Changing parameters to counter dst cache overflow

I am using the kernel version 2.6.32 , from a couple of days with traffic running live on the machine I would encounter dst_cache in dmesg logs. It results in system turning to hung state and has to be rebooted eventually.

I want to (tune my kernel)change the parameter values as:

net.ipv4.route.max_size  16777216(Existing Value is 8388608)
net.ipv4.route.gc_thresh  1048576 (Existing Value is 524288)
net.ipv4.route.gc_elasticity to 8 ( It is the same)
rhash_entries(This parameter is missing)

I dont know why is the parameter rhash_entries missing in my sysctl.I need to change four kernel parameter but rhash_entries is missing , could someone help here as to which is the parameter synonymous to rhash_entries . I am using Redhat Linux ....