Range of ports for SNMP response?

We are using SNMP for a management tool and are trying to open firewall ports for a couple of servers. Some requests will get through because they are using the default port 161. But, the server that they need to talk to that is running Cacti will send things on random ports. For instance if I do an snmpwalk on the Cacti server and I do a tcpdump on the target server, I get random port numbers from the Cacti server showing up in the tcpdump output. Is there a range that SNMP uses so that I can tell the firewall guys what we need opened?
An example:
15:36:06.395854 IP (tos 0x0, ttl  57, id 0, offset 0, flags [DF], proto: UDP (17), length: 69) 10.178.156.32.38494 > 10.212.24.25.161:  { SNMPv2c { GetNextRequest(26) R=1104629659  .1.3.6.1.2.1.1 } }