Cisco CCNP and CCIE Study Notes

After pinging through a box doing NAT, one might see a NAT entry like the following. The protocol is "icmp" as one expects but there is also a number after the colon in the IP addresses listed in the inside/outside global/local addresses. In the case of UDP or TCP the number after the colon would the port number involved. What does that number signify for the ICMP case?

R3#sh ip nat translations 
Pro Inside global      Inside local       Outside local      Outside global
icmp 172.16.1.5:8      10.1.1.1:8         155.55.55.55:8     155.55.55.55:8

Consider the following configuration on a router doing NAT. It turns out that devices on the inside are unable to ping devices on the outside because the outside devices don't have a route back to the translated source address of 172.16.1.X. Why is that the case when clearly the 172.16.1.0 network is being advertised by OSPF? How can this be fixed?

interface Loopback0
 ip address 172.16.1.1 255.255.255.0
!
interface Ethernet0/0
 ip address 10.1.1.2 255.255.255.0
 ip nat inside
 ip virtual-reassembly
 no keepalive
!
interface Serial2/0
 ip address 171.69.1.1 255.255.255.0
 ip nat outside
 ip virtual-reassembly
 no keepalive
 serial restart-delay 0
!
router eigrp 100
 network 10.0.0.0
 no auto-summary
!
router ospf 10
 log-adjacency-changes
 redistribute static subnets
 network 171.69.1.0 0.0.0.255 area 0
 network 172.16.1.0 0.0.0.255 area 0
!
ip nat pool NATPOOL 172.16.1.2 172.16.1.15 prefix-length 24
ip nat inside source list 1 pool NATPOOL
!
access-list 1 permit 10.0.0.0 0.255.255.255