ping fail between 1473- 1476 bytes

[hkobayas]

ping routing-instance  size 1472 172.31.16.2  ---> success

ping routing-instance  size 1473 172.31.16.2  - --> fail

ping routing-instance  size 1474 172.31.16.2 - --> fail

ping routing-instance  size 1475 172.31.16.2  - --> fail

ping routing-instance  size 1476 172.31.16.2  - --> fail

ping routing-instance  size 1477 172.31.16.2  - --> success

When the fragment started because of MTU 1518 on Juniper   MTU 1500 on cisco .

Ping fails. It seems that fragmented packet is not reconstructed again. Between 1473- 1476 bytes

Is this bug ?

[hkobayas]

Are there any recommendation MTU between Cisco 6509 and Juniper Ex 3200

suppose 1518 is not enough. as Vlan tag is 4bytes at leaset we need 1522 on Ex3200

and  over 9221 on cisco side. as there are no option for 1504 bytes.

if we change the MTU. suppose reslove the ping issue.

what everybody think?

[mnarine]

Juniper MTU 1514 bytes is equivalent to Cisco's MTU 1500.  Juniper adds the overhead, Cisco doesn't in the number.  So specifying MTU of 1514 on Juniper is 1500+14 overhead.  Cisco just uses the 1500 and adds the overhead for ethernet.

-Mike

[hkobayas]

Thank you for the info.

one questions

during 1473- 1476 bytes, Packet fragments becasue of MTU. but look like never assembled. as ping fail

after using above 1477 bytes, it starts to be successful  is this know bug?

[mnarine]

I think you should open a JTAC case and find out.  I'm not sure if there are any bugs.

-Mike