https://www.thesun.co.uk/news/3370028/russia-putin-north-korea-war-troops-border/
Yes, Russia does have a (small) border with North Korea. Russia controls the Pacific coast to a bit south of Vladivostok, the terminus of the Trans Siberian railway, and home of russia’s Pacific fleet.
The border between the countries is a river, which is crossed by a railroad bridge. Because North Korea uses standard gauge tracks to be compatible with China, the Russian gauge trains cannot be used without a change of gauge.
So far this looks like a defensive deployment to prevent a flood of refugees in the event of an active military confrontation between the US and North Korea.
That is as it should be. The largest impact that few, if any are ready for is the potential for millions of North Korean refugees seeking food and shelter away from the chaos if the NK governmental balloon goes up. Smart money says to man the borders now.