Tuesday 26 October 2010

Subnet Mask vs Wildcard Mask

Something I find I struggle with is when to use a subnet mask and when to use a wildcard mask. This article is to simply set out the instances when you will use one or the other (not the actual steps to apply them).

Subnet Mask:

  • When applying an IP to an interface
  • Routing protocol summary addresses
  • BGP
  • PIX security appliance ACL's
  • ASA security appliance ACL's
  • When creating DHCP pools on a Switch or Router

Wildcard Mask:
  • EIGRP network statements
  • OSPF network statements
  • VPN concentrator network lists (when setting the local and remote allowed networks)
  • Router ACL's
This list is not exhaustive and I will add to it as I come across new instances where you use either a Subnet mask or Wildcard mask.