SNMP uses community strings to identify sets of variables. A second command reloads the configuration from the same server, along with any changes. You can defend against SNMP with ACLs that limit SNMP access to specific IP source addresses. At the very least, change your community strings, block access to UDP port 161, and use whatever mechanisms your router vendor supports to protect against SNMP abuse. Or, better yet, disable SNMP if you aren't using it.
Some attacks can overwhelm a router.
For instance, if someone within your network launches Mstream, a DoS tool, and floods a target network, it also fills caches used in some router configurations to speed routing decisions. Mstream spoofs source addresses, and since the cache treats each source and destination address pair as a cache entry, it quickly fills with garbage entries.