Internet DRAFT - draft-li-idr-inter-protocol-anti-loop
draft-li-idr-inter-protocol-anti-loop
Network Working Group W. Li
Internet-Draft L. Wang
Intended status: Standards Track Huawei Technologies
Expires: 4 September 2023 3 March 2023
Loop prevention for route import between protocols
draft-li-idr-inter-protocol-anti-loop-00
Abstract
BGP and IGP are commonly used network protocols during network
construction. At the beginning of BGP protocol design, EBGP and IBGP
loop prevention are considered. Similarly, the IGP protocol has a
loop prevention mechanism. In actual deployment, some or even all
routes of the two protocols are imported to each other. Route import
causes the loss of the anti-loop attribute of the protocol. As a
result, the anti-loop fails.
This document provides a feasible solution to the above problems.
Attribute information is added when routes are imported between
protocols. The added attribute information can be advertised to
neighboring neighbors through BGP peers or IGP peers. How the new
attributes are advertised using IGP peers is beyond the scope of this
article.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
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
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Drafts is at https://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 4 September 2023.
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Copyright Notice
Copyright (c) 2023 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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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Route Origin Site List Attribute . . . . . . . . . . . . . . 3
2.1. Route Origin Site List Attribute sub-TLVs . . . . . . . . 4
2.1.1. BGP Route Origin Site sub-TLV . . . . . . . . . . . . 4
2.1.2. OSPF Route Origin Site sub-TLV . . . . . . . . . . . 5
2.2. Route Origin Site List Attribute Advertisement . . . . . 6
2.3. Usage of Route Origin Site List Attribute . . . . . . . . 6
3. Error Handling . . . . . . . . . . . . . . . . . . . . . . . 6
4. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
8.1. Normative References . . . . . . . . . . . . . . . . . . 8
8.2. References . . . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
During actual network deployment or operation and maintenance, it is
common to import BGP and IGP routes to each other. In practice,
engineers must have a good understanding of network planning and
network status. If they are not careful, routing loops may occur.
The following figure shows an example:
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+---+
|RT2|
+---+
/ |
--IBGP--/ |
/ |
/ |
/ |
+---+ +---+ |
|RT1|----IBGP----|RR | IGP
+---+ +---+ |
\ |
\ |
\ |
--IBGP--\ |
\ |
+---+
|RT3|
+---+
As shown in the figure, RT1 imports routes and advertises the routes
to the RR. The RR advertises the routes to RT2 through an IBGP peer.
IGP imports BGP routes on R2 and advertises the routes to RT3. In
this case, the BGP anti-loop attribute information is lost. On RT3,
BGP imports IGP routes. RT3 preferentially selects the locally
imported routes and advertises the routes to the RR through IBGP.
The RR selects the route from RT3 and advertises routing updates to
RT2. As a result, a routing loop occurs.
This document provides a mechanism to prevent loops caused by route
import between protocols. This mechanism is implemented through a
new attribute, which we call the route origin site List attribute.
This attribute is transmitted between protocols when routes are
imported to each other and can be advertised to neighbors. When a
neighbor receives a route, it checks whether the local protocol route
origin site information is contained in the route origin site
attribute. If yes, a routing loop occurs.
How IGP advertises and generates protocol site attributes is beyond
the scope of this document. How to transfer route origin site
attributes between BGP and IGP is beyond the scope of this document.
2. Route Origin Site List Attribute
The attribute encoding content of the Route Origin Site List is the
information about the site where the route enters the BGP routing
table or IGP routing table for the first time.
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The Route Origin Site List attribute is optional and transitive.
Since the route may pass through multiple sites, the attribute length
field should be 2 bytes, that is, the extended length flag[RFC4271]
bit should be set.
The Route Origin Site List attribute contains one or more sub-TLVs.
The Route Origin Site List attribute are defined as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Attr.Flags | Attr.Type Code| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-TLVs |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* Attr.Flags: Optional-transitive, extended length bit is set, refer
to [RFC4271].
* Attr.Type Code: TBD.
* Length: 2 bytes. Indicates the total length of the sub-TLVs.
* sub-TLVs: Variable length, containing one or more sub-TLVs.
2.1. Route Origin Site List Attribute sub-TLVs
A sub-TLV on the originating node of a route, indicating that the
route is imported to each other, for example, BGP imports IGP routes.
The sub-TLVs is optional and may be present multiple times in the
Route Origin Site List.
When a route is advertised, the sub-TLV should be added to the Route
Origin Site List of the route. The receiver should check whether a
loop occurs on the route according to the Route Origin Site List
attribute of the route. Similarly, when importing a route, the
protocol checks whether a loop occurs on the route according to the
Route Origin Site List.
2.1.1. BGP Route Origin Site sub-TLV
This type of sub-TLV indicates that the route that carries this
attribute is imported to BGP from other protocols at the site.
The sub-TLV codes are as follows:
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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 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| VPN ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol Site ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* Type: 1.
* Length: Specifies the length of the value field in terms of
octets. The value MUST be 8.
* VPN ID: 4 octets of vpn instance ID. Indicates the VPN to which
the route is imported.
* Protocol Site ID: 4 octets. Identifies the protocol site on which
the route is imported to BGP. It is recommended that the site ID
be generated as a random number.
2.1.2. OSPF Route Origin Site sub-TLV
This type of sub-TLV indicates that the route that carries this
attribute is imported to OSPF from other protocols at the site.
The sub-TLV codes are as follows:
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 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Process ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol Site ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* Type: 2.
* Length: Specifies the length of the value field in terms of
octets. The value MUST be 8.
* Process ID: 4 octets. Indicates the OSPF process to which the
route is imported.
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* Protocol Site ID: 4 octets. Identifies the protocol site on which
the route is imported to OSPF. It is recommended that the site ID
be generated using a random number or ospf router-id.
2.2. Route Origin Site List Attribute Advertisement
For a route imported from one protocol to another, the local Route
Origin Site information SHOULD be added to the Route Origin Site List
attribute when the protocol advertises the route. The attribute of a
route received from a neighbor SHOULD not be modified when the route
is forwarded to other neighbors. To prevent inter-AS loops, the
local Route Origin Site information needs to be added to the
attribute of the Route Origin Site List for the scenario where the
route is received from the neighbor and forwarded to the EBGP
neighbor.
2.3. Usage of Route Origin Site List Attribute
When a route is received, the local Route Origin Site information
SHOULD be compared with the Route Origin Site List attribute of the
route to determine whether a loop occurs. If a routing loop occurs,
the protocol SHOULD be handled as follows:
* For the BGP protocol, the priority of routes with loops SHOULD be
lower than that of non-loop routes. Therefore, in the BGP route
selection rules, loop detection SHOULD be one of the route
selection rules, and this rule SHOULD be placed in a higher
priority position.
* For the OSPF protocol, the priority of routes with loops SHOULD be
lower than that of non-loop routes, and adjust the routing metric
to a larger value.
When routes are imported between protocols, the content of Route
Origin Site List attribute SHOULD be transferred to the peer
protocol. Each protocol advertises the attribute content to its
neighbors. The method used by other routing protocols to publish the
content of this attribute is not discussed in this document.
3. Error Handling
The validation of the TLVs/sub-TLVs introduced in this document and
defined in their respective sub-sections of Section 2 MUST be
performed to determine if they are malformed or invalid.
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In case of any error detected, either at the attribute or its TLV/
sub-TLV level, the "Attribute discard" strategy MUST be applied.
This is because this attribute is used for loop detection, and
abnormal attribute mishandling may cause more serious problems than
attribute discarding.
4. Use Cases
+---+
|RT2| [1,200]
+---+
/ |
--IBGP--/ |
/ |
/ |
[0,100] / |
+---+ +---+ |
|RT1|----IBGP----|RR | IGP
+---+ +---+ |
\ |
\ |
\ |
--IBGP--\ |
\ |
+---+
|RT3| [0,300]
+---+
As shown in the figure, RT1 imports the route, adds [0, 100] to the
Route Origin Site List attribute of the route, and advertises the
route to the RR through the IBGP peer.
The RR advertises the route to RT2 through the IBGP peer. The route
contains the Route Origin Site List attribute {[0, 100]}.
On RT2, OSPF process 1 imports BGP routes and advertises them to RT3
through the OSPF neighbor. The routes include {[1, 200], [0, 100]}.
[1, 200] is added by OSPF process 1.
On RT3, BGP imports OSPF routes that carry the {[1, 200], [0, 100]}
attribute. RT3 preferentially selects the locally imported route and
sends the route to the RR through an IBGP peer. The route carries
{[0, 300], [1, 200], [0, 100]}, [1, 300] is added by BGP.
The RR preferentially selects the route from RT3 and advertises a
route update carrying {[0, 300], [1, 200], [0, 100]} to RT2.
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After RT2 receives the route, OSPF process 1 imports BGP routes. BGP
sends the route with {[0, 300], [1, 200], [0, 100]} to OSPF. OSPF
compares [1,200] with {[0, 300], [1, 200], [0, 100]}, and finds that
a loop occurs in the route. After OSPF adjusts the route priority,
it advertises a low-priority route to RT3.
If there are other OSPF routes on RT3, other routes are preferred to
break the loop. Or, on RT3, when BGP imports OSPF routes containing
{[0, 300], [1, 200], [0, 100]}, it compares the [0,300] with {[0,
300], [1, 200], [0, 100]} to find routing loops and reduce the Route
selection priority. Therefore, the route sent by RR to RT3 takes
priority, and the loop is broken.
5. IANA Considerations
This document requests the creation of a new registry called "Route
Origin Site List Attribute" under the "BGP Path Attribute" registry.
Code Point Description
------- -------------------------------
TBD Route Origin Site List Attribute
The following initial Sub-TLV codepoints are assigned by this
document:
SubType Description
------- -------------------------------
1 BGP Route Origin Site sub-TLV
2 OSPF Route Origin Site sub-TLV
6. Security Considerations
There are no additional security risks introduced by this design.
7. Acknowledgements
8. References
8.1. 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>.
8.2. References
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[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
<https://www.rfc-editor.org/info/rfc4271>.
Authors' Addresses
Wenyan Li
Huawei Technologies
Huawei Campus, No. 156 Beiqing Road
Beijing
100095
China
Email: liwenyan@huawei.com
Lili Wang
Huawei Technologies
Huawei Campus, No. 156 Beiqing Road
Beijing
100095
China
Email: lily.wong@huawei.com
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