UDP stream network path

[ofri...@annapurnalabs.com]

I have 5 Nodes, and one of them is used as a router, let's say Node #3 is the router.

Nodes 0,1,2 are connected to Node 3 in point-to-point connection.

 

0 -------- 3 -------- 1

              |

 ^           |

 |            |

4 - >      2

And I have another Node, Node #4, that has a network path to Node #0 and Node #2 (some kind of a diamond network).

I'm sending UDP packets with the same src and dst port from Node #4 to Node #1, I see on pcaps that the packet passes throw Node #0, to Node #3,

and gets to Node #1, when #1 replies, the udp ports of the packet are OK, but instead of passing through Node #3 - Node #0 link, the packet transmitted on Node #3 - Node #2 link.

Why doesn't the udp stream follow the same path? Is there a way to make sure it will?

Thanks,

Ofri

[Subhransu Das]

It seems that, there exists a single hop connection between node 4 to node 1,  Please re-check the positioning of the nodes (and calculate the distance between them). Please note that the data will be routed through node 3 iff the paths satisfy routing algorithm criteria. 

May I know which PHY standard is being used here ?

[ofri...@annapurnalabs.com]

I have 3 pcap files for Node #3, one for each interface (without loopback):

1) in the pcap file for interface 1 I see packet from Node #4 to Node #1 (I can tell by IP), this is the interface that used for p2p connection to Node #0.

2) In the second pcap file I see packets from Node #4 to Node #1 and vice versa, this is the interface that is used for p2p connection to Node #1

3) and in the third pcap, that sniffs the interface on the p2p connection between Node #3 and Node #2, I see packets from Node #1 to Node #4. 

=> That means that Node #1 gets the packets, and responses, but on Node #3 (AKA the router), the udp stream is not on the same path.

When I use Tcp it seems to work just fine.

PHY standard? all connections are point-to-point, if that's what you mean.

where udp forward is being done so I can trace on it and maybe get some sights about what is happening?

and both paths have the same numbers of hops.

[Tommaso Pecorella]

Hi,

since the paths in the diamond have identical weight, routing will choose one of them randomly during the routing table construction (well, not really randomly, but almost). Once the RT is built, it is not changed.

This is totally normal and it happens also in the "normal" Internet.

T.