Layer 3 fragmentation

arunkannan · ‎01-30-2008

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.

Edison Ortiz · ‎01-30-2008

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.

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 · ‎01-30-2008

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 · ‎01-30-2008

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

__

Edison.

arunkannan · ‎01-31-2008

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 · ‎06-14-2013

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.