If you think Texas has a hard time with it's measly 1000 miles of border, you can imagine what it's like to be the biggest country in the world with 14,000 miles of border. It is, needless to say, vastly more complicated to police than anything we can comprehend.
Similar to the US, it brings a number of economic migrants who build their own communities and refuse to assimilate. Many of their migrants are from neighboring Muslim countries. Take this for example that is reminiscent of similar problems in Western Europe with the locals being abused:
https://twitter.com/0xADA1511/status/1771529706363355619
Indeed some parts of Russia are primarily Islamic, such as Chechnya. Indeed there has been a number of attacks over the years:
https://en.m.wikipedia.org/wiki/Category:Islamic_terrorism_in_Russia
Which brings us to our current terrorists, Dalerdzhon Mirzoyev, Shamsidin Fariduni, and Saidakrami Rachabalizoda, Muhammadsobir Fayzov...all from Tajikistan. While I think most agree these were pawns of a higher power, there is much debate on who.
Some might claim Ukraine, or NATO tranny generals.
For myself, and others with permanent ties to Russia, there are concerns for the growing Islamification of ALL Europe (to include Russia). It stands to reason the Islamic world would benefit greatly with Europe and the US destroying each other.
I say this not to condemn nor praise Russia, merely to point out "The West" (and arguably part of the East) face the same problems.