Cisco OL-4015-08 Manuel d'utilisateur Page 140

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492
Cross-Platform Release Notes for Cisco IOS Release 12.0S
OL-1617-14 Rev. Q0
Caveats
Resolved Caveats—Cisco IOS Release 12.0(32)S13
CSCsw47868
Symptoms: An IPv6 ping fails on an E3 Gigabit line card because of a PRECAM 1 Exception.
Conditions: This issue pertains to the dropping of IPv6 packets because of a precam exception on
the egress side. It looked as if the profile for IPv6 was wrong when IPv4 QoS was already applied
even on different subinterfaces on the same port.
Workaround:
1) Add/Remove an ACL.
2) Add/Remove the subinterface.
CSCsw64956
Symptoms: The no ppp lcp fast-start command is added to all PPP-encapsulation interfaces.
Conditions: This symptom is observed after a router is upgraded from Cisco IOS
Release 12.0(32)SY7 to the latest 32sy throttle image.
Workaround: There is no workaround.
CSCsx10140
Recent research
(1)
has shown that it is possible to cause BGP sessions to remotely reset by injecting
invalid data, specifically AS_CONFED_SEQUENCE data, into the AS4_PATH attribute provided
to store 4-byte ASN paths. Since AS4_PATH is an optional transitive attribute, the invalid data will
be transited through many intermediate ASes which will not examine the content. For this bug to be
triggered, an operator does not have to be actively using 4-byte AS support.
The root cause of this problem is the Cisco implementation of RFC 4893 (4-byte ASN support) -
this RFC states that AS_CONFED_SEQUENCE data in the AS4_PATH attribute is invalid.
However, it does not explicitly state what to do if such invalid data is received, so the Cisco
implementation of this RFC sends a BGP NOTIFICATION message to the peer and the BGP session
is terminated.
RFC 4893 is in the process of getting updated to avoid this problem, and the fix for this bug
implements the proposed change. The proposed change is as follows:
“To prevent the possible propagation of confederation path segments outside of a confederation,
the path segment types AS_CONFED_SEQUENCE and AS_CONFED_SET [RFC5065] are
declared invalid for the AS4_PATH attribute. A NEW BGP speaker MUST NOT send these path
segment types in the AS4_PATH attribute of an UPDATE message. A NEW BGP speaker that
receives these path segment types in the AS4_PATH attribute of an UPDATE message MUST
discard these path segments, adjust the relevant attribute fields accordingly, and continue
processing the UPDATE message.
The only affected version of Cisco IOS that supports RFC 4893 is 12.0(32)S12, released in
December 2008.
(1)
For more information, please visit:
http://www.merit.edu/mail.archives/nanog/msg14345.html
CSCsx32416
Symptoms: A session may go down one or more times before stabilizing in the up state.
Conditions: This symptom is observed when a BFD session is first coming up and the network is
suffering from congestion.
Workaround: There is no workaround.
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