSR]
Lamparter, D. and A. Smirnov, "Destination/Source
Routing", Internet Draft draft-ietf-rtgwg-dst-src-routing,
May 2017.

[RFC6126] Chroboczek, J., "The Babel Routing Protocol
(Experimental)", RFC 6126, February 2011.

10.2. Informative References

[SS-ROUTING]
Boutier, M. and J. Chroboczek, "Source-Specific Routing",
August 2014.

In Proc. IFIP Networking 2015. A slightly earlier
version is available online from
http://arxiv.org/pdf/1403.0445. http://arxiv.org/
pdf/1403.0445.

Authors' Addresses

Matthieu Boutier
IRIF, University of Paris-Diderot
Case 7014
75205 Paris Cedex 13, 13
France

Email: boutier@irif.fr

Juliusz Chroboczek
IRIF, University of Paris-Diderot
Case 7014
75205 Paris Cedex 13, 13
France

Email: jch@irif.fr