[AusNOG] Challenge with SQL Replication over multiple carriers

[Darren Moss]

Hello Noggers,

I have a handful of customers with SQL replication issues over 2 separate transit links between Sydney and Melbourne.

Looking to see if anyone here has experienced something similar or could potentially shed some light, perhaps more on my carrier configuration and traffic preferencing.

We have 2x 10GBps interfaces in 2 separate datacentres for transit across 2 carriers. This link carries SQL replication.

It appears when we are using 1 carrier link, everything seems fine and traffic replicates normally.

However, when we balance between 2 carriers, into the same networks, we start seeing issues.

Connections are working, I can telnet, ICMP, etc, however when we start sending large packets we see semaphore timeout errors.

To me it points to TCPOffload, however that's all disabled and I can see no incorrect packets, etc at both sides.

I have even tried routing the SQL traffic over a different network within the same BGP sessions, which works for a while, then eventually starts barfing with semaphore timeout issues.

My question is with traffic preferencing, is there anything special I need to do when using multiple carriers at the same time for the same networks ?

Happy to hear input and suggestions, off list would be better. I am happy to publish what steps were taken.

Many thanks

Darren.
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