Cisco Cisco IOS Software Release 12.0(13)S7
Behavioral Change for Buffer Recarving
Behavioral Change to Carve-Level 1
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Behavioral Change for Buffer Recarving
Behavioral Change to Carve-Level 1
This section explains the behavioral change to carve-level 1 functionality. It contains the following
topics:
topics:
•
•
Old Behavior
The ToFab and FrFab of all line cards match the queues in the global buffer distribution (dsn).
New Behavior
At carve level 1, fix ensures change in largest MTU configured on slot, recarves both ToFab and FrFab
buffers on the same line card and only FrFab buffers on other card, keeping the ToFab buffers of other
card unchanged.
buffers on the same line card and only FrFab buffers on other card, keeping the ToFab buffers of other
card unchanged.
However, in some rare cases though global distribution changes due to MTU change, same will not be
reflected in the ToFab of other line card due above restriction. So, there could be some extra buffer
queues which are not in global buffer distribution.
reflected in the ToFab of other line card due above restriction. So, there could be some extra buffer
queues which are not in global buffer distribution.
Buffers are allocated dynamically for incoming packets. If incoming packet matches the criteria for extra
queue found in ToFab direction, it will allocate buffer from that queue. So buffers in extra queue(in
ToFab direction) do not go waste.
queue found in ToFab direction, it will allocate buffer from that queue. So buffers in extra queue(in
ToFab direction) do not go waste.
The following example shows the logs of caveat at carve level-1. The command output in the following
example shows that an extra buffer queue is added in ToFab for slot 2. The example includes the
following hardware and software configurations:
example shows that an extra buffer queue is added in ToFab for slot 2. The example includes the
following hardware and software configurations:
•
A router with three line cards available at slots 0, 2, and 3, respectively.
•
The default MTUs configured on slots 0, 2, and 3 are 4470, 1500, and 4470, respectively.
•
The initial maximum slot MTUs configured on slots 0, 2, and 3 are 4470, 9072, and 1500,
respectively. (These steps followed to produce the following output).
respectively. (These steps followed to produce the following output).
Step 1
At slot 3, change the maximum slot MTU to 1800 from the default value of 1500.
Step 2
At slot 2, change the maximum slot MTU from 9072 to the default value of 4470.
Step 3
At slot 3, change the maximum slot MTU from 1800 back to the default value of 1500.
Router# show controllers queues
Global MTU information:
Max MTU data size = 4592
MTUs considered in SDRAM buffer carving:
Index MTU Data Size
0 1568
1 4592
Input SDRAM buffer distribution = default :
Index Data Size Min Data Size Percent Buffers Fixed?
0 80 1 50 yes
1 608 81 30 yes