Yes, you can adjust how many buffers of each size the router maintains.
Buffer tuning is somewhat risky, though. You might want to talk to TAC first.
By the way, in my previous message, I prefaced my comments with, "If you
can believe the CIT class." I'm not sure you can believe that class. &;-)
For more info on buffers, see the following Web page written by TAC. It
might be more reliable.
http://www.cisco.com/warp/public/63/buffertuning.html
Priscilla
P.S. Please send messages to the group. I can't always answer questions
sent to my individual address.
At 12:32 PM 12/13/00, Vasudeva Venkateshaiah wrote:
>Hi..
>
>Can the size of these buffers be increased or decreased? If I know what is
>the kind of packet/traffic going thro' my router, so that I make use of all
>the buffers and not load my router with only 2 buffers.
>
>Thanks.
>
> -----Original Message-----
>From: Priscilla Oppenheimer [mailto:[EMAIL PROTECTED]]
>Sent: Wednesday, December 13, 2000 11:28 AM
>To: CCIE TB; [EMAIL PROTECTED]
>Subject: Re: Why so many buffers ?
>
>If you can believe the CIT class, the small, middle, big, very big, large,
>and huge buffers are used for process switching. These are the buffers that
>you track with the "show buffers" command. These buffers are in system
>memory and they generally get used if you have disabled fast switching and
>other performance-enhancing forwarding methods.
>
>System buffers are also used for packets that the router itself generates,
>such as ICMP packets, routing protocol updates, SNMP, and Novell IPX SAP
>updates.
>
>With process switching, when a packet arrives at an interface, the
>processor is interrupted for the time it takes to copy the packet from the
>interface buffer to system memory. The processor looks up the Layer-3
>destination address in the routing table to determine the exit interface.
>The packet is rewritten with the correct header for that interface and
>forwarded to the interface. At this time, an entry is also placed in the
>fast-switching cache so that subsequent packets for the destination address
>can use the same header.
>
>With fast-switching, a packet is handled immediately, without scheduling an
>interrupt of the system processor and without using those small, medium,
>big, etc. system buffers.
>
>Having different size buffers means that memory is used efficiently.
>Packets come in different sizes. Why waste a 1500-byte buffer for Telnet
>packets, which are only 64 bytes, typically? Or another example is
>AppleTalk packets, which are always 600 bytes or less. IPX used to use
>600-byte packets, though Large IPX has been around for a while. IPX SAP
>packets are still only about 600 bytes if I remember correctly. Many
>distance-vector routing protocols also use packets in the 512-600 byte
>ranges for their routing updates. Database applications use medium-sized
>packets usually. HTTP also often uses medium-sized packets, especially if
>the browser uses multiple TCP sessions to download information.
>
>If you are process-switching and there are lots of dropped packets, you can
>issue a "show buffers" command and determine which size packets are causing
>the problems. Knowing the size of the packets that are getting dropped
>helps you identify which protocols are the culprits.
>
>Priscilla
>
>
>
>At 11:36 PM 12/12/00, CCIE TB wrote:
> >Hi,
> >
> >There are many buffers on Cisco routers like small, middles, big, ....
> >1. Is there any advantage/disadvantage of having many buffers compared to
> >having one or two only.
> >2. How and in what order they are being used by the system ?
> >
> >Any feedback is highly appreciated.
> >
> >Adia
> >
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>________________________
>
>Priscilla Oppenheimer
>http://www.priscilla.com
>
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