Cisco Cisco IOS Software Release 12.0 S

Cisco IOS Release 12.0(29)S1 is a rebuild of Cisco IOS Release 12.0(29)S. The caveats listed in this 
section are resolved in Cisco IOS Release 12.0(29)S1 but may be open in previous Cisco IOS releases. 
This section describes only severity 1 and 2 caveats.

CSCef46191

Symptoms: A specifically crafted Transmission Control Protocol (TCP) connection to a telnet or 
reverse telnet port of a Cisco device running Internetwork Operating System (IOS) may block 
further telnet, reverse telnet, Remote Shell (RSH), Secure Shell (SSH), and in some cases Hypertext 
Transport Protocol (HTTP) access to the Cisco device. Telnet, reverse telnet, RSH and SSH sessions 
established prior to exploitation are not affected.

All other device services will operate normally.

Conditions: User initiated specially crafted TCP connection to a telnet or reverse telnet port results 
in blocking further telnet sessions. Whereas, services such as packet forwarding, routing protocols 
and all other communication to and through the device remains unaffected.

Workaround: The detail advisory is available at 

CSCef40187

Symptoms: An SRP interface is stuck and there is no response at all. In the output of the show srp 
topology command, the last topology packet that is received takes more than five seconds to arrive. 
In addition, the “zero encap length” counter in the output of the show hardware pxf cpu stat 
interface srp 1/1 detail command increases.

Conditions: This symptom is observed on a Cisco 10720 when the value of the overall packet size 
divided by 32 is 1 or 2.

Workaround: There is no workaround. 

CSCef44154

Symptoms: When an MPLS packet that enters through an SRP or Ethernet interface contains an 
L2TP or UTI packet and this MPLS packet is processed by the RP instead of the PXF engine (for 
example, when the IP header in the MPLS packet contain options and the MPLS TTL equals 0 or 1), 
the SRP or Ethernet interface stops receiving packets.

Conditions: This symptom is observed on a Cisco 10720 that runs Cisco IOS Release 12.0S.

Workaround: There is no workaround. 

CSCef52419

Symptoms: In Cisco IOS software releases earlier than Cisco IOS Release 12.0(27)S3, 
Release 12.0(28)S1, and Release 12.0(30)S, the CPU utilization of a Cisco 10720 is high (x%/y%, 
where y is greater than 60 percent), and continuous BGP and LDP flapping is reported. The counters 
in the output of the show interface command show a large number of drops and the output of the 
show buffers command shows a large number of cache misses for the private IBC buffer pools.