Re: flow/packet loss through L3 C3560, pings OK

Discussion in 'Cisco' started by stephen, May 1, 2008.

  1. stephen

    stephen Guest

    "Phil Begriffenfeldt" <> wrote in
    message news:MoWdncFmX8mt04TVnZ2dnUVZ_gSdnZ2d@visi...
    > I have a Catalyst 3560G that is doing L3 routing. I tried to use it as
    > default gateway for a web cluster, which was doing about 120mbps of
    > traffic, 5kpps each in and out. However, users noticed slow page loads,
    > broken inline images, etc.
    >
    > I was able to ping all the servers from outside the 3560G with zero
    > packet loss in tens of thousands of 1500-byte pings. I moved the web
    > cluster to a C6509 (same interface config) and the issue disappeared.


    we had some issues with the 10/100 versions with buffer tuning where we had
    problems with traffic bursts overwhelming the buffers, esp when you turn QoS
    on as you effectively reduce the buffer pool for any 1 QoS type by 75%.

    If you have several GigE connected servers contending for a congested or
    rate limited port this could be an issue.

    there are some commands to look at the buffers - something like
    show platform port-asic statistics..... you want the drop stats for any
    overloaded outbound ports.
    >
    > Web client experience was noticably impacted, so if it were simple
    > packet loss, I think I would have seen it with ping. It seemed as
    > though the issue was related either to the type of traffic (plain http)
    > or flow (lots of flows).
    >
    > The 3560 has a pretty vanilla config; the web cluster traffic was being
    > routed between a "no switchport" interface and a Vlan interface. I did
    > notice that the "no switchport" interface had "ip route-cache
    > same-interface" configured, and I'm not sure why. Also, the 3560 is
    > carrying about 7k external routes, but I monitor it to make sure it
    > doesn't hit the limit. I didn't see any clues in syslog.


    you need "sdm prefer routing" in the config to handle lots of IP routes - if
    not they overflow the hardware forwarding table and get dealt with in
    software.
    >
    > Phil

    --
    Regards

    - replace xyz with ntl
    stephen, May 1, 2008
    #1
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  2. stephen

    stephen Guest

    "Phil Begriffenfeldt" <> wrote in
    message news:eaidnQwIL7Vqi4bVnZ2dnUVZ_rSrnZ2d@visi...
    > stephen wrote:
    > > you need "sdm prefer routing" in the config to handle lots of IP routes

    >
    > Thanks for reminding me. I did set that last May (it's logged), and
    > then power-cycled the switch, but I do not appear to have verified "show
    > sdm" after the power cycle. Now I see that the switch is using
    > default/desktop, which could be the source of my trouble. Weird.


    yes - hardware forwarding tables will fill with 1 to 2k routes.

    everything that arrives after the tables fill goes in software forwarding -
    so whether it is an irritation or a disaster depends on the order the routes
    arrive.

    Not a fun thing to trouble shoot, but it does log an "out of space"
    message - shame Cisco couldnt make it obvious what it is an error about....
    --
    Regards

    - replace xyz with ntl
    stephen, May 2, 2008
    #2
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