Ended up with the following for DSL customers using DS-Lite:
block size 512
max blocks per user 16
block timeout 120
avg usage is 34 ports per block and 1,3 blocks per address, but the top 1% are at least x10.
Some years ago we had started with more relaxed numbers (to be on the safe side), but last year we squeezed them a little. No complaints until now.
Mon Feb 29 14:25:16.812 CST
!! IOS XR Configuration 5.3.1
service cgn cgn1
service-location preferred-active 0/3/CPU0 service-type nat44 nat1
size Bulk size for allocation.
Should be greater or equal to one fourth of the port limit
and less than twice the port limit.
For optimum results, should be close to half the port limit RP/0/RSP0/CPU0:eng-lab-9k-1(config-cgn-invrf)#bulk-port-alloc size ?
none No bulk allocation
8 Allocate 8 ports in bulk
16 Allocate 16 ports in bulk
32 Allocate 32 ports in bulk
64 Allocate 64 ports in bulk
128 Allocate 128 ports in bulk
256 Allocate 256 ports in bulk
512 Allocate 512 ports in bulk
1024 Allocate 1024 ports in bulk
2048 Allocate 2048 ports in bulk
4096 Allocate 4096 ports in bulk