The alerts are just DNS queries for .pw and .su domains. Often related to torrents webpages, like piratebay.su. You also need to make sure your dns servers, specially 8.8.8.8 is in your HOME_NET of your Snort interface, otherwise if you chose block offenders and select "both" in the which IP to block, your DNS server will get block with those alerts, therefore not allowing any external DNS…. Check if your DNS servers are in the blocked tab of your snort interface.
As for the SNMP, make sure your firewall is configure with some permission to access this service, only allowing your specific IP.
F.