All unicast traffic is by default allowed across a router. You can stop this if you apply an access-list. If you haven't added an access-list, it is getting through. If you have you must add the access-list permit rule to allow that traffic.
Check if you have an access-group applied to an interface. If yes do a show access-list to see if it is being blocked by a rule. If blocked, add the permit rule to allow.
Steve