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CSS: Different Ping Sizes

Hi, What I'm seeing is that some IP's are set for an MTU of 1472, while others are 34032 or 65500. How is this set and how can it be modified?

For Example:

circuit VLAN55

  ip address <----------- Can send ping of 34032 bytes

    ip virtual-router 55
    ip virtual-router 150 priority 105 preempt
    ip redundant-interface 55 <------------- Can only send ping of 1472 bytes

circuit VLAN255

  ip address <----------- Can send ping of 34032 bytes
    ip virtual-router 255
    ip redundant-interface 255 <------------- Can only send ping of 1472 bytes

circuit VLAN256

  ip address <----------- Can send ping of 34032 bytes
    ip virtual-router 254
    ip redundant-interface 254 <------------- Can only send ping of 1472 bytes

The VIP’s and real IP’s of the servers are exhibiting similar results.

Thank you in advance!


Cisco Employee

Re: CSS: Different Ping Sizes

Unfortunately, there is no option to enable ping more than 1472 bytes on redundant-interface.

CSS supports packets over 1500 bytes on the circuit ip address and mgmt ip address, but

there is a limitation on the redundant-interface ip address or any other ip address.

data(1472bytes) + icmp header(8bytes) + ip header(20bytes) = 1500 bytes

Since redundant-interface and vip address are virtual address, the behavior is different from

circuit ip address and mgmt address. You can check with 'shell 1 1 ifShow | grep Internet'

command whether the ip address is supported more than 1500 bytes or not

CSS11503(debug)# shell 1 1 ifShow | grep Internet

     Internet address:  <<==  Ethernet-Mgmt

     Internet address:  <<== loopback

     Internet address:  <<== circuit ip address

<<== ip address of redundant-interface is not present

<<== vip address is not present


CSS11503(debug)# sh run circuit

!************************** CIRCUIT **************************

circuit VLAN777

  ip address

    ip virtual-router 1

    ip redundant-interface 1

CSS11503(debug)# sh run owner

!*************************** OWNER ***************************

owner test

  content test

    vip address

    add service sv1

    add service sv2


CSS11503(debug)# sh boot-config

!************************ BOOT CONFIG ************************

  ip address

  subnet mask

  primary boot-file sg0820402

  primary boot-type boot-via-disk

CSS can handle and loadbalance fragments to vip address with 'tcp-ip-fragment-enabled' 
and udp-ip-fragment-enabled' command on global configuration mode, but it doesn't affect
icmp packets.

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