Secondary IPv4 addresses can be assigned to an IP interface to allow multiple IP subnets to be assigned to a single Ethernet LAN segment. This is useful in IPv4 address migration and the use of a single VLAN for multiple IP subnets in some network designs.
On the 7210 SAS, IPv4 secondary addresses are supported for the following IP interface types:
IES IP interface
VPRN IP interface
Routed VPLS IP interface
Network IP interface
The following optional functionality is supported with IPv4 secondary addresses:
Use IPv4 secondary addresses with static routes.
Advertise IPv4 secondary addresses through routing protocols such as OSPF or IS-IS.
Use IPv4 secondary addresses with VRRP (IPv4).
The following restrictions apply to the use of IPv4 secondary addresses:
An IP interface must be assigned a primary IP address before a secondary IP address can be used.
Secondary IP addresses cannot be used for setting up OSPF or IS-IS neighbors.
Secondary IP addresses cannot be used with MPLS protocols and PWs (such as RSVP, LDP, or BGP 3107) for specifying parameters such as path information. That is, MPLS protocols and PWs always use primary IPv4 addresses.