Internet DRAFT - draft-wang-idr-bgp-error-enhance
draft-wang-idr-bgp-error-enhance
Interdomain Routing Working Group H. Wang
Internet-Draft M. Shen
Intended status: Standards Track J. Dong
Expires: 27 April 2022 Huawei Technologies
24 October 2021
Revised Error Handling for BGP Messages
draft-wang-idr-bgp-error-enhance-00
Abstract
This document supplements and revises RFC7606. According to RFC
7606, when an UPDATE packet received from a neighbor contains an
attribute of incorrect format, the BGP session cannot be reset
directly. Instead, the BGP session must be reset based on the
specific problem. Error packets must minimize the impact on routes
and do not affect the correctness of the protocol. Different error
handling methods are used. The error handling methods include
discarding attributes, withdrawing routes, disabling the address
family, and resetting sessions.
RFC 7606 specifies the error handling methods of some existing
attributes and provides guidance for error handling of new
attributes.
This document supplements the error handling methods for common
attributes that are not specified in RFC7606, and provides
suggestions for revising the error handling methods for some
attributes. The general principle remains unchanged: Maintain
established BGP sessions and keep valid routes updated. However,
discard or delete incorrect attributes or packets to minimize the
impact on the current session.
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.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Error-Handling Procedures Update for NLRI . . . . . . . . . . 4
3.1. Prefix Length Error . . . . . . . . . . . . . . . . . . . 4
3.2. Appears More Than Once . . . . . . . . . . . . . . . . . 4
4. Error-Handling Procedures Update for Existing Attributes . . 5
4.1. Nexthop . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.2. MP_REACH_NLRI . . . . . . . . . . . . . . . . . . . . . . 5
4.3. Prefix SID . . . . . . . . . . . . . . . . . . . . . . . 6
4.4. AGGREGATE and AS4_AGGREGATOR . . . . . . . . . . . . . . 6
4.5. ORIGINATOR_ID . . . . . . . . . . . . . . . . . . . . . . 6
4.6. Cluster-List . . . . . . . . . . . . . . . . . . . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
7.1. Normative References . . . . . . . . . . . . . . . . . . 7
7.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
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1. Introduction
According to RFC 4271, a BGP session that receives an UPDATE message
containing a malformed attribute needs to reset the session that
receives the malformed attribute.
According to our experience during maintenance, malformed packets may
be incorrectly encapsulated due to software bugs or mis-understanding
of standards in software development. Interrupting a neighbor causes
neighbor flapping, which does not help solve the problem. The
malformed packets may not be recognized by intermediate routers and
cannot be incorrectly checked and propagated to other routers that
establish sessions. When they reach the router that recognizes and
checks the attribute, the neighbor flapping may also occured. Even
because routes are propagated multiple times, a route containing
malformed packets may be received from multiple sessions at a
checkpoint, causing multiple sessions to be reset, and the harm is
multiplied.
For the preceding reasons, RFC 7606 defines a new method for
processing incorrect UPDATE packets. If the Update packet received
from a neighbor contains incorrect attributes, the BGP session cannot
be reset directly. Instead, the BGP session needs to be handled in a
specific manner based on the principle that incorrect packets affect
routes as little as possible and do not affect protocol correctness.
The error handling methods include discarding attributes, withdrawing
routes, disabling the address family, and resetting sessions.
However, the error handling methods of some common attributes are not
provided in RFC7606 or are different from those of vendors. This
document supplements the error handling methods of some common
attributes and provides suggestions for modifying the error handling
methods of some attributes.
2. Scenarios
+-----+ +-----+ +-----+
| RT1 |----| RR |---| RT2 |
+-----+ +-.---+ +-----+
|
\
+-----+
| RT3 |
+-----+
Figure 1 A simple network
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Figure 1 shows a simple network. When RT3 has some software bugs or
misunderstands the RFC, it may send a malformed packet. The RR
receives the packet and considers it a malformed packet according to
the error handling rules and resets the session. Later the session
between RT3 and RR is re-established. RT3 will resend the packet to
RR, and RR continues to repeat the previous action. This will happen
continuously until the operator modifies the configuration, such as
deleting the configuration about that new feature of the property,
and sometimes they don't know how to correct the problem. During
this process, RT3 services are unavailable. Frequent neighbor
reestablishment and route updating also consumes more RR's system
resources.
If the RR does not understand the attribute, the RR sends packets to
RT1 and RT2. RT1 and RT2 may perform the same operation as RR. As a
result, services between RT1 and RT2 are interrupted.
3. Error-Handling Procedures Update for NLRI
3.1. Prefix Length Error
According to [RFC7606], when a NLRI/UNLRI or MP_REACH_NLRI/
MP_REACH_UNLRI with invalid length, eg, IPv4 Prefix length is more
than 32, we must drop this Prefix and ignore the following Prefixes.
We may keep the prefixes we have parsed correctly before.
Then we may also try to continue parse the next update packet if we
can correctly find it.
The NLRI/UNLRI or MP_REACH_NLRI/MP_REACH_UNLRI with invalid length is
malformed.
3.2. Appears More Than Once
[RFC7606] described like this:
If the MP_REACH_NLRI attribute or the MP_UNREACH_NLRI [RFC4760]
attribute appears more than once in the UPDATE message, then a
NOTIFICATION message MUST be sent with the Error Subcode "Malformed
Attribute List".
Revised suggestion:
If the MP_REACH_NLRI attribute or the MP_UNREACH_NLRI [RFC4760]
attribute appears more than once in the UPDATE message, only the last
MP_REACH_NLRI/MP_UNREACH_NLRI SHOULD be processed, the others would
be ignore.
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4. Error-Handling Procedures Update for Existing Attributes
4.1. Nexthop
[RFC4271] define the IP address in the NEXT_HOP meet the following
criteria to be considered semantically incorrect:
a) It is the IP address of receiving speaker.
b) The IP address is not EBGP directly neighbor's address or not
share a common subnet with the receiving BGP speaker.
An update message with the case a) MAY be install to the RIB but
treat as invalid.
Whether an update message with the case b) SHOULD be considered
semantically incoorect depends on the user's configuration.
The following criteria also must to be considered semantically
incorrect:
c) The IP address is all zero.
d) The IP address is all one.
e) The IP address is multicast address(Class D) or reserved address
(Class E).
f) The IP address is not a invalid ip address.
An update message with the case c) to f) SHOULD be logged, and the
route will be treat-as-withdraw.
4.2. MP_REACH_NLRI
[RFC7606] suggest to do "session reset" or "AFI/SAFI disable"
approach. But this approach is too strict.
If the Length of Next Hop Network Address field of the MP_REACH
attribute is inconsistent with that which was expected, the attribute
is considered malformed. The whole MP_REACH attribute will be ignore
and try to parse the next update packet. When it cannot correctly
locate the next update packet, it will do the procedure suggested
according to [RFC7606] . Otherwise, only the error SHOULD be logged
and continued to do packet parsing.
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An update message may both contained MP_REACH_NLRI and
MP_REACH_UNLRI. If there are same Prefixes in both MP_REACH_NLRI and
MP_REACH_UNLRI, the message SHOULD NOT be consider malformed. In
this case, it should be firstly process the Prefixes in the
MP_REACH_NLRI then process the Prefixes in the MP_REACH_UNLRI.
4.3. Prefix SID
According to [RFC8669], an update message containing a malformed or
invalid BGP Prefix-SID attribute will be ignore and not advertise it
to other BGP peers. But this procedure may lead to unexpected
results.
The error handling is revised to be treat-as-withdraw.
4.4. AGGREGATE and AS4_AGGREGATOR
When the router-id in AGGREGATE or AS4_AGGREGATE attibute is zero,
the attribute SHOULD be consider semantically incorrect, and the
attribute SHOULD be logged and discard.
4.5. ORIGINATOR_ID
The error handling of [RFC4456] and [RFC7606] is revised as follows.
When the BGP Identifier in ORIGINATOR_ID attibute is zero, the
attribute SHOULD be consider semantically incorrect, and the
attribute SHOULD be logged and the UPDATE message SHALL be handled
using the approach of "treat-as- withdraw".
4.6. Cluster-List
The error handling of [RFC4456] and [RFC7606] is revised as follows.
When the CLUSTER_ID value in ORIGINATOR_ID attibute is zero, the
attribute SHOULD be consider semantically incorrect, and the
attribute SHOULD be logged and the UPDATE message SHALL be handled
using the approach of "treat-as- withdraw".
5. IANA Considerations
This document makes no request of IANA.
6. Security Considerations
This document helps reduce the impact of malformed packets on the
network and devices.
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7. References
7.1. 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>.
7.2. Informative References
[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>.
[RFC4456] Bates, T., Chen, E., and R. Chandra, "BGP Route
Reflection: An Alternative to Full Mesh Internal BGP
(IBGP)", RFC 4456, DOI 10.17487/RFC4456, April 2006,
<https://www.rfc-editor.org/info/rfc4456>.
[RFC7606] Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K.
Patel, "Revised Error Handling for BGP UPDATE Messages",
RFC 7606, DOI 10.17487/RFC7606, August 2015,
<https://www.rfc-editor.org/info/rfc7606>.
[RFC8669] Previdi, S., Filsfils, C., Lindem, A., Ed., Sreekantiah,
A., and H. Gredler, "Segment Routing Prefix Segment
Identifier Extensions for BGP", RFC 8669,
DOI 10.17487/RFC8669, December 2019,
<https://www.rfc-editor.org/info/rfc8669>.
Authors' Addresses
Haibo Wang
Huawei Technologies
Huawei Campus, No. 156 Beiqing Road
Beijing
100095
China
Email: rainsword.wang@huawei.com
Ming Shen
Huawei Technologies
Huawei Campus, No. 156 Beiqing Road
Beijing
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100095
China
Email: shenming2@huawei.com
Jie Dong
Huawei Technologies
Huawei Campus, No. 156 Beiqing Road
Beijing
100095
China
Email: jie.dong@huawei.com
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