Internet DRAFT - draft-shyam-vlsmtrp
draft-shyam-vlsmtrp
INTERNET DRAFT S. Bandyopadhyay
draft-shyam-vlsmtrp-01.txt November 06, 2021
Intended status: Experimental
Expires: May 06, 2021
VLSM Tree Routing Protocol
draft-shyam-vlsmtrp-01.txt
Abstract
This is a light weight routing protocol applicable inside a network
that appears in the form of a tree and distribution of address space
takes place with the approach of VLSM. It is based on setting default
route inside VLSM tree. With this approach, routing information of
the external world need not be passed down to the VLSM tree. Thus,
load inside a router gets reduced substantially. This document
includes IP-VPN with MPLS inside VLSM tree by extending RSVP-TE.
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
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 06, 2022.
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Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
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1. Introduction
This is a light weight routing protocol of provider network that
appears in the form of a tree and distribution of address space takes
place with the approach of VLSM. It is based on setting default route
inside VLSM tree. Inside a VLSM tree, all the physical ports of a
switch are configured with their associated domain (i.e.
NetAddress/NetMask). Routing table will contain static routes based
on the entries configured on these ports. With this approach, routing
information of the external world need not be passed down to the VLSM
tree. Thus, load inside a router gets reduced substantially. In
order to support network management and explicit route option, root
of the tree maintains an image of the entire tree. A section of the
OSPF protocol without the SPF part is extended to get the image of
the tree at the root. This protocol is intended to be used in a real
IP environment (e.g. NAT free environment with IPv6 or any new
generation IP that may be emerged), but, it makes use of existing 32
bits address space for illustration. It expects addressing
architecture of real IP space to have separate address space assigned
for the routers; e.g. section 3.2.1 of architectural specification[1]
states that address space with prefix "111" will be assigned for the
routers. This document includes IP-VPN with MPLS inside VLSM tree by
extending RSVP-TE.
2. Setting default route inside VLSM tree
As it has been stated earlier, there is no need to pass down the
routing information of the external world inside a VLSM tree that
acts as a stub. Inside a VLSM tree, a node of higher prefix can be
divided into number of nodes with lower prefixes. Each divided node
can further be subdivided with nodes of further lower prefixes. This
process can be continued as long as it is desired or no more division
is further possible.
Following figure shows a typical arrangement of VLSM tree of a
service provider's network with IPv4 address space. Switch SW-A is
connected to the outside world and maintains global routing table. It
acts as the root of a VLSM tree that acts as a stub. It has been
assigned an address block 11.1.16.0/20 which is distributed among its
four children SW-B, SW-C, SW-D and SW-E with the approach of VLSM.
Switch SW-B further divides its address space between switches SW-F
and SW-G. Switch SW-F assigns an address block 11.1.16.0/24 to
customer network CN-A. Switch SW-G assigns address block 11.1.20.0/24
and 11.1.21.0/24 to two customers CN-B and CN-C; where as switch SW-E
assigns address block 11.1.30.0/24 to customer network CN-D.
Routing inside the tree takes place with the following principle.
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Inside the tree, if a node (switch/router) that is assigned a domain
(NetAddr/NetMask) receives a packet which is destined to somewhere
outside of its domain, needs to forward the packet to its parent in
the hierarchy.
+--------------+
| SW-A |
| 11.1.16.0/20 |
+-+-+------+-+-+
| | | |
+---------------+ | | +----------------+
| | | |
+------+-----+ +---------+--+ +-+----------+ +-----+------+
| SW-B | | SW-C | | SW-D | | SW-E |
|11.1.16.0/21| |11.1.24.0/22| |11.1.28.0/23| |11.1.30.0/23|
+---+----+---+ +------------+ +------------+ +--+---------+
| | |
| +-------+ |
| | +--+--+
+-------+----+ +----+-------+ |CN-D |
| SW-F | | SW-G | +-----+
|11.1.16.0/22| |11.1.20.0/22| 11.1.30.0/24
+--+---------+ +--+------+--+
| | |
| | |
+--+--+ +--+--+ +-+---+
|CN-A | |CN-B | |CN-C |
+-----+ +-----+ +-----+
11.1.16.0/24 11.1.20.0/24 11.1.21.0/24
If a host in CN-A wants to send a packet to an address 11.1.21.116,
CE router of CN-A forwards it to SW-F. SW-F finds the destination
address of the packet to be outside of its domain and forwards the
packet to its parent SW-B. SW-B finds that a port that has been
configured with the matching destination address and forwards it to
its child SW-G. Switch SW-G sends the packet to customer network CN-
B.
If a host in CN-B wants to send a packet to 11.1.17.120, CE router of
CN-B forwards the packet to SW-G. SW-G finds the destination address
of the packet to be outside of its domain and forwards the packet to
its parent SW-B. SW-B finds that a port that has been configured with
the matching destination address and forwards the packet to its child
SW-F. SW-F finds the destination address to be within its domain, but
no port has been configured with the matching destination address and
generates ICMP UNREACHABLE.
If a host in CN-C wants to send a packet to 16.2.22.116, CE router of
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CN-C forwards the packet to SW-G. SW-G finds the destination address
of the packet to be outside its domain and forwards the packet to SW-
B. SW-B forwards the packet to its parent SW-A. SW-A find the
destination address of the packet to be outside its domain and
consults with the global forwarding table and forwards the packet
through the right port.
3. Router address space
Section 2.2.7 of RFC 1812 [2] states, "a router that
has unnumbered point to point lines also has a special IP address,
called a router-id in this memo. The router-id is one of the
router's IP addresses (a router is required to have at least one IP
address). This router-id is used as if it is the IP address of all
unnumbered interfaces."
A router-id is selected based on the domain (NetAddress/NetMask) that
it is associated with. The prefix of the domain gets embedded with in
the router-id. The least significant bits of the router-id will
contain the prefix. For a prefix of 'n' bits in a 32 bits address
space there will be 32-'n' bits at the beginning of the address.
Based on section 3.2.1 of the architectural specification[1], it
starts with the prefix "1111", followed by set of '1' bits and ends
with a '0' bit. Therefore, to get the prefix of the domain, router-id
needs to be traced from the MSB towards LSB till it encounters a '0'
bit. The rest of the bits till the end is the prefix. So, it expects
prefix to be at most (32-5) i.e. 27 bits (5=first four bits as "1111"
followed by '0'). So, minimum length of a domain that a router can be
assigned is 32. With this approach, locators (i.e routers) and
identifiers can be routed based on the same routing table. This can
be defined as association between locators and identifiers.
Add the following lines at the beginning of "ip forwarding" routine:
if destination address of the ip packet starts with 'router-id'
prefix {
if prefix length of the prefix embedded inside the destination
address of the ip packet is less than the prefix length of
the prefix embedded inside the router-id of the router itself {
forward the packet to the parent of the router;
}
else {
find a temporary destination address 'tempDest'
with the prefix embedded inside the destination
address followed by '0' bits at the end.
forward the packet to 'tempDest' with the forwarding
rules as stated in section 2.
} }
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4. Network management and support of explicit route option
Section 2 has shown how routing is achieved using static route table
based on the ports configured with their associated domain. Standard
routing protocols usually advertise networks based on which routing
table is constructed. There is no such need here. When a router
tries to establish a circuit with another, it may contact a PCE to
get the best possible route within a set of routes. On getting the
best possible path, it sets the circuit using explicit route option.
As there is only one path between any two nodes inside a tree,
setting explicit route option does not make any sense to communicate
between any two nodes within the same tree. It may be required to
communicate a node in one VLSM tree to a node in another VLSM tree.
To support this feature, root of a VLSM tree needs to maintain an
image of the entire tree. A PCE can get this image by contacting the
root of the tree. A network management system software also can get
the status of the entire tree by communicating with the root of the
tree.
This section shows how to construct the tree with the approach of
routing protocol. It adopts "Hello protocol" and authentication
mechanism of OSPF protocol leaving behind the SPF part and
introducing new message types relevant to VLSM tree.
The router at the root constructs the tree the way it appears in the
figure above. Every router in the tree is configured with the router-
id of the root i.e. the domain of the tree it belongs to. Whenever a
router adds a node (it may be a customer network or another router)
as a child, it sends an "Add Node" message. The message is sent to
the root. On getting an "Add Node" message, root traces the tree and
identifies the node with "Router ID" as specified in the message and
adds a node underneath. Similarly, whenever a node gets deleted, a
"Delete Node" message is sent to the root. On getting "Delete Node"
message, root deletes the entire sub-tree under that node in the
tree. Whenever a link goes down, a "Link Down" message is sent to the
root. On receiving "Link Down" message, root marks the link status as
not active. Whenever a link comes up, on receiving "Link Up" message,
root builds the subtree under the node whose link was down (if it
happens to be a router) and sets the status of the link as active.
This is to get the up-to-date status of the subtree whose link went
down. Root calls "GetSubtree" routine recursively to build the
subtree as follows:
void GetSubtree(struct TreeNode *node)
{
send "Get Child Nodes" message to the router designated by node.
for all the children under node, construct a TreeNode underneath.
for all the children as a router call GetSubtree(&childNode).
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}
Where TreeNode may be defined as:
struct TreeNode{
uint32 nodeId; /* RouterId, 32 bits in IPv4 */
uint16 nodeType /* Customer Network (1)/Router(2) */
uint16 noOfChildren; /* Number of children */
struct TreeNode *parent; /* pointer to the parent */
struct TreeNode *childList; /* List of child nodes */
struct TreeNode *nextSibling; /* Next sibling in childList */
uint16 linkStatus; /* Link status with parent UP(1)/Down(2) */
}
Root can also call "GetSubtree" routine for all of its child to build
the entire tree at the time of transition from old protocol to new or
whenever required.
4.1. VLSM tree routing protocol messages
It maintains same message format of OSPF protocol such that existing
source code can be directly ported. This section describes new
message types along with Hello message of OSPF. Please follow section
A.3.1 of OSPF specification [3] for OSPF message format.
Every message starts with a standard 24 byte header.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version # | Type | Packet length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Router ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Area ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Checksum | AuType |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Authentication |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Authentication |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Version #
The version number. This specification documents version 1
of the protocol.
Type
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The message types are as follows.
Type Description
________________________________
1 Hello
2 Add Node
3 Delete Node
4 Link Down
5 Link Up
6 Get Child Nodes
7 Acknowledgment
Packet length
The length of the protocol packet in bytes. This length
includes the standard header.
Router ID
The Router ID of the packet's source.
Area ID
This is not relevant here but has been retained to make use of
existing OSPF source code with least modification.
Checksum
The standard IP checksum of the entire contents of the packet,
starting with the packet header but excluding the 64-bit
authentication field. This checksum is calculated as the 16-bit
one's complement of the one's complement sum of all the 16-bit
words in the packet, excepting the authentication field. If the
packet's length is not an integral number of 16-bit words, the
packet is padded with a byte of zero before checksumming. The
checksum is considered to be part of the packet authentication
procedure; for some authentication types the checksum
calculation is omitted.
AuType
Identifies the authentication procedure to be used for the
packet. Authentication is discussed in Appendix D of OSPF
specification [3].
Authentication
A 64-bit field for use by the authentication scheme. See
Appendix D of OSPF specification for details.
4.1.1. The Hello packet
Hello packet is just same as defined in OSPF protocol. Please follow
Section A.3.2 of OSPF specification [3] for detail.
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4.1.2. The Add Node packet
An "Add Node" packet is generated when a router adds a node as its
child. A node can be a customer network or a router. The message
gets transported to the root. The receiving router sends back an
"Acknowledgment" message by changing the "Type" field as
Acknowledgment. The "Sequence Number" and "Router ID" field gets
verified on receiving the acknowledgment back. On receiving an "Add
Node" message, root adds a new node to the tree under the node
designated by "Router ID".
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version # | 2 | Packet length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Router ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Area ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Checksum | AuType |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Authentication |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Authentication |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Node Type | Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Node ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Node Type
Node type is Customer Network (1)/Router (2)
Sequence Number
Whenever a router generates an Add Node message it uses a Sequence
Number. Usually it increments the Sequence Number on completion of
the transaction.
Node ID
Node ID is the router ID of the domain associated with the
router/customer network.
4.1.3. The Delete Node packet
"Delete Node" message gets generated by a router when a child node
gets deleted. The message is sent to the root. On receiving "Delete
Node" message, root deletes the node (i.e. the entire subtree) under
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the node designated as "Node ID". All the fields of a "Delete Node"
packet are same as an "Add Node" packet apart from the Type(3) field.
4.1.4. The Link Down packet
"Link Down" message gets generated once a router fails to get "Hello"
from any of its child and declares the link to be as inactive. The
message is sent to the root. On receiving "Link Down" message root
marks the link in the tree to be inactive. All the fields of a "Link
Down" packet are same as an "Add Node" packet apart from the Type(4)
field.
4.1.5. The Link Up packet
"Link Up" message gets generated once a router starts getting "Hello"
messages from a child which was marked as inactive. The message is
sent to the root. On receiving "Link Up" message, root calls
"GetSubtree" routine for the node as designated by "Node ID" (if it
happens to be a router). It updates changes in the subtree and marks
the link as active. All the fields of a "Link Up" packet are same as
an "Add Node" packet apart from the Type(5) field.
4.1.6. The Get Child Nodes packet
"Get Child Nodes" packet gets generated by root to get all the
children under a router. Contents of the router is expressed as
follows:
Router ID of the router (32 bits in IPv4) +
Number of children of the router (16 bits) +
for each child of the router {
Type of the child (Customer Network/Router) (16 bits) +
Router ID of the child (32 bits in IPv4)
}
Exchange of router information is just same as the operation of
"Database Description" packet of OSPF (See section A.3.3 of [3]).
Format of "Get Child Nodes" packet is same as "Database Description"
packet of OSPF with the "Type" field set as 6.
4.1.7. The Acknowledgment packet
An "Acknowledgment" packet is sent to acknowledge that an "Add
Node"/"Delete Node"/"Link Up"/"Link Down" message has been received
to the sender. All the fields of an "Acknowledgment" packet are same
as an "Add Node" packet apart from the Type(7) field.
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5. IP VPN with MPLS inside VLSM tree
This section describes how to make IP VPN work inside VLSM tree
without using BGP.
RFC4364 [4] describes "IP VPN" with BGP/MPLS. To support VPN, PE
routers maintain per-site forwarding table. When a packet arrives
from an associated CE router, PE router consults with this forwarding
table to forward the packet. If the packet is supposed to be
forwarded to another site of VPN through the backbone, it uses two-
level label stack. The upper label is used to forward the packet from
ingress PE router to the egress PE router; where as, the inner label
is used for the egress PE router to identify the associated CE router
where the packet is supposed to be forwarded. BGP is used by the
Service Provider to exchange the routes of a particular VPN among the
PE routers that are attached to that VPN. Configuration takes place
on PE routers of both the sides of LSP. The simplest way to achieve
this is to configure these attributes manually on PE routers. In
order to have dynamic allocation of inner label, MPLS signaling
protocols (in place of BGP) need to be extended. Allocation of inner
label has to be done by the egress PE router. Same message that is
used for the assignment of upper label may be used for the assignment
of inner label. Inside the forwarding table, each entry contains the
forwarding destination address based on a set of destination
addresses (NetAddress/NetMask) of the IP packets received from
ingress CE router. While establishing inner label, ingress PE router
needs to send these attributes with the signaling message and the
egress PE router needs to validate those before assigning label.
5.1. Extension to RSVP-TE to support IP VPN inside VLSM tree
This section describes extension to RSVP-TE[5] to support dynamic
allocation of inner label of two-level label stack used to support
VPN services.
In order to establish LSP using RSVP-TE, ingress PE router sends Path
message to the egress PE router. Path message is augmented with a
LABEL_REQUEST object. Labels are allocated downstream and
distributed (propagated upstream) by means of RSVP Resv message. For
this purpose, the RSVP Resv message is extended with a special LABEL
object. In order to support VPN to establish the inner label, Path
message is augmented with a VPN_ATTRIBUTE label. Similarly, RSVP Resv
message is extended with a VPN_LABEL object. When an egress PE router
receives a Path message, it checks the presence of VPN_ATTRIBUTE
object. On finding this object, egress PE router checks the viability
of assignment of VPN label with the parameters from the VPN_ATTRIBUTE
object and the attributes that are already configured with the egress
PE router. If the test is positive, it assigns a VPN label and does
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the rest of the processing of LSP label assignment and sends the RSVP
Resv message with the extension of VPN_LABEL object towards the
ingress PE router. On receiving Resv message with VPN_LABEL object,
ingress PE router assigns VPN label along with the rest of the
processing of Resv message and completes the operation. VPN_ATTRIBUTE
and VPN_LABEL objects are described below.
VPN_LABEL class=<IANA_TBD1>, C-Type=1
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (inner label) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
VPN_ATTRIBUTE class=<IANA_TBD2>, C-Type=1
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Global Unicast Address of Ingress CE Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Global Unicast Address of Egress CE Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Net Address of Destination IP Packet |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Net Mask of Destination IP Packet |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The format of the Path message is as follows:
<Path Message> ::= <Common Header> [ <INTEGRITY> ]
<SESSION> <RSVP_HOP>
<TIME_VALUES>
[ <EXPLICIT_ROUTE> ]
<LABEL_REQUEST>
[ <VPN_ATTRIBUTE> ]
[ <SESSION_ATTRIBUTE> ]
[ <POLICY_DATA> ... ]
<sender descriptor>
<sender descriptor> ::= <SENDER_TEMPLATE> <SENDER_TSPEC>
[ <ADSPEC> ]
[ <RECORD_ROUTE> ]
The format of the Resv message is as follows:
<Resv Message> ::= <Common Header> [ <INTEGRITY> ]
<SESSION> <RSVP_HOP>
<TIME_VALUES>
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[ <RESV_CONFIRM> ] [ <SCOPE> ]
[ <POLICY_DATA> ... ]
[ <VPN_LABEL> ]
<STYLE> <flow descriptor list>
<flow descriptor list> ::= <FF flow descriptor list>
| <SE flow descriptor>
<FF flow descriptor list> ::= <FLOWSPEC> <FILTER_SPEC> <LABEL>
[ <RECORD_ROUTE> ]
| <FF flow descriptor list>
<FF flow descriptor>
<FF flow descriptor> ::= [ <FLOWSPEC> ] <FILTER_SPEC> <LABEL>
[ <RECORD_ROUTE> ]
<SE flow descriptor> ::= <FLOWSPEC> <SE filter spec list>
<SE filter spec list> ::= <SE filter spec>
| <SE filter spec list> <SE filter spec>
<SE filter spec> ::= <FILTER_SPEC> <LABEL> [ <RECORD_ROUTE> ]
Egress router generates an error with Error Code = 24, sub-code =
<IANA_TBD3> (VPN label allocation error) if the operation fails.
6. IANA Consideration
IANA has assigned RSVP class number <IANA_TBD1> for the object
VPN_LABEL and RSVP class number <IANA_TBD2> for VPN_ATTRIBUTE. IANA
has also assigned an error sub-code <IANA_TBD3> for VPN label
allocation error under Error Code = 24.
7. Security Consideration
This document does not include any security related issues.
8. Normative References
[1] S. Bandyopadhyay, "An Architectural Framework of the Internet
for the Real IP World" <draft-shyam-real-ip-framework-61.txt>
(work in progress).
[2] F. Baker, Ed.., "Requirements for IP Version 4 Routers",
RFC 1812, June 1995.
[3] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.
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[4] E. Rosen, Y. Rekhter, "BGP/MPLS IP Virtual Private Networks
(VPNs)", RFC 4364, February 2006.
[5] D. Awduche, L. Berger, D. Gan, T. Li, V. Srinivasan, G. Swallow,
"RSVP-TE: Extensions to RSVP for LSP Tunnels", RFC 3209,
December 2001.
9. Author's Address
Shyamaprasad Bandyopadhyay
HL No 205/157/7, Kharagpur 721305, India
Phone: +91 3222 225137
e-mail: shyamb66@gmail.com
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