User`s guide

74 XSR User’s Guide
General IP Features Chapter 5
Configuring IP
Unnumbered Interface & Secondary IP
If an unnumbered interface attempts to borrow an IP address from an
Ethernet interface upon which a secondary IP address is configured, only the
primary IP address can be borrowed. Also, sSecondary IP cannot be
configured on an unnumbered interface.
NAT & Secondary IP
Only the primary IP address on the specified interface is used for NAT.
DHCP & Secondary IP
DHCP operates in the same manner regardless if secondary IP addresses are
configured or not. Only one IP pool is employed even if multiple IP addresses
are configured on a single interface.
VPN & Secondary IP
Secondary IP addresses are not supported on VPN virtual interfaces.
Concerning secondary IP addresses assigned to physical interfaces, if an
interface constitutes the endpoint of a VPN tunnel, the primary IP address is
always used as that tunnel endpoint. For the trusted interface upon which
EZ-IPSec Network Extension Mode is running, only the SPD for the primary
IP address assigned to the internal interface will be created.
VRRP & Secondary IP
Multiple virtual IP addresses per Virtual Router (VR) are available to support
multiple logical IP subnets on a single LAN segment. Secondary IP interacts
with the XSR’s implementation of the Virtual Router Redundancy Protocol
(VRRP) as follows:
 The primary physical IP address on an interface will be selected as a
VRRP primary IP address, which is used for VRRP advertisement.
 If one of the virtual IP addresses of a VR is the real physical address
of the interface, all other virtual IP addresses of that VR must also be
the real physical addresses of that interface.
 Conversely, if any virtual IP address is not the real physical address of
that interface, all virtual IP address of that VR cannot be the real
physical address of that interface.