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Cross-Platform Release Notes for Cisco IOS Release 12.0S

OL-1617-14 Rev. Q0

Caveats

Resolved Caveats—Cisco IOS Release 12.0(32)S2

Workaround: There is no workaround to prevent the symptom from occurring. When the symptom

has occurred, enter the shutdown interface configuration command followed by the no shutdown

interface configuration command on the OC-12 ATM interface to enable the VC to become active.

• CSCsc30369

Symptoms: A cBus Complex Restart may occur on a Cisco 7500 series when you leave the interface

configuration mode after you have changed the encapsulation on a serial interface from HDLC to

another encapsulation type such as PPP or Frame Relay.

The maximum datagram for an interface a of low-speed serial port adapter with HDLC

encapsulation and an MTU of 1500 is 1528 because the overhead that is added to the MTU is 28.

The maximum datagram for an interface a of high-speed serial port adapter with HDLC

encapsulation and an MTU of 1500 is 1530 because the overhead that is added to the MTU is 30.

When the encapsulation type is changed, the maximum datagram size may change, which causes an

internal MTU change. This situation may cause some packets to be dropped as giants.

Conditions: This symptom is observed after the first change to the type of encapsulation from the

default of HDLC to another encapsulation type when you leave the interface configuration mode.

Subsequent changes to the type of encapsulation do not cause the cBus Complex Restart.

Workaround for the cBus Complex Restart: There is no workaround for the cBus Complex Restart.

An MTU change on a Cisco 7500 series results in a cBus Complex Restart, which usually means a

router outage of 15 to 30 seconds or a minute and a half, depending on the Cisco IOS software image

that the router is running.

Workaround for the packet drops: Reconfigure the MTU to prevent packet from being dropped as

giants.

Further Problem Description: The fix for this caveat ensures the maximum datagram for an interface

a of low-speed serial port adapter with HDLC encapsulation and an MTU of 1500 is 1608 to allow

for an overhead to the MTU of 108. The maximum datagram for an interface a of high-speed serial

port adapter with HDLC encapsulation and an MTU of 1500 is then 1610 to allow for an overhead

to the MTU of 110.

• CSCsc71286

Symptoms: The throughput is far below what you would expect on an MFR bundle that is configured

on a 8-port multichannel T1/E1 PRI port adapter (PA-MC-8TE1+).

Conditions: This symptom is observed on a Cisco 7200 series that runs Cisco IOS

Release 12.0(31)S2 when the MFR bundle has four T1 links, three of which are shut down. When

you generate 2.5 Mbps of traffic to congest the one active link, a throughput of about 37 kbps to 59

kbps is observed. You would expect a throughput of about 1.5 Mbps.

Workaround: There is no workaround. The symptom does not occur in Release 12.3.

IP Routing Protocols

• CSCsb50606

Symptoms: Memory utilization in the “Dead” process grows gradually until the memory is

exhausted. The output of the show memory dead command shows that many “TCP CBs” re

allocated. Analysis shows that these are TCP descriptors for non-existing active BGP connections.

Conditions: This symptom is observed on a Cisco 7200 series that runs Cisco IOS Release 12.3(13),

that has an NPE-G1, and that functions as a PE router with many BGP neighbors. However, the

symptom is not platform-specific, nor release-specific.

Workaround: Reload the router. I this is not an option, there is no workaround.

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