Layer 3 fragmentation

Unanswered Question
Jan 30th, 2008
User Badges:

Hi,

Is fragmentation taken care on layer 3 switch compared to a router.

I have 2 deafult gateways in my network, one is on the router and the other on the switch which are in the same VLAN.

When i try to access the other side of the network which is a different subnet, by using the router interface as default gateway then i have good connectivity, but if i use the switch SVI as the default gateway the i face performance issues.i can see no errors or drops across any ports.


  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 2 (1 ratings)
Loading.
Edison Ortiz Wed, 01/30/2008 - 09:18
User Badges:
  • Super Bronze, 10000 points or more
  • Hall of Fame,

    Founding Member

How do you know for sure you are fragmenting the packet ?


You can test by initiating a ping from a workstation with a large packet.


For instance,


C:\>ping -l 1500 x.x.x.x -f


Pinging x.x.x.x with 1500 bytes of data:


Packet needs to be fragmented but DF set.

Packet needs to be fragmented but DF set.


C:\>ping -l 1273 x.x.x.x -f


Pinging x.x.x.x with 1273 bytes of data:


Packet needs to be fragmented but DF set.


C:\>ping -l 1272 x.x.x.x -f


Pinging x.x.x.x with 1272 bytes of data:


Reply from x.x.x.x: bytes=1272 time=28ms TTL=237


__


As you can see, I can't send packets larger than 1272. However, this shouldn't create a problem unless your source application does not resize its packet or it does not receive the ICMP message from the gateway devices.


HTH,


__


Edison.


arunkannan Wed, 01/30/2008 - 09:28
User Badges:

I am not able to ping for more than 1454 bytes.

I dont understand why i am having performance issues when i connect thru layer 3 switch rather than router.

Edison Ortiz Wed, 01/30/2008 - 10:53
User Badges:
  • Super Bronze, 10000 points or more
  • Hall of Fame,

    Founding Member

Are you able to ping with packets greater than 1454 when connecting via the router ?


__


Edison.

arunkannan Thu, 01/31/2008 - 01:48
User Badges:

Can any one tell whether i can do fragmentation on layer 3 switch..is it done default or can i enable it , if yes then how......

david contreras Fri, 06/14/2013 - 09:15
User Badges:

I am having a similar problem.   From my Windows workstation I can not ping the 6500 interface IPs or any devices on those subnets with a ping larger than 993 bytes.  992 bytes pings fine....what the hell would cause this?  I have 2 6509's both running hybrid os, but different os.  Same problem.  Any ideas? One is 12.1(1)E the other is 12.1(19)E1.

From the router/gateway i can ping 1400 bytes no problem to the servers.      

Actions

This Discussion