question about icmp permitting on a router

[hellboy101]

Hello all-

Hope all is well with everyone on this forum! The question .. what does this router statement truly mean, for those that know alot more than me

permit icmp any 69.74.53.0 0.0.0.31

Does it mean that pinging is available to this entire global IP range ? what about the subnet range 0.0.0.31? what does this mean?

thx
hb101

 

[ADB100]

It depends on which direction it is applied to an interface. If it is applied inbound (ip access-group xxx in) then it will allow all ICMP traffic coming into the router on the specific interface from any where to subnet 69.74.53.0/27. If it applied outbound (ip access-group xxx out) then it will allow all ICMP traffic passing through (or sourced by) the router from anywhere to subnet 69.74.53.0/27.
The 0.0.0.31 is an inverse mask (the inverse of 255.255.255.224) - when converted to binary a '0' means match and a '1' means ignore. So it must match the first 3 octets (69.74.53) and it must match the first 3 bits of the 4th octet.

0 decimal = 00000000 binary

Match the first 3 bits 000, ignore the last 5 bits so 0 thru 31 will match, any value above 31 won't match.

HTH

Andy