Sorry for my unclear statement.

I’m using the discovery, STP, l2_multi modules on the controller with the 
diamond topology, like

                                 h1—s0—— s1—— s2—h3
                                         |                       |
                                         |   ——s3——  |
                                                

When I issue a ping on h1 (10.0.0.1) like this
-------------------
root@ubuntu:~# ping 10.0.0.3 -s 1600
PING 10.0.0.3 (10.0.0.3) 1600(1628) bytes of data.
^C
--- 10.0.0.3 ping statistics ---
14 packets transmitted, 0 received, 100% packet loss, time 13102ms
——————————
The ping can never be successful. By default, I can’t see any warning or error 
log information on pox.

If you ping with smaller size packet like 1000 bytes, there isn't any problem. 
After I tested, the threshold is around 1500, I’m thinking it’s because of 
fragmentation.

—————————————————————
root@ubuntu:~# ping 10.0.0.3 -s 1000
PING 10.0.0.3 (10.0.0.3) 1000(1028) bytes of data.
1008 bytes from 10.0.0.3: icmp_req=1 ttl=64 time=268 ms
1008 bytes from 10.0.0.3: icmp_req=2 ttl=64 time=0.061 ms
1008 bytes from 10.0.0.3: icmp_req=3 ttl=64 time=0.052 ms
1008 bytes from 10.0.0.3: icmp_req=4 ttl=64 time=0.057 ms
————————————————
Here is the all log information on the pox side.
———————————— 
pox git:(dart) ./pox.py openflow.discovery openflow.spanning_tree 
forwarding.l2_multi
POX 0.3.0 (dart) / Copyright 2011-2014 James McCauley, et al.
INFO:core:POX 0.3.0 (dart) is up.
INFO:openflow.of_01:[00-00-00-00-00-0c 1] connected
INFO:openflow.of_01:[00-00-00-00-00-0d 4] connected
INFO:openflow.of_01:[00-00-00-00-00-0b 2] connected
INFO:openflow.of_01:[00-00-00-00-00-0a 3] connected
INFO:openflow.discovery:link detected: 00-00-00-00-00-0c.3 -> 
00-00-00-00-00-0d.2
INFO:openflow.discovery:link detected: 00-00-00-00-00-0c.2 -> 
00-00-00-00-00-0b.3
INFO:openflow.discovery:link detected: 00-00-00-00-00-0d.3 -> 
00-00-00-00-00-0a.3
INFO:openflow.discovery:link detected: 00-00-00-00-00-0d.2 -> 
00-00-00-00-00-0c.3
INFO:openflow.spanning_tree:6 ports changed
INFO:openflow.discovery:link detected: 00-00-00-00-00-0b.3 -> 
00-00-00-00-00-0c.2
INFO:openflow.spanning_tree:4 ports changed
INFO:openflow.discovery:link detected: 00-00-00-00-00-0b.2 -> 
00-00-00-00-00-0a.2
INFO:openflow.spanning_tree:1 ports changed
INFO:openflow.discovery:link detected: 00-00-00-00-00-0a.3 -> 
00-00-00-00-00-0d.3
INFO:openflow.spanning_tree:4 ports changed
INFO:openflow.discovery:link detected: 00-00-00-00-00-0a.2 -> 
00-00-00-00-00-0b.2
—————————————————————

Using Ryu as the controller for the same topology
——— ———— ————— 
root@ubuntu:~# ping 10.0.0.3 -s 9999
PING 10.0.0.3 (10.0.0.3) 9999(10027) bytes of data.
10007 bytes from 10.0.0.3: icmp_req=21 ttl=64 time=1.36 ms
10007 bytes from 10.0.0.3: icmp_req=22 ttl=64 time=0.183 ms
10007 bytes from 10.0.0.3: icmp_req=23 ttl=64 time=0.118 ms
10007 bytes from 10.0.0.3: icmp_req=24 ttl=64 time=0.142 ms
10007 bytes from 10.0.0.3: icmp_req=25 ttl=64 time=0.259 ms
10007 bytes from 10.0.0.3: icmp_req=26 ttl=64 time=0.150 ms
10007 bytes from 10.0.0.3: icmp_req=27 ttl=64 time=0.122 ms
10007 bytes from 10.0.0.3: icmp_req=28 ttl=64 time=0.109 ms
10007 bytes from 10.0.0.3: icmp_req=29 ttl=64 time=0.265 ms
————— ————————— 


> On Oct 19, 2014, at 19:42, Murphy McCauley <murphy.mccau...@gmail.com> wrote:
> 
> I don't know what limit you're running into.
> 
> Can you be (much) more specific about what you're trying to do, what you 
> think should be happening, what is happening instead, any relevant errors or 
> log messages, etc.?
> 
> -- Murphy
> 
> On Oct 19, 2014, at 4:35 PM, Tim Huang <pds...@gmail.com> wrote:
> 
>> Hi,
>> 
>> I am modifying the pox code to perform some kind of load balancing on the 
>> controller. However, I found that the maximum ping packet size that pox can 
>> handle is around 1500 bytes which is too small for my test case, then I 
>> tried other controllers like Ryu, Opendaylight, and they don’t have this 
>> kind of limitation.  Is it because of fragmentation or something else? any 
>> clue for this?
> 

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