Methods and arrangements for determining indication of maximum datagram size supported without fragmentation in an IP network

1. A method, performed by a first node of an Internet Protocol, IP, network, for determining an indication of a maximum datagram size supported without fragmentation in communication between the first node and a second node of said IP network, wherein the method comprises:

sending, to the second node, request messages in varying sized IP packets using an application layer protocol over User Datagram Protocol, UDP, and which IP packets are configured not to be fragmented by the IP network,

receiving, from the second node, in response to the sent request messages, one or more response messages, respectively, each response message indicating that a datagram of a request message that the response message is in response to, was received by the second node,

identifying a request message of said varying sized IP packets for which there is a change in receipt of response message compared to another request message of said varying sized IP packets, and

determining, based on said identification, an indication of a maximum datagram size supported without fragmentation for application layer data communication over UDP between the first node and the second node.

2. The method as claimed in claim 1 , wherein the indication is a measure that is further determined based on the size of an IP packet of said varying sized that carried a request message resulting in a response message and which IP packet is closest in size to the IP packet of said identified request message.

3. The method as claimed in claim 1 , wherein the varying sized IP packets are being varied in size by being consecutively larger or smaller in size.

4. The method as claimed in claim 1 , wherein the application layer protocol over UDP is Simple Network Management Protocol, SNMP, the first node is operating as a SNMP manager when sending the request messages and the second node is operating as an SNMP agent when sending the response messages.

5. The method as claimed in claim 4 , wherein the request messages are SNMP GetRequest messages and the response messages are SNMP GetResponse messages.

6. The method as claimed in claim 1 , wherein the varying sized IP packets are accomplished by means of varying sized padding in the IP packets.

7. The method as claimed in claim 1 , wherein the response messages are sufficiently small to avoid fragmentation.

8. The method as claimed in claim 1 , wherein the IP network is part of a Radio Access Network, RAN, of a wireless communication network, and/or a Core Network, CN, of the wireless communication network, wherein the first node corresponds to a first radio network node of the RAN and the second node corresponds to a second radio network node of the RAN, or the first node corresponds to a core network node of the CN and the second node corresponds to a radio network node of the RAN, or vice versa.

9. A non-transitory computer readable medium comprising instructions that when executed by a processing circuit causes the first node to perform the method according to claim 1 .

10. A first node for determining an indication of a maximum datagram size supported without fragmentation in communication between the first node and a second node in an Internet Protocol, IP, network, wherein the first node is configured to:

send, to the second node, request messages in varying sized IP packets using an application layer protocol over User Datagram Protocol, UDP, and which IP packets are configured not to be fragmented by the IP network,

receive, from the second node, in response to the sent request messages, one or more response messages, respectively, each response message indicating that a datagram of a request message that the response message is in response to, was received by the second node,

identify a request message of said varying sized IP packets for which there is a change in receipt of response message compared to another request message of said varying sized IP packets, and

determine, based on said identification, an indication of a maximum datagram size supported without fragmentation for application layer data communication over UDP between the first node and the second node.

11. The first node as claimed in claim 10 , wherein the indication is a measure further determined based on the size of an IP packet of said varying sized that carried a request message resulting in a response message and which IP packet is closest in size to the IP packet of said identified request message.

12. The first node as claimed in claim 10 , wherein the varying sized IP packets are being varied in size by being consecutively larger or smaller in size.

13. The first node as claimed in claim 10 , wherein the application layer protocol over UDP is Simple Network Management Protocol, SNMP, the first node is configured to operate as a SNMP manager when sending the request messages and the second node is operating as an SNMP agent when sending the response messages.

14. The first node as claimed in claim 13 , wherein the request messages are SNMP GetRequest messages and the response messages are SNMP GetResponse messages.

15. The first node as claimed in claim 10 , wherein the varying sized IP packets are accomplished by means of varying sized padding in the IP packets.

16. The first node as claimed in claim 10 , wherein the response messages are sufficiently small to avoid fragmentation.

17. The first node as claimed in claim 10 , wherein the IP network is part of a Radio Access Network, RAN, of a wireless communication network, and/or a Core Network, CN, of the wireless communication network, wherein the first node corresponds to a first radio network node configured to be part of the RAN and the second node corresponds to a second radio network node of the RAN, or the first node corresponds to a core network node configured to be part of the CN and the second node corresponds to a radio network node of the RAN, or vice versa.