nixcraft has a tutorial on configuring memcached server(link) at the end says:

For busy memcached server you need to increase system file descriptor and IP port limits

here is the code to do so:

# Increase system IP port limits
net.ipv4.ip_local_port_range = 2000 65000

why should we do this? memcached is a server and it will respond to clients with its listening port which is 11211 by default. So we shouldn't be limited by local port range.(net.ipv4.ip_local_port_range) The only limit is file descriptors. local port range should be a limit for servers like squid which generate local traffic